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The urgent need to diagnose Sanfilippo syndrome at an early age

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News

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Sat, 10/15/2022 - 00:15

Author(s)

Theodore Bosworth

Sanfilippo syndrome is a rare inherited neurodegenerative metabolic disorder for which there are no approved therapies. Symptoms of the more severe subtypes typically begin within the first years of life, rapidly producing serious and progressive physical and cognitive deficits. The underlying pathophysiology is targetable, but the delay in diagnosis of this as well as other lysosomal storage disorders (LSDs) is slowing progress toward effective therapies.

“Lack of awareness and the delays to diagnosis have been a real challenge for us. There is reason for cautious optimism about treatments now in or approaching clinical studies, but to evaluate efficacy on cognitive outcomes we need to enroll more children at a very young age, before loss of milestones,” according to Cara O’Neill, MD, a co-founder and chief science officer of Cure Sanfilippo Foundation.

Epidemiology and description

Sanfilippo syndrome, like the more than 50 other LSDs, is caused by a gene mutation that leads to an enzyme deficiency in the lysosome.¹ In the case of Sanfilippo syndrome, also known as mucopolysaccharidosis (MPS III), there are hundreds of mutations that can lead to Sanfilippo by altering the function of one of the four genes essential to degradation of heparan sulfate.² Lysosomal accumulation of heparan sulfate drives a broad spectrum of progressive and largely irreversible symptoms that typically begin with somatic manifestations, such as bowel dysfunction and recurrent ear and upper respiratory infections.

Impairment of the central nervous system (CNS) usually occurs early in life, halting physical and mental development. As it progresses, accumulation of heparan sulfate in a variety of cells leads to a cascade of abnormal cellular signaling and dysfunction. Disruption of these processes, which are critical for normal neurodevelopment, result in loss of the developmental skills already gained and eventually loss of brain tissue.³ Although life expectancy has improved with supportive care, survival into adulthood is typically limited to milder forms.⁴

Over the past several years, progress in this and other LSDs has yielded therapeutic targets, including those involving gene repair and enzyme replacement. Already approved for use in some LSDs, these therapies have also shown promise in the experimental setting for Sanfilippo syndrome, leading to several completed clinical trials.⁵

So far, none of these treatments has advanced beyond clinical trials in Sanfilippo syndrome, but there have been favorable changes in the markers of disease, suggesting that better methods of treatment delivery and/or more sensitive tools to measure clinical change might lead to evidence of disease attenuation. However, the promise of treatment in all cases has been to prevent, slow, or halt progression, not to reverse it. This point is important, because it indicates that degree of benefit will depend on enrolling patients early in life. Even if effective therapies are identified, few patients will benefit without strategies to accelerate diagnosis.

In fact, “one study⁶ reported that the average age of diagnosis for Sanfilippo syndrome has not improved over the past 30 years,” according to Dr. O’Neill. She indicated that this has been frustrating, given the availability of clinical trials on which progress is dependent. There is no widely accepted protocol for who and when to test for Sanfilippo syndrome or other LSDs, but Dr. O’Neill’s organization is among those advocating for strategies to detect these diseases earlier, including screening at birth.

Almost by definition, the clinical diagnosis of rare diseases poses a challenge. With nonspecific symptoms and a broad range of potential diagnoses, diseases with a low incidence are not the first ones that are typically considered. In the case of Sanfilippo syndrome, published studies indicate incidence rates at or below 1 per 70,000 live births.⁷ However, the incidence rates have been highly variable not only by geographical regions but even across neighboring countries where genetic risk would be expected to be similar.

In Europe, for example, epidemiologic studies suggest the lifetime risk of MPS IIIA is approximately two times greater in Germany and the Netherlands relative to France and Sweden.⁷ It is possible that the methodology for identifying cases might be a more important factor than differences in genetic risk to explain this variability. Many experts, including Dr. O’Neill, believe that prevalence figures for Sanfilippo syndrome are typically underestimates because of the frequency with which LSDs are attributed to other pathology.

“For these types of rare disorders, a clinician might only see a single case over a career, and the symptoms can vary in presentation and severity with many alternatives to consider in the differential diagnosis,” Dr. O’Neill explained. She cited case reports in which symptoms of Sanfilippo syndrome after a period of initial normal development has been initially attributed to autism, which is a comorbid feature of the disease, idiopathic developmental delay, or other nonprogressive disorders until further clinical deterioration leads to additional testing. The implication is that LSDs must be considered far earlier despite their rarity.

For the least common of the four clinical subtypes, MPS IIIC and MPS IIID, the median ages of diagnosis have ranged from 4.5 to 19 years of age.⁷ This is likely a reflection of a slower progression and a later onset of clinical manifestations.

For the more rapidly progressing and typically more severe subtypes, MPS IIIA and MPS IIIB, the diagnosis is typically made earlier. In one review of epidemiologic studies in different countries, the earliest reported median age at diagnosis was 2.5 years,⁷ a point at which significant disease progression is likely to have already occurred. If the promise of treatments in development is prevention of disease progression, disability in many patients might be substantial if the time to diagnosis is not reduced.

Screening and testing

Independent of the potential to enroll children in clinical trials, early diagnosis also advances the opportunities for supportive care to lessen the burden of the disease on patients and families. Perhaps even more important, early diagnosis is vital to family planning. Since the American pediatrician Sylvester Sanfilippo, MD, first described this syndrome in 1963,⁷ the genetic profile and many of the features of the disease have become well characterized.⁸

“One reason to emphasize the importance of early diagnosis is the heritability of this disorder. With prompt diagnosis, genetic counseling can be offered to families to provide them with critical information for future family planning and for cascade testing of other potentially affected siblings,” Dr. O’Neill reported. The inheritance pattern of Sanfilippo syndrome is autosomal recessive.³ In families with an affected child, the risk for any subsequent child to have the same disorder is 25%. The chance of a sibling to be unaffected and not a carrier is also 25%. There is a 50% chance of a sibling to be a carrier but asymptomatic. Of priorities, spreading awareness has been a critical mission of the Cure Sanfilippo Foundation since it was founded 8 years ago, according to Glenn O’Neill, the president. He and his wife, Dr. O’Neill, who is a pediatrician, founded the organization after their own child’s diagnosis of Sanfilippo syndrome. Creating awareness is fundamental to the mission of attracting funds for research, but support to patients and their families as well as early enrollment in clinical trials are among other initiatives being pursued by the foundation to improve care and prognosis.

These strategies include some novel ideas, including an algorithm based on artificial intelligence (AI) that can accelerate suspicion of Sanfilippo syndrome in advance of laboratory or genetic testing, according to Dr. O’Neill. She reported that the facial phenotype, which is observed in a high proportion of but not in all Sanfilippo patients, includes coarse facial features such as puffiness around the eyes, heavy eyebrows, full lips, and macrocephaly.⁹ Interpretation of photos for AI-based analysis is enhanced when combined with other clinical symptoms.

The facial phenotype, which is observed in a high proportion of but not in all Sanfilippo patients, includes coarse facial features such as puffiness around the eyes, heavy eyebrows, full lips, and macrocephaly.

“The Foundation was involved in honing such a tool by submitting the photos that were used to teach the AI to recognize the Sanfilippo syndrome phenotype,” Dr. O’Neill said. The AI-based tool (Face2Gene.com) is available from FDNA, a company that has been involved in analyzing complex phenotypic and genomic information to guide diagnosis and therapeutic strategies for an array of diseases, not just Sanfilippo syndrome.

The preferred method for diagnosis is biochemical or genetic testing. Of these, urine testing for elevated levels of heparan sulfate glycosaminoglycans (GAG) can be useful for screening, although false-negative tests occur. Analysis of the blood can be performed to detect abnormal levels or activity of the enzymes that break down this GAG. In addition, genetic testing can be performed on blood, fibroblast, buccal swab, or saliva samples. Genetic testing of the blood is the most frequently performed.

For the four MPS III subtypes – MPS IIIA, IIIB, IIIC, and IIID – the presence of two pathogenic mutations in the SGSH (17q25.3), NAGLU (17q21.2), HGSNAT (8p11.21), and GNS (12q14.3) genes, respectively, are likely diagnostic, but enzymatic testing or GAG analysis should be performed to confirm disease status, according to Dr. O’Neill, who said that global consensus based clinical care guidelines led by the Foundation were recently accepted for publication and also include a section on the approach to diagnosis.

While laboratory testing is sensitive, urinary excretion of GAG can be variable, with the potential for ambiguous results. Typically, biochemical and genetic testing provide more reliable results for the diagnosis. They can be readily performed in utero or at the time of birth. In addition, gene panels can permit the diagnosis of multiple types of LSDs, not just Sanfilippo, making screening a cost-effective strategy to consider multiple diseases with overlapping symptoms when an LSD is suspected. Dr. O’Neill said clinical guidelines recommend confirmation of enzyme deficiency or evidence of GAG substrate accumulation as confirmatory tests when genetic testing is positive.

“Ultimately, our goal is to promote universal screening at birth for these serious genetic disorders affecting children,” Dr. O’Neill said.

“We are in a catch-22 when it comes to newborn screening. Currently our federal system requires there be an available treatment before recommending routine screening for a disease. However, it is extremely difficult to power trials with patients who are most likely to show benefit in a trial setting without that very early diagnosis. Universal newborn screening would pave the way for accelerated drug development for children,” she added.

In the meantime, Dr. O’Neill suggests that clinicians should employ a low threshold of suspicion to pursue diagnostic studies of LSDs in infants and children with developmental delays or otherwise unexplained progressive disorders.

Importantly, clinicians can now act quickly on their suspicions and order testing without concern for delays or denial by insurers through a special program, according to Dr. O’Neill. Free genetic testing, offered by the Invitae Corporation, evaluates a panel of 58 genes associated with lysosomal disorders, permitting detection of Sanfilippo syndrome and other LSDs, according to Dr. O’Neill. The Invitae testing is typically performed on 3 mL of whole blood delivered to a central testing facility.

“Results can be obtained within a few weeks or sooner. This can seem like a long wait for families, but it is much more efficient than ordering tests sequentially,” Dr. O’Neill said.

Diagnosis: Signs and symptoms

Despite the differences in progression of the MPS III subtypes, the clinical characteristics are more similar than different. In all patients, prenatal and infant development are typically normal. The initial signs of disease can be found in the newborn, such as neonatal tachypnea, through the early infancy period, such as macrocephaly. However, these are not commonly recognized until about age 1 or soon after in those with MPS IIIA and IIIB.³ Speech delay is the first developmental delay seen in most patients. In those with MPS IIIC, initial symptoms are typically detected at age 3 or later and progress more slowly.^10,11 The same is likely to be true of MPS IIID, although this subtype is less well characterized than the other three.⁷

Although many organs can be involved, degeneration of the CNS is regarded as the most characteristic.³ In aggressive disease, this includes slower acquisition of and failure to meet developmental milestones with progressive intellectual disability, while behavioral difficulties are a more common initial compliant in children with milder disease.¹³^,1⁴ These behavioral changes include hyperactivity, inattention, autistic behaviors, worsening safety awareness, and in some cases aggressive behavior that can be destructive. Sleep disturbances are common.¹⁵Because of variability inherent in descriptions of relatively small numbers of patients, the characterization of each of the MPS III subgroups is based on a limited number of small studies, but most patients demonstrate behavior disorders, have coarse facial features, and develop speech delay, according to a survey conducted of published studies.⁷ Collectively, abnormal behavior was identified as an early symptom in 77% of those with MPS IIIA, 69% of those with IIIB, and 77% of those with IIIC.

For MPS IIIA, loss of speech was observed at a median age of 3.8 years and loss of walking ability at 10.4 years. The median survival has been reported to range between 13 and 18 years. In children with MPS IIIB, the median age of speech loss was reported to about the same age, while loss of walking ability occurred at 11 years. In one study of MPS IIIB, 24% of patients had developed dementia by age 6 years, and the reported median survival has ranged between 17 and 19 years. For MPS IIIC, the onset of clinical symptoms has been observed at a median age of 3.5 years with evidence of cognitive loss observed in 33% of children by the age of 6 years. The median survival has ranged from 19 to 34 years in three studies tracing the natural history of this MPS III subtype.

The differential diagnosis reasonably includes other types of mucopolysaccharidosis disorders with cognitive impairment, including Hurler, Hunter, or Sly syndromes, other neurodevelopmental disorders, and inborn errors of metabolism. The heterogeneity of the features makes definitive laboratory or genetic testing, rather than the effort to differentiate clinical features, appropriate for a definitive diagnosis.

Once the diagnosis is made, other examinations for the common complications of Sanfilippo syndrome are appropriate. Abdominal imaging is appropriate for detecting complications in the gastrointestinal tract, including hepatomegaly, which has been reported in more than half of patients with MPS IIIA and IIIB and in 39% of patients with IIIC.⁷ In patients with breathing concerns at night and/or sleep disturbance, polysomnography can be useful for identifying sleep apnea and nocturnal seizure activity. In children suspected of seizures, EEG is appropriate. In one study, 66% of patients with MPS IIIA developed seizure activity.¹⁶ This has been less commonly reported in MPS IIIB and IIIC, ranging from 8% to 13%.¹⁵

Formal hearing evaluation is indicated for any child with speech delays. Hearing loss typically develops after the newborn period in Sanfilippo and may affect peak language acquisition if not treated, according to Dr. O’Neill.

Radiographic studies for dysostosis multiplex or other skeletal abnormalities are also appropriate based on clinical presentation.

Treatment: Present and future

In the absence of treatments to improve the prognosis of Sanfilippo syndrome, current management is based on supportive care and managing organ-specific complications. However, several strategies have proven viable in experimental models and led to clinical trials. None of these therapies has reached approval yet, but several have been associated with attenuation of biomarkers of MPS III disease activity.

Of nearly 30 Sanfilippo clinical trials conducted over the past 20 years, at least 9 have now been completed.⁵ In addition to studying gene therapy and enzyme replacement therapy, these trials have included stem cell transplantation and substrate reduction therapy, for which the goal is to reduce synthesis of the heparan sulfate GAG to prevent accumulation.⁵ Of this latter approach, promising initial results with genistein, an isoflavone that breaks down heparan sulfate, reached a phase 3 evaluation.¹⁸ Although heparan sulfate levels in the CNS were non-significantly reduced over the course of the trial, the reduction was not sufficient to attenuate cognitive decline.

In other LSDs, several forms of enzyme replacement therapy are now approved. In Fabry disease, for example, recombinant alpha-galactosidase A has now been used for more than 15 years.¹⁹ Clinical benefit has not yet been demonstrated in patients with Sanfilippo syndrome because of the difficulty of delivering these therapies past the blood-brain barrier. Several strategies have been pursued. For example, intrathecal delivery of recombinant heparan-N-sulfatase reduced CNS levels of GAG heparan sulfate in one phase 2B study, but it approached but fell short of the statistical significance for the primary endpoint of predefined cognitive stabilization.²⁰ The signal of activity and generally acceptable tolerability has encouraged further study, including an ongoing study with promising interim results of intracerebroventricular enzyme replacement in MPS IIIB, according to Dr. O’Neill.

Acceptable safety and promising activity on disease biomarkers have also been seen with gene therapy in clinical trials. In one study that showed attenuation of brain atrophy, there was moderate improvement in behavior and sleep in three of the four patients enrolled.²¹ Other studies using various strategies for gene delivery have also produced signals of activity against the underlying pathology, generating persistent interest in ongoing and planned clinical studies with this form of treatment.²²Unmodified hematopoietic stem cell transplantation (HSCT), an approach that has demonstrated efficacy when delivered early in the course of other LSDs, such as Hurler syndrome,²³ has not yet been associated with significant activity in clinical studies of MPS III, including those that initiated treatment prior to the onset of neurological symptoms.²⁴ However, promising early results have been reported in a study of gene-modified HSCT, which overexpresses the MPS IIIA enzyme.

“The clinical trial landscape fluctuates quite a bit, so I always encourage clinicians and families to check back often for updates. Patient organizations can also be helpful for understanding the most up-to-date and emerging trial options,” Dr. O’Neill reported.

Although it is expected that the greatest benefit would be derived from treatments initiated before or very early after the onset of symptoms, based on the limited potential for reversing cognitive loss, Dr. O’Neill said that she and others are also striving to offer treatments for individuals now living with Sanfilippo syndrome.

“We have to be willing to test treatments that are symptomatic in nature. To that aim, the Cure Sanfilippo Foundation has sponsored a study of a CNS-penetrating anti-inflammatory agent in advanced-disease patients more than 4 years of age,” Dr. O’Neill said. This group of patients typically been ineligible for clinical trials in the past. Dr. O’Neill hopes to change this orientation.

“It is important to highlight that all patients deserve our efforts to improve their quality of life and alleviate suffering, regardless of how old they are or how progressed in the disease they happen to be,” she said.

However, whether the goal is enrollment before or early in disease or later in disease progression, the challenge of enrolling sufficient numbers of patients to confirm clinical activity has been and continues to be a hurdle to progress.

“Clinical studies in Sanfilippo enroll relatively small numbers of patients, often 20 or less,” said Dr. O’Neill, explaining one of the reasons why her organization has been so active in raising awareness and funding such studies. For patients and families, the Cure Sanfilippo Foundation can offer a variety of guidance and support, but information about opportunities for clinical trial participation is a key resource they provide for families and their physicians.

Conclusion

For most children with Sanfilippo syndrome, life expectancy is limited. However, the characterization of the genetic causes and the biochemistry of the subtypes has led to several viable therapeutic approaches under development. There has been progress in delivery of therapeutic enzymes to the CNS, and there is substantial optimism that more progress is coming. One issue for treatment development, is the last of a clear regulatory pathway addressing important biomarkers of pathology, such as heparan sulfate burden. Developing treatments that address this issue or impaired enzyme activity levels have promise for preventing progression, particularly if started in infancy. However, the effort to draw awareness to this disease is the first step toward accelerating the time to an early diagnosis and subsequent opportunities to enroll in clinical trials.

References

1. Sun A. Lysosomal storage disease overview. Ann Transl Med. 2018 Dec;6(24):476. doi: 10.21037/atm.2018.11.39.

2. Andrade F et al. Sanfilippo syndrome: Overall review. Pediatr Int. 2015 Jun;57(3):331-8. doi: 10.1111/ped.12636.

3. Fedele AO. Sanfilippo syndrome: Causes, consequences, and treatments. Appl Clin Genet. 2015 Nov 25;8:269-81. doi: 10.2147/TACG.S57672.

4. Lavery C et al. Mortality in patients with Sanfilippo syndrome. Orphanet J Rare Dis. 2017 Oct 23;12(1):168. doi: 10.1186/s13023-017-0717-y.

5. Pearse Y et al. A cure for Sanfilippo syndrome? A summary of current therapeutic approaches and their promise. Med Res Arch. 2020 Feb 1;8(2). doi: 10.18103/mra.v8i2.2045.

6. Kuiper GA et al. Failure to shorten the diagnostic delay in two ultrao-rphan diseases (mucopolysaccharidosis types I and III): potential causes and implication. Orphanet J Rare Dis. 2018;13:2. Doi: 10.1186/s13023-017-0733-y.

7. Zelei T et al. Epidemiology of Sanfilippo syndrome: Results of a systematic literature review. Orphanet J Rare Dis. 2018 Apr 10;13(1):53. doi: 10.1186/s13023-018-0796-4.

8. Wagner VF, Northrup H. Mucopolysaccaharidosis type III. Gene Reviews. 2019 Sep 19. University of Washington, Seattle. https://www.ncbi.nlm.nih.gov/books/NBK546574/8.

9. O’Neill C et al. Natural history of facial features observed in Sanfilippo syndrome (MPS IIIB) using a next generation phenotyping tool. Mol Genet Metab. 2019 Feb;126:S112.

10. Ruijter GJ et al. Clinical and genetic spectrum of Sanfilippo type C (MPS IIIC) disease in the Netherlands. Mol Genet Metab. 2008 Feb;93(2):104-11. doi: 10.1016/j.ymgme.2007.09.011.

11. Valstar MJ et al. Mucopolysaccharidosis type IIID: 12 new patients and 15 novel mutations. Hum Mutat. 2010 May;31(5):E1348-60. doi: 10.1002/humu.21234.

12. Nijmeijer SCM. The attenuated end of phenotypic spectrum in MPS III: from late-onset stable cognitive impairment to non-neuronopathic phenotype. Orphanet J Rare Dis. 2019;14:249. Doi10.1186/s13023-019-1232-0.

13. Nidiffer FD, Kelly TE. Developmental and degenerative patterns associated with cognitive, behavioural and motor difficulties in the Sanfilippo syndrome: An epidemiological study. J Ment Defic Res. 1983 Sep;27 (Pt 3):185-203. doi: 10.1111/j.1365-2788.1983.tb00291.x.

14. Bax MC, Colville GA. Behaviour in mucopolysaccharide disorders. Arch Dis Child. 1995 Jul;73(1):77-81. doi: 10.1136/adc.73.1.77.

15. Fraser J et al. Sleep disturbance in mucopolysaccharidosis type III (Sanfilippo syndrome): A survey of managing clinicians. Clin Genet. 2002 Nov;62(5):418-21. doi: 10.1034/j.1399-0004.2002.620512.x.

16. Valstar MJ et al. Mucopolysaccharidosis type IIIA: Clinical spectrum and genotype-phenotype correlations. Ann Neurol. 2010 Dec;68(6):876-87. doi: 10.1002/ana.22092.

17. Heron B et al. Incidence and natural history of mucopolysaccharidosis type III in France and comparison with United Kingdom and Greece. Am J Med Genet A. 2011 Jan;155A(1):58-68. doi: 10.1002/ajmg.a.33779.

18. Delgadillo V et al. Genistein supplementation in patients affected by Sanfilippo disease. J Inherit Metab Dis. 2011 Oct;34(5):1039-44. doi: 10.1007/s10545-011-9342-4.

19. van der Veen SJ et al. Developments in the treatment of Fabry disease. J Inherit Metab Dis. 2020 Sep;43(5):908-21. doi: 10.1002/jimd.12228.

20. Wijburg FA et al. Intrathecal heparan-N-sulfatase in patients with Sanfilippo syndrome type A: A phase IIb randomized trial. Mol Genet Metab. 2019 Feb;126(2):121-30. doi: 10.1016/j.ymgme.2018.10.006.

21. Tardieu M et al. Intracerebral administration of adeno-associated viral vector serotype rh.10 carrying human SGSH and SUMF1 cDNAs in children with mucopolysaccharidosis type IIIA disease: Results of a phase I/II trial. Hum Gene Ther. 2014 Jun;25(6):506-16. doi: 10.1089/hum.2013.238.

22. Marco S et al. In vivo gene therapy for mucopolysaccharidosis type III (Sanfilippo syndrome): A new treatment horizon. Hum Gene Ther. 2019 Oct;30(10):1211-1121. doi: 10.1089/hum.2019.217.

23. Taylor M et al. Hematopoietic stem cell transplantation for mucopolysaccharidoses: Past, present, and future. Biol Blood Marrow Transplant. 2019 Jul;25(7):e226-e246. doi: 10.1016/j.bbmt.2019.02.012.

24. Sivakumur P, Wraith JE. Bone marrow transplantation in mucopolysaccharidosis type IIIA: A comparison of an early treated patient with his untreated sibling. J Inherit Metab Dis. 1999 Oct;22(7):849-50. doi: 10.1023/a:1005526628598.

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Novel gene-based therapies for neuromuscular diseases

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Author(s)

Nahomi Yewhalashet

Larry J. Davis, PharmD

Neuromuscular diseases (NMDs) are a broad classification of heterogeneous groups of disorders characterized by progressive muscle weakness resulting from muscle or nerve dysfunction.¹ Diagnosis is based on symptoms and a full medical history, as well as on muscle and imaging tests (including electromyography, nerve-conduction studies, magnetic resonance imaging, muscle biopsy, and blood tests) to confirm or rule out specific NMDs.² Early diagnosis of NMDs can be difficult because symptoms overlap with those of many other diseases.

Although individually, NMDs are rare, collectively, they affect approximately 250,000 people in the United States. Disease types vary in regard to cause, symptoms, prevalence, age of onset, progression, and severity. Functional impairment from any NMD can lead to lifelong morbidities and shortened life expectancy.^1,3

Treatment options for NMDs are limited; most target symptoms, not disease progression. Although there is a need for safe and effective gene-based therapies for NMDs, there are challenges to developing and delivering such treatments that have impeded clinical success. These include a lack of understanding about disease pathology and drug targets, limited animal model systems, and few reliable biomarkers that are predictive of therapeutic success.^4,5

Notwithstanding that challenges remain, our understanding of gene expression in NMDs has greatly advanced in the past few decades. This progress has translated into promising results in the gene-therapy field – thereby setting the stage for therapeutic approaches that use novel gene-delivery and gene-manipulation tools.6 These novel approaches include nonviral strategies, such as antisense oligonucleotides (ASOs), and viral-based strategies, such as adeno-associated virus (AAV)-mediated gene silencing and AAV-mediated gene delivery.

In this article, we highlight advancements in the clinical development of gene-based therapies for NMDs. We focus on amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), and Duchenne muscular dystrophy (DMD) because of recent clinical successes in developing such therapies.^1,6,7 We also catalog completed and ongoing clinical trials for ALS, SMA, and DMD (Tables 1-3).

Amyotrophic lateral sclerosis

ALS is caused by progressive degeneration of upper- and lower-motor neurons, which eventually leads to respiratory failure and death 3 to 5 years after disease onset.^7-9 There are two subtypes: Familial ALS (10% of cases) and sporadic ALS (90% of cases). Commonly mutated ALS-associated genes^6,8 are:

Superoxide dismutase type 1 (SOD1).
Chromosome 9 open reading frame 72 (C9orf72).
Transactive response DNA-binding protein 43 (TARDBP).
Fused in sarcoma (FUS).

SOD1-targeted therapy is being studied, with early evidence of clinical success. Mutations in SOD1 account for 10% to 20% of familial ALS cases and 1% to 2% of sporadic ALS cases.^6,10 10 Mutations in C9orf72 account for 25 to 40% of familial ALS cases and 7% of sporadic ALS cases.^8,9,11 Mutations in TARDBP account for 3% of familial ALS cases and 2% of sporadic cases.¹² Mutations in FUS account for 4% of familial ALS cases and 1% of sporadic cases. Overall, these mutant proteins can trigger neurotoxicity, thus inducing motor-neuron death.^6,10

Treatment of ALS

Two treatments for ALS are Food and Drug Administration approved: riluzole (Rilutek), approved in 1995, and edaravone (Radicava), approved in 2017.

Riluzole is an oral anti-excitotoxic glutamate antagonist.¹¹ Approval of riluzole was based on the results of two studies that demonstrated a 2- to 3-month survival benefit.^10,14 For patients who have difficulty swallowing, an oral suspension (Tiglutik, approved in 2018) and an oral film (Exservan, approved in 2019) are available.

Edaravone is a free-radical scavenger that decreases oxidative stress and is administered intravenously (IV).^9,13,14 Findings from clinical trials suggest functional improvement or slower decline in function for some patients.

Although these two agents demonstrate modest therapeutic benefit, neither reverses progression of disease.^10,14

Gene-based therapy for ALS

Many non-viral strategies, including antisense oligonucleotide (ASO), monoclonal antibodies, reverse transcriptase inhibitors, and HGF gene replacement therapy are used as therapeutic approaches to SOD1, C9orf72, and FUS gene mutations in ALS patients, and are being evaluated in clinical studies^14,15 (Table 1^13-17).

Tofersen, also known as BIIB067, is an investigational ASO, administered by intrathecal (IT) injection, that binds to SOD1 mRNA, thus reducing its protein levels.¹⁶ Tofersen was evaluated in the VALOR phase 3 study (ClinicalTrials.gov Identifier: NCT02623699), a three-part randomized, double-blind, placebo-controlled trial: single ascending dose (Part A), multiple ascending dose (B), and fixed dose (C).¹⁰ In Parts A and B, 48 participants received five IT injections of tofersen or placebo over 12 weeks and were followed for an additional 12 weeks. Reduction in SOD1 protein production and neurofilament level in cerebrospinal fluid (CSF) (a potential biomarker of motor-neuron degeneration) was observed, which determined the fixed-dose for Part C.^16,17

Part C examined the efficacy, safety and tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of tofersen, compared with placebo, in adults with ALS who had a confirmed SOD1 mutation.¹⁷ A total of 108 participants were enrolled; 60 were identified as “faster-progressing”; 48, as “slower-progressing.”¹⁸ The primary endpoint of Part C was change from baseline to Week 28 on the Revised ALS Functional Rating Scale (ALSFRS-R) total score. (ALSFRS-R measures overall clinical effect; the score ranges from 0 [no function] to 4 [full function].¹⁷)

Tofersen failed to meet the primary efficacy outcome because statistically significant findings were lacking in the faster-progressing population, as measured by joint-rank analysis (difference of 1.2 on the ALSFRS-R score; P = .97). However, trends favoring tofersen were observed across key secondary clinical outcome measures^18:

Change from baseline in CSF SOD1 protein concentration.¹⁷ Percent reduction in the total SOD1 protein level was much higher in the tofersen-treated group than in the control group (38% more than controls in the faster-progressing population; 26% more than controls in the slower-progressing population).¹⁸
Change from baseline in neurofilament light-chain concentration in plasma.^17,18 Percent reduction in the level of neurofilament light chain was also observed to be higher in the tofersen-treated group than in the control group (67% more than controls in the faster-progressing population and 48% more than controls in the slower-progressing population).¹⁸

Because of these encouraging results, VALOR participants were moved to the ongoing open-label extension trial of tofersen (ClinicalTri-als.gov Identifier: NCT03070119), in which both groups were treated with the active agent.

These data suggest that early tofersen treatment might slow decline in faster-progressing patients and stabilize clinical function in slower-progressing patients.^18,19 Overall, most adverse events (AEs) in the trial among patients receiving active treatment were of mild or moderate severity, and were largely consistent with either disease progression or lumbar puncture–related complications.¹⁸

Because data from VALOR suggested potential benefit from tofersen, the ATLAS trial (ClinicalTrials.gov Identifier: NCT04856982) is investigating the clinical value of presymptomatic treatment and the optimal timing of initiation of therapy.^20,21 ATLAS is a phase 3, randomized, placebo-controlled trial that examines the clinical efficacy, safety, and tolerability of tofersen in presymptomatic adult carriers of SOD1 mutation who have an elevated neurofilament light-chain concentration.²¹ ATLAS will also evaluate the efficacy of tofersen when initiated before, rather than after, ALS manifests clinically. Enrollment is still open for this trial.^20,21

Latozinemab, also known as AL001, is a first-in-class monoclonal antibody, administered by IV infusion, that elevates levels of progranulin, a key regulator of the immune activity and lysosomal function in the brain.^22,23 Latozinemab limits progranulin endocytosis and degradation by sortilin inhibition.²² Progranulin gene mutations can reduce progranulin expression (by 50 to 70 percent reduction), which may cause neuro-degeneration due to abnormal accumulation of TAR-DNA-binding protein 43 (TDP-43) in the brain cells.^22,24 TDP-43 pathology has also been shown to be associated with C9orf72 mutations.²³ Although the mechanism is not fully understood, the role of progranulin deficiency in TDP-43 pathology is believed to be associated with neurodegenerative diseases like ALS.11,23,24,43 Previous animal models of chronic neurodegenera-tion have demonstrated how increased progranulin levels can be protective against TDP-43 pathology, increasing neuronal development and survival, thus potentially slowing disease progression.^23,24,43 Currently, latozinemab is being investigated in a randomized, double-blind, placebo-controlled, multicenter phase 2 trial (ClinicalTrials.gov Identifier: NCT05053035). Approximately, 45 C90rf72-associated ALS participants (≥ 18 years of age) will receive latozinemab or placebo infusions every 4 weeks (for 24 weeks). Study endpoints include safety, tolerability, PK, PD, as well as plasma, and CSF progranulin levels.²⁵ In previous studies, latozinemab demonstrated encouraging results in frontotemporal dementia (FTD) patients who carry a progranulin mutation. Because FTD was revealed to have significant genetic overlap with ALS, there is disease-modifying potential for latozinemab in ALS patients.^23,24

TPN-101 is a nucleoside analog reverse transcriptase inhibitor, administered orally, that was originally developed for human immunodeficiency virus (HIV) treatment. However, due to recent findings suggesting retrotransposon activity contributing to neurodegeneration in TDP-43 mediated diseases, including ALS and FTD, TNP-101 is being repurposed.²⁶ The safety and tolerability of TNP-101 are currently being evaluated in C9orf72-associated ALS and FTD patients (≥ 18 years of age). The study is a randomized, double-blind, placebo-controlled paral-lel-group phase 2a trial (ClinicalTrials.gov Identifier: NCT04993755) The study includes a screening period of 6 weeks, double-blind treatment period of 24 weeks, an open-label treatment period of 24 weeks, and 4 weeks of the post-treatment follow-up visit. Study endpoints include the incidence and severity of spontaneously reported treatment-emergent adverse events (TEAEs) associated with TNP-101 and placebo for a to-tal of 48 weeks.²⁷

ION363 is an investigational ASO, administered by IT injection, that selectively targets one of the FUS mutations (p.P525L), which is responsible for earlier disease onset and rapid ALS progression.^28,29 The clinical efficacy of ION363, specifically in clinical function and survival is being assessed in FUS-associated ALS patients (≥ 12 years of age). This randomized phase 3 study (ClinicalTrials.gov Identifier: NCT04768972) includes two parts; part 1 will consist of participants receiving a multi-dose regimen (1 dose every 4-12 weeks) of ION363 or placebo for 61 weeks followed by an open-label extension treatment period in part 2, which will consist of participants receiving ION363 (every 12 weeks) for 85 weeks. The primary endpoint of the study is the change from baseline to day 505 in functional impairment, using ALS Functional Rating Scale-Revised (ALSFRS-R). This measures functional disease severity, specifically in bulbar function, gross motor skills, fine motor skills, and respiratory. The score for all 12 questions can range from 0 (no function) to 4 (full function) with a total possible score of 48.³⁰

Engensis, also known as VM202, is a non-viral gene therapy, administered by intramuscular (IM) injection, that uses a plasmid to deliver the hepatocyte growth factor (HGF) gene to promote HGF protein production. The HGF protein plays a role in angiogenesis, the previous of muscle atrophy, and the promotion of neuronal survival and growth. Based on preclinical studies, increasing HGF protein production has been shown to reduce neurodegeneration, thus potentially halting or slowing ALS progression.³¹ Currently, the safety of engensis is being evaluated in ALS patients (18-80 years of age) in the REViVALS phase 2a (ClinicalTrials.gov Identifier: NCT04632225)/2b (ClinicalTrial.gov Identifier: NCT05176093).^32,33 The ReViVALS trial is a double-blind, randomized, placebo-controlled, multi-center study. The phase 2a study endpoints include the incidence of TEAEs, treatment-emergent serious adverse events (TESAEs), injection site reactions, and clinically significant labor-atory values post-treatment (engensis vs placebo group) for 180 days.³³ A phase 2b study will evaluate the long-term safety of engensis for an additional 6 months. Study endpoints include the incidence of AEs, changes from baseline in ALSFRS-R scores to evaluate improvement in muscle function, changes from baseline in quality of life using the ALS patient assessment questionnaire, time to all-cause mortality compared to placebo, etc.³²

Spinal muscular atrophy

SMA is a hereditary lower motor-neuron disease caused (in 95% of cases) by deletions or, less commonly, by mutations of the survival motor neuron 1 (SMN1) gene on chromosome 5q13 that encodes the SMN protein.⁶ Reduction in expression of the SMN protein causes motor neurons to degenerate.^36-38 Because of a large inverted duplication in chromosome 5q, two variants of SMN (SMN1 and SMN2) exist on each allele. The paralog gene, SMN2, also produces the SMN protein – although at a lower level (10% to 20% of total SMN protein production) than SMN1 does.

A single nucleotide substitution in SMN2 alters splicing and suppresses transcription of exon 7, resulting in a shortened mRNA strand that yields a truncated SMN protein product.^6,37,39 SMA is classified based on age of onset and maximum motor abilities achieved, ranging from the most severe (Type 0) to mildest (Type 4) disease.^36,40 Because SMA patients lack functional SMN1 (due to polymorphisms), disease severity is determined by copy numbers of SMN2.^6,39

Gene-based therapy for SMA

Three FDA-approved SMN treatments demonstrate clinically meaningful benefit in SMA: SMN2-targeting nusinersen [Spinraza] and risdiplam [Evrysdi], and SMN1-targeting onasemnogene abeparvovec-xioi [Zolgensma]³⁸ Additional approaches to SMA treatment are through SMN-independent therapies, which target muscle and nerve function. Research has strongly suggested that combined SMA therapies, specifically approved SMN-targeted and investigational SMN-independent treatments, such as GYM329 (also known as RO7204239) may be the best strategy to treat all ages, stages, and types of SMA.⁴¹ (Table 2^26-41).

Agents that modulate SMN2. Nusinersen, approved by the FDA in 2016, was the first treatment indicated for all SMA types in pediatric and adult patients.⁴² The agent is an ASO that targets exon 7 of SMN2, thus stabilizing transcription. Inclusion of exon 7 increases SMN protein production, improving motor function.^6,38 Nusinersen is a lifelong treatment that requires IT administration every 4 months because it cannot cross the blood-brain barrier.^38,43

Pivotal clinical studies that led to approval of nusinersen include CHERISH (ClinicalTrial.gov Identifier: NCT02292537) and ENDEAR (ClinicalTrial.gov Identifier: NCT02193074) studies.

CHERISH was a phase 3, randomized, double-blind, sham procedure–controlled trial that examined the clinical efficacy and safety of nusinersen in 126 participants with later-onset SMA (2-12 years of age). The primary endpoint was the change from baseline using the Hammersmith Functional Motor Scale Expanded (HFMSE) at 15 months. HFMSE looks at 33 activities to assess improvement in motor function. The study met the primary efficacy outcome, demonstrating statistically significant (P = .0000001) improvement in overall motor function. The nusinersen group showed a 3.9-point increase in the HFMSE score from baseline, which indicates improvement, compared with a 1.0-point decline from baseline in the control group.^46,47

ENDEAR was also a randomized, double-blind, sham procedure–controlled phase 3 trial, which investigated the efficacy and safety of nusinersen in 121 participants with early-onset SMA Type 1 (≤ 210 days of age). Coprimary endpoints were:

Percentage of motor milestones responders, as determined using Section 2 of the Hammersmith Infant Neurological Examination–Part 2.
Event-free survival (that is, avoidance of combined endpoint of death or permanent ventilation).

ENDEAR met the first primary efficacy outcome, demonstrating statistically significant (P < .0001) improvement in motor milestones (head control, rolling, independent sitting, and standing). By 13 months of age, approximately 51% of nusinersen-treated participants showed improvement, compared with none in the control group.^46,47

The second primary endpoint was also met, with a statistically significant (P = .005) 47% decrease in mortality or permanent ventilation use.^46-48

The NURTURE (ClinicalTrial.gov Identifier: NCT02386553) study is also investigating the efficacy and safety of nusinersen. An ongoing, open-label, supportive phase 2 trial, NURTURE is evaluating the efficacy and safety of multiple doses of nusinersen in 25 presymptomatic SMA patients (≤ 6 weeks of age). The primary endpoint of this study is time to death or respiratory intervention.⁴⁹ Interim results demonstrate that 100% of presymptomatic infants are functioning without respiratory intervention after median follow-up of 2.9 years.^46-48

Although nusinersen has been shown to be generally safe in clinical studies, development of lumbar puncture–related complications, as well as the need for sedation during IT administration, might affect treatment tolerability in some patients.³⁹

Risdiplam was approved by the FDA in 2020 as the first orally administered small-molecule treatment of SMA (for patients ≤ 2 months of age).⁵² Risdiplam is a SMN2 splicing modifier, binding to the 5’ splice site of intron 7 and exonic splicing enhancer 2 in exon 7 of SMN2 pre-mRNA. This alternative splicing increases efficiency in SMN2 gene transcription, thus increasing SMN protein production in motor-neuron cells.³⁶ An important advantage of risdiplam is the convenience of oral administration: A large percentage of SMA patients (that is, those with Type 2 disease) have severe scoliosis, which can further complicate therapy or deter patients from using a treatment that is administered through the IT route.⁴⁰

FDA approval of risdiplam was based on clinical data from two pivotal studies, FIREFISH (ClinicalTrial.gov Identifier: NCT02913482) and SUNFISH (ClinicalTrial.gov Identifier: NCT02908685).^53-54

FIREFISH is an open-label, phase 2/3 ongoing trial in infants (1-7 months of age) with SMA Type 1. The study comprises two parts; Part 1 determined the dose of risdiplam used in Part 2, which assessed the efficacy and safety of risdiplam for 24 months. The primary endpoint was the percentage of infants sitting without support for 5 seconds after 12 months of treatment using the gross motor scale of the Bayley Scales of Infant and Toddler Development–Third Edition. A statistically significant (P < .0001) therapeutic benefit was observed in motor milestones. Approximately 29% of infants achieved the motor milestone of independent sitting for 5 seconds, which had not been observed in the natural history of SMA.^53-55

SUNFISH is an ongoing randomized, double-blind, placebo-controlled trial of risdiplam in adult and pediatric patients with SMA Types 2 and 3 (2-25 years old). This phase 2/3 study comprises two parts: Part 1 determined the dose (for 12 weeks) to be used for confirmatory Part 2 (for 12 to 24 months). The primary endpoint was the change from baseline on the 32-item Motor Function Measure at 12 months. The study met its primary endpoint, demonstrating statistically significant (P = .0156) improvement in motor function scores, with a 1.36-point increase in the risdiplam group, compared with a 0.19-point decrease in the control group.^54,55

Ongoing risdiplam clinical trials also include JEWELFISH (ClinicalTrial.gov Identifier: NCT03032172) and RAINBOW (ClinicalTrial.gov Identifier: NCT03779334).^56-57 JEWELFISH is an open-label, phase 2 trial assessing the safety of risdiplam in patients (6 months to 60 years old) who received prior treatment. The study has completed recruitment; results are pending.⁵⁶ RAINBOW is an ongoing, open-label, single-arm, phase 2 trial, evaluating the clinical efficacy and safety of risdiplam in SMA-presymptomatic newborns (≤ 6 weeks old). The study is open for enrollment.⁵⁷ Overall, interim results for JEWELFISH and RAINBOW appear promising.

In addition, combined SMA therapies, specifically risdiplam and GYM329 are currently being investigated to address the underlying cause and symptoms of SMA concurrently.⁵⁸ GYM329, is an investigational anti-myostatin antibody, selectively binding preforms of myostatin - pro-myostatin and latent myostatin, thus improving muscle mass and strength for SMA patients.⁵⁹ The safety and efficacy of GYM329 in combination with risdiplam is currently being investigated in 180 ambulant participants with SMA (2-10 years of age) in the MANATEE (ClinicalTrial.gov Identifier: NCT05115110) phase 2/3 trial. The MANATEE study is a two-part, seamless, randomized, placebo-controlled, double-blind trial. Part 1 will assess the safety of the combination treatment in approximately 36 participants; participants will receive both GYM329 (every 4 weeks) by subcutaneous (SC) injection into the abdomen and risdiplam (once per day) for 24 weeks followed by a 72-week open-label treatment period. ^54,58 The outcome measures include the incidence of AEs, percentage change from baseline in the contractile area of skeletal muscle (in dominant thigh and calf), change from baseline in RHS total score, and incidence of change from baseline in serum concentration (total myostatin, free latent myostatin, and mature myostatin) etc.⁵⁴ Part 2 will be conducted on 144 participants, specifically assessing the efficacy and safety of the optimal dose of GYM329 selected from Part 1 (combined with risdiplam) for 72 weeks. Once the treatment period is completed in either part, participants can partake in a 2-year open-label extension period.^54,58 Other outcome measures include change from baseline in lean muscle mass (assessed by full body dual-energy X- ray absorptiometry (DXA) scan), in time taken to walk/run 10 meters (measured by RHS), in time taken to rise from the floor (measured by RHS), etc.⁵⁴ Overall, this combination treatment has the potential to further improve SMA patient outcomes and will be further investigated in other patient populations (including non-ambulant patients and a broader age range) in the future.⁵⁸

An agent that alters SMN1 expression. Onasemnogene abeparvovec-xioi, FDA approved in 2019, was the first gene-replacement therapy indicated for treating SMA in children ≤ 2 years old.⁶⁰ Treatment utilizes an AAV vector type 9 (AAV9) to deliver a functional copy of SMN1 into target motor-neuron cells, thus increasing SMN protein production and improving motor function. This AAV serotype is ideal because it crosses the blood-brain barrier. Treatment is administered as a one-time IV fusion.^38,39,43

FDA approval was based on the STR1VE (ClinicalTrial.gov Identifier: NCT03306277) phase 3 study and START (ClinicalTrial.gov Identifier: NCT02122952) phase 1 study.^61,62 START was the first trial to investigate the safety and efficacy of onasemnogene abeparvovec-xioi in SMA Type 1 infants (< 6 months old). Results demonstrated remarkable clinical benefit, including 100% permanent ventilation-free survival and a 92% (11 of 12 patients) rate of improvement in motor function. Improvement in development milestones was also observed: 92% (11 of 12 patients) could sit without support for 5 seconds and 75% (9 of 12) could sit without support for 30 seconds.^14,61,63

The efficacy of onasemnogene abeparvovec-xioi seen in STR1VE was consistent with what was observed in START. STRIVE, a phase 3 open-label, single-dose trial, examined treatment efficacy and safety in 22 symptomatic infants (< 6 months old) with SMA Type 1 (one or two SMN2 copies). The primary endpoint was 30 seconds of independent sitting and event-free survival. Patients were followed for as long as 18 months. Treatment showed statistically significant (P < .0001) improvement in motor milestone development and event-free survival, which had not been observed in SMA Type 1 historically. Approximately 59% (13 of 22 patients) could sit independently for 30 seconds at 18 months of age. At 14 months of age, 91% (20 of 22 patients) were alive and achieved independence from ventilatory support.^34,35,53

Although many clinical studies suggest that onasemnogene abeparvovec-xioi can slow disease progression, the benefits and risks of long-term effects are still unknown. A 15-year observational study is investigating the long-term therapeutic effects and potential complications of onasemnogene abeparvovec-xioi. Participants in START were invited to enroll in this long-term follow-up study (ClinicalTrial.gov Identifier: NCT04042025).^66-67

Duchenne muscular dystrophy

DMD is the most common muscular dystrophy of childhood. With an X-linked pattern of inheritance, DMD is seen mostly in young males (1 in every 3,500 male births).^38,39,73 DMD is caused by mutation of the dystrophin encoding gene, or DMD, on the X chromosome. Deletion of one or more exons of DMD prevents production of the dystrophin protein, which leads to muscle degeneration.^38,39,43 Common DMD deletion hotspots are exon 51 (20% of cases), exon 53 (13% of cases), exon 44 (11% of cases), and exon 45 (12% of cases).⁷⁴ Nonsense mutations, which account for another 10% of DMD cases, occur when premature termination codons are found in the DMD gene. Those mutations yield truncated dystrophin protein products.^39,66

Therapy for DMD

There are many therapeutic options for DMD, including deflazacort (Emflaza), FDA approved in 2017, which has been shown to reduce inflammation and immune system activity in DMD patients (≥ 5 years old). Deflazacort is a corticosteroid prodrug; its active metabolite acts on the glucocorticoid receptor to exert anti-inflammatory and immunosuppressive effects. Studies have shown that muscle strength scores over 6-12 months and average time to loss of ambulation numerically favored deflazacort over placebo.^74,75

Gene-based therapy for DMD

Mutation-specific therapeutic approaches, such as exon skipping and nonsense suppression, have shown promise for the treatment of DMD (Table 3^58-79):

ASO-mediated exon skipping allows one or more exons to be omitted from the mutated DMD mRNA.^74,75 Effective FDA-approved ASOs include golodirsen [Vyondys 53], viltolarsen [Viltepso], and casimersen [Amondys 45].⁷⁴
An example of therapeutic suppression of nonsense mutations is ataluren [Translarna], an investigational agent that can promote premature termination codon read-through in DMD patients.⁶⁶

Another potential treatment approach is through the use of AAV gene transfer to treat DMD. However, because DMD is too large for the AAV vector (packaging size, 5.0 kb), microdystrophin genes (3.5-4 kb, are used as an alternative to fit into a single AAV vector.^39,76

Exon skipping targeting exon 51. Eteplirsen, approved in 2016, is indicated for the treatment of DMD patients with the confirmed DMD gene mutation that is amenable to exon 51 skipping. Eteplirsen binds to exon 51 of dystrophin pre-mRNA, causing it to be skipped, thus, restoring the reading frame in patients with DMD gene mutation amenable to exon 51 skipping. This exclusion promotes dystrophin production. Though the dystrophin protein is still functional, it is shortened.^38,77 Treatment is administered IV, once a week (over 35-60 minutes). Eteplirsen’s accelerated approval was based on 3 clinical studies (ClinicalTrial.gov Identifier: NCT01396239, NCT01540409, and NCT00844597.) ^78-81 The data demonstrated an increased expression of dystrophin in skeletal muscles in some DMD patients treated with eteplirsen. Though the clinical benefit of eteplirsen (including improved motor function) was not established, it was concluded by the FDA that the data were reasonably likely to predict clinical benefit. Continued approval for this indication may depend on the verification of a clinical benefit in confirmatory trials. Ongoing clinical trials include (ClinicalTrial.gov Identifier: NCT03992430 (MIS51ON), NCT03218995, and NCT03218995).^77,81,82

Vesleteplirsen, is an investigational agent that is designed for DMD patients who are amendable to exon 51 skip-ping. The mechanism of action of vesleteplirsen appears to be similar to that of eteplirsen.⁸³ The ongoing MOMENTUM (ClinicalTrial.gov Identifier: NCT04004065) phase 2 trial is assessing the safety and tolerability of vesleteplirsen at multiple-ascending dose levels (administered via IV infusion) in 60 participants (7-21 years of age). The study consists of two parts; participants receive escalating dose levels of vesleteplirsen (every 4 weeks) for 72 weeks during part A and participants receive the selected doses from part A (every 4 weeks) for 2 years during part B. Study endpoints include the number of AEs (up to 75 weeks) and the change from baseline to week 28 in dystrophin protein level. 84 Serious AEs of reversible hypomagnesemia were observed in part B, and as a result, the study protocol was amended to include magnesium supplementation and monitoring of magnesium levels.⁸³

Exon skipping targeting exon 53. Golodirsen, FDA approved in 2019, is indicated for the treatment of DMD in patients who have a confirmed DMD mutation that is amenable to exon 53 skipping. The mechanism of action is similar to eteplirsen, however, golodirsen is designed to bind to exon 53.^38,39 Treatment is administered by IV infusion over 35-60 minutes.

Approval of golodirsen was based primarily on a two-part, phase 1/2 clinical trial (ClinicalTrial.gov Identifier: NCT02310906). Part 1 was a randomized, placebo-controlled, dose-titration study that assessed multiple-dose efficacy in 12 DMD male patients, 6 to 15 years old, with deletions that were amenable to exon 53 skipping.

Part 2 was an open-label trial in 12 DMD patients from Part 1 of the trial plus 13 newly enrolled male DMD patients who were also amenable to exon 53 skipping and who had not already received treatment. Primary endpoints were change from baseline in total distance walked during the 6-minute walk test at Week 144 and dystrophin protein levels (measured by western blot testing) at Week 48. A statistically significant increase in the mean dystrophin level was observed, from a baseline 0.10% mean dystrophin level to a 1.02% mean dystrophin level after 48 weeks of treatment (P < .001). Common reported adverse events associated with golodirsen were headache, fever, abdominal pain, rash, and dermatitis. Renal toxicity was observed in preclinical studies of golodirsen but not in clinical studies.^80,85

Viltolarsen, approved in 2020, is also indicated for the treatment of DMD in patients with deletions amenable to exon 53 skipping. The mechanism of action and administration (IV infusion over 60 minutes) are similar to that of golodirsen.

Approval of viltolarsen was based on two phase 2 clinical trials (ClinicalTrial.gov Identifier: NCT02740972 and NCT03167255) in a total of 32 patients. NCT02740972 was a randomized, double-blind, placebo-controlled, dose-finding study that evaluated the clinical efficacy of viltolarsen in 16 male DMD patients (4-9 years old) for 24 weeks.

NCT03167255 was an open-label study that evaluated the safety and tolerability of viltolarsen in DMD male patients (5-18 years old) for 192 weeks. The efficacy endpoint was the change in dystrophin production from baseline after 24 weeks of treatment. A statistically significant increase in the mean dystrophin level was observed, from a 0.6% mean dystrophin level at baseline to a 5.9% mean dystrophin level at Week 25 (P = .01). The most common adverse events observed were upper respiratory tract infection, cough, fever, and injection-site reaction.^86-87

Exon skipping targeting exon 45. Casimersen was approved in 2021 for the treatment of DMD in patients with deletions amenable to exon 45 skipping.⁸⁸ Treatment is administered by IV infusion over 30-60 minutes. Approval was based on an increase in dystrophin production in skeletal muscle in treated patients. Clinical benefit was reported in interim results from the ESSENCE (ClinicalTrial.gov Identifier: NCT02500381) study, an ongoing double-blind, placebo-controlled phase 3 trial that is evaluating the efficacy of casimersen, compared with placebo, in male participants (6-13 years old) for 48 weeks. Efficacy is based on the change from baseline dystrophin intensity level, determined by immunohistochemistry, at Week 48.

Interim results from ESSENCE show a statistically significant increase in dystrophin production in the casimersen group, from a 0.9% mean dystrophin level at baseline to a 1.7% mean dystrophin level at Week 48 (P = .004); in the control group, a 0.54% mean dystrophin level at baseline increased to a 0.76% mean dystrophin level at Week 48 (P = .09). Common adverse events have included respiratory tract infection, headache, arthralgia, fever, and oropharyngeal pain. Renal toxicity was observed in preclinical data but not in clinical studies.^60,84

Targeting nonsense mutations. Ataluren is an investigational, orally administered nonsense mutation suppression therapy (through the read-through of stop codons).³⁷ Early clinical evidence supporting the use of ataluren in DMD was seen in an open-label, dose-ranging, phase 2a study (ClinicalTrial.gov Identifier: NCT00264888) in male DMD patients (≥ 5 years old) caused by nonsense mutation. The study demonstrated a modest (61% ) increase in dystrophin expression in 23 of 38 patients after 28 days of treatment.^37,91,92

However, a phase 2b randomized, double-blind, placebo-controlled trial (ClinicalTrial.gov Identifier: NCT00592553) and a subsequent confirmatory ACT DMD phase 3 study (ClinicalTrial.gov Identifier: NCT01826487) did not meet their primary endpoint of improvement in ambulation after 48 weeks as measured by the 6-minute walk test.^37,93,94 In ACT DMD, approximately 74% of the ataluren group did not experience disease progression, compared with 56% of the control group (P = 0386), measured by a change in the 6-minute walk test, which assessed ambulatory decline.^37,95

Based on limited data showing that ataluren is effective and well tolerated, the European Medicines Agency has given conditional approval for clinical use of the drug in Europe. However, ataluren was rejected by the FDA as a candidate therapy for DMD in the United States.²² Late-stage clinical studies of ataluren are ongoing in the United States.

AAV gene transfer with microdystrophin. Limitations on traditional gene-replacement therapy prompted exploration of gene-editing strategies for treating DMD, including using AAV-based vectors to transfer microdystrophin, an engineered version of DMD, into target muscles.⁴³ The microdystrophin gene is designed to produce a functional, truncated form of dystrophin, thus improving muscular function.

There are 3 ongoing investigational microdystrophin gene therapies that are in clinical development (ClinicalTrial.gov Identifier: NCT03368742 (IGNITE DMD), NCT04281485 (CIFFREO), and NCT05096221 (EMBARK)).^38,82

IGNITE DMD is a phase 1/2 randomized, controlled, single-ascending dose trial evaluating the safety and efficacy of a SGT-001, single IV infusion of AAV9 vector containing a microdystrophin construct in DMD patients (4-17 years old) for 12 months. At the conclusion of the trial, treatment and control groups will be followed for 5 years. The primary efficacy endpoint is the change from baseline in microdystrophin protein production in muscle-biopsy material, using western blot testing.⁹⁶ Long-term interim data on biopsy findings from three patients demonstrated clinical evidence of durable microdystrophin protein expression after 2 years of treatment.^96,97

The CIFFREO trial will assess the safety and efficacy of the PF-06939926 microdystrophin gene therapy, an investigational AAV9 containing microdystrophin, in approximately 99 ambulatory DMD patients (4-7 years of age). The study is a randomized, double-blind, placebo-controlled, multicenter phase 3 trial. The primary efficacy end-point is the change from baseline in the North Star Ambulatory Assessment (NSAA), which measures gross motor function. This will be assessed at 52 weeks; all study participants will be followed for a total of 5 years post-treatment.^98,99,100 Due to unexpected patient death (in a non-ambulatory cohort) in the phase 1b (in a non-ambulatory cohort) in the phase 1b (ClinicalTrial.gov Identifier: (NCT03362502) trial, microdystrophin gene therapy was immediately placed on clinical hold.^101,102 The amended study protocol required that all participants undergo one week of in-hospital observation after receiving treatment.¹⁰²

The EMBARK study is a global, randomized, double-blind, placebo-controlled, phase 3 trial that is evaluating the safety and efficacy of SRP-9001, which is a rAAVrh74.MHCK7.microdystrophin gene therapy. The AAV vector (rAAVrh74) contains the microdystrophin construct, driven by the skeletal and cardiac muscle–specific promoter, MHCK7.98,99 In the EMBARK study, approximately 120 participants with DMD (4-7 years of age) will be enrolled. The primary efficacy endpoint includes the change from baseline to week 52 in the NSAA total score.⁹⁹ Based on SRP-9001, data demonstrating consistent statistically significant functional improvements in NSAA total scores and timed function tests (after one-year post- treatment) in DMD patients from previous studies and an integrated analysis from multiple studies (ClinicalTrial.gov Identifier: NCT03375164, NCT03769116, and NCT04626674), the ongoing EMBARK has great promise.^103,104

Challenges ahead, but advancements realized

Novel gene-based therapies show significant potential for transforming the treatment of NMDs. The complex pathologies of NMDs have been a huge challenge to disease management in an area once considered unremediable by gene-based therapy. However, advancements in precision medicine – specifically, gene-delivery systems (for example, AAV9 and AAVrh74 vectors) combined with gene modification strategies (ASOs and AAV-mediated silencing) – have the potential to, first, revolutionize standards of care for sporadic and inherited NMDs and, second, significantly reduce disease burden.⁶

What will be determined to be the “best” therapeutic approach will, likely, vary from NMD to NMD; further investigation is required to determine which agents offer optimal clinical efficacy and safety profiles.⁴³ Furthermore, the key to therapeutic success will continue to be early detection and diagnosis – first, by better understanding disease pathology and drug targets and, second, by validation of reliable biomarkers that are predictive of therapeutic benefit.^4,5

To sum up, development challenges remain, but therapeutic approaches to ALS, SMA, and DMD that utilize novel gene-delivery and gene-manipulation tools show great promise.

Ms. Yewhalashet is a student in the masters of business and science program, with a concentration in healthcare economics, at Keck Graduate Institute Henry E. Riggs School of Applied Life Sciences, Claremont, Calif. Dr. Davis is professor of practice in clinical and regulatory affairs, Keck Graduate Institute Henry E. Riggs School of Applied Life Sciences.

References

1. Aitken M et al. Understanding neuromuscular disease care. IQVIA [Internet]. Oct 30, 2018. Accessed Mar 1, 2022. https://www.iqvia.com/insights/the-iqvia-institute/reports/understanding-neuromuscular-disease-care.

2. National Institute of Neurological Disorders and Stroke. Neurological diagnostic tests and procedures fact sheet. Updated Nov 15, 2021. Ac-cessed Mar 1, 2022. http://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Neurological-Diagnostic-Tests-and-Procedures-Fact.

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103. SRP-9001. Parent Project Muscular Dystrophy. Accessed August 22, 2022. https://www.parentprojectmd.org/drug-development-pipeline/srp-9001-micro-dystrophin-gene- transfer/

104. Sarepta Therapeutics’ Investigational Gene Therapy SRP-9001 for Duchenne Muscular Dystrophy Demonstrates Significant Functional Improvements Across Multiple Studies | Sarepta Therapeutics, Inc. Accessed August 22, 2022. https://investorrelations.sarepta.com/news-releases/news-release- details/sarepta-therapeutics-investigational-gene-therapy-srp-9001

105. Sarepta Therapeutics, Inc. An Open-Label Safety, Tolerability, and Efficacy Study of Eteplirsen in Patients With Duchenne Muscular Dys-trophy Who Have Completed Study 4658-102.clinicaltrials.gov; 2022. Accessed August 18, 2022. https://clinicaltrials.gov/ct2/show/NCT03985878

106. Sarepta Therapeutics, Inc. An Open-Label Safety, Tolerability, and Pharmacokinetics Study of Eteplirsen in Young Patients With Duchenne Mus-cular Dystrophy Amenable to Exon 51 Skipping. clinicaltrials.gov; 2021. Accessed August 18, 2022. https://clinicaltrials.gov/ct2/show/NCT03218995

107.Sarepta Therapeutics, Inc. A Randomized, Double-Blind, Dose Finding and Comparison Study of the Safety and Efficacy of a High Dose of Eteplirsen, Preceded by an Open-Label Dose Escalation, in Patients With Duchenne Muscular Dystrophy With Deletion Mutations Amenable to Exon 51 Skipping. clinicaltrials.gov; 2022. Accessed August 18, 2022. https://clinicaltrials.gov/ct2/show/NCT03992430

108. Sarepta Therapeutics, Inc. A Phase 2, Two-Part, Multiple-Ascending-Dose Study of SRP-5051 for Dose Determination, Then Dose Ex-pansion, in Patients With .gov/ct2/show/NCT02081625.

110. NS Pharma Inc. A phase II, dose finding study to assess the safety, tolerability, pharmacokinetics, and pharmacodynamics of NS-065/NCNP-01 in boys with Duchenne muscular dystrophy (DMD). ClinicalTrials.gov Identifier: NCT02740972. Updated Dec 7, 2021. Ac-cessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT02740972.

111. NS Pharma Inc. A phase II, open-label, extension study to assess the safety and efficacy of NS-065/NCNP-01 in boys with Duchenne muscular dystrophy (DMD). ClinicalTrials.gov Identifier: NCT03167255. Updated Nov 24, 2021. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT03167255.

112. NS Pharma Inc. A phase 2 open label study to assess the safety, tolerability, and efficacy of viltolarsen in ambulant and non-ambulant boys with Duchenne muscular dystrophy (DMD) compared with natural history controls. ClinicalTrials.gov Identifier: NCT04956289. Updated Feb 1, 2022. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT04956289.

113. NS Pharma Inc. A phase 3 randomized, double-blind, placebo-controlled, multi-center study to assess the efficacy and safety of viltolarsen in ambulant boys with Duchenne muscular dystrophy (DMD). ClinicalTrials.gov Identifier: NCT04060199. Updated Nov 16, 2021. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT04060199.

114. NS Pharma Inc. A phase 3, multi-center, open-label extension study to assess the safety and efficacy of viltolarsen in ambulant boys with Duchenne muscular dystrophy (DMD). ClinicalTrials.gov Identifier: NCT04768062. Updated Nov 16, 2021. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT04768062.

115. Sarepta Therapeutics Inc. A randomized, double-blind, placebo-controlled, dose-titration, safety, tolerability, and pharmacokinetics study followed by an open-label safety and efficacy evaluation of SRP-4045 in advanced-stage patients with Duchenne muscular dystrophy amena-ble to exon 45 skipping. ClinicalTrials.gov Identifier: NCT02530905. Updated May 17, 2021. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT02530905.

116. Sarepta Therapeutics Inc. Long-term, open-label extension study for patients with Duchenne muscular dystrophy enrolled in clinical trials evaluating casimersen or golodirsen. ClinicalTrials.gov Identifier: NCT03532542. Updated Dec 20, 2021. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT03532542.

117. PTC Therapeutics. A phase 2 study of the safety, pharmacokinetics, and pharmacodynamics of ataluren (PTC124®) in patients aged ≥2 to <5 years old with nonsense mutation dystrophinopathy. ClinicalTrials.gov Identifier: NCT02819557. Updated Aug 28, 2020. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT02819557.

118. PTC Therapeutics. Phase 2, non-interventional, clinical study to assess dystrophin levels in subjects with nonsense mutation Duchenne muscular dystrophy who have been treated with ataluren for ≥ 9 months. ClinicalTrials.gov Identifier: NCT03796637. Updated Apr 10, 2020. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT03796637.

119. PTC Therapeutics. An Open-Label Study Evaluating the Safety and Pharmacokinetics of Ataluren in Children From ≥6 Months to <2 Years of Age With Nonsense Mutation Duchenne Muscular Dystrophy. clinicaltrials.gov; 2022. Accessed August 18, 2022. https://clinicaltrials.gov/ct2/show/NCT04336826 120. PTC Therapeutics. An open-label study for previously treated ataluren (PTC124®) pa-tients with nonsense mutation dystrophinopathy. ClinicalTrials.gov Identifier: NCT01557400. Updated Nov 25, 2020. Accessed Feb 21, 2022. https://clinicaltrials.gov/ct2/show/NCT01557400.

121. PTC Therapeutics. An open-label, safety study for ataluren (PTC124) patients with nonsense mutation dystrophinopathy. ClinicalTrials.gov Identifier: NCT01247207. Updated Feb 16, 2022. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT01247207.

122. PTC Therapeutics. A phase 3, randomized, double-blind, placebo-controlled efficacy and safety study of ataluren in patients with non-sense mutation Duchenne muscular dystrophy and open-label extension. ClinicalTrials.gov Identifier: NCT03179631. Updated Feb 8, 2022. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT03179631.

123. Sarepta Therapeutics, Inc. An Open-Label, Systemic Gene Delivery Study Using Commercial Process Material to Evaluate the Safety of and Expression From SRP-9001 in Subjects With Duchenne Muscular Dystrophy (ENDEAVOR). clinicaltrials.gov; 2022. Accessed August 18, 2022. https://clinicaltrials.gov/ct2/show/NCT04626674

124. Sarepta Therapeutics, Inc. Systemic Gene Delivery Phase I/IIa Clinical Trial for Duchenne Muscular Dystrophy Using RAA-Vrh74.MHCK7.Micro-Dystrophin (MicroDys-IV-001). clinicaltrials.gov; 2022. Accessed August 18, 2022. https://clinicaltrials.gov/ct2/show/NCT03375164

125. Sarepta Therapeutics Inc. A multicenter, randomized, double-blind, placebo-controlled trial for Duchenne muscular dystrophy using SRP-9001. ClinicalTrials.gov Identifier: NCT03769116. Updated Dec 2021. Accessed Mar 2, 2022. https://clinicaltrials.gov/ct2/show/NCT03769116.

126. Hoffmann-La Roche. A Two-Part, Seamless, Multi-Center, Randomized, Placebo-Controlled, Double-Blind Study to Investigate the Safety, Tolerability, Pharmacokinetics, Pharmacodynamics and Efficacy of RO7204239 in Combination With Risdiplam (RO7034067) in Ambulant Pa-tients With Spinal Muscular Atrophy. clinicaltrials.gov; 2022. Accessed September 1, 2022. https://clinicaltrials.gov/ct2/show/NCT05115110

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Larry J. Davis, PharmD

Author(s)

Nahomi Yewhalashet

Larry J. Davis, PharmD

Amyotrophic lateral sclerosis

Superoxide dismutase type 1 (SOD1).
Chromosome 9 open reading frame 72 (C9orf72).
Transactive response DNA-binding protein 43 (TARDBP).
Fused in sarcoma (FUS).

Treatment of ALS

Two treatments for ALS are Food and Drug Administration approved: riluzole (Rilutek), approved in 1995, and edaravone (Radicava), approved in 2017.

Gene-based therapy for ALS

Change from baseline in CSF SOD1 protein concentration.¹⁷ Percent reduction in the total SOD1 protein level was much higher in the tofersen-treated group than in the control group (38% more than controls in the faster-progressing population; 26% more than controls in the slower-progressing population).¹⁸
Change from baseline in neurofilament light-chain concentration in plasma.^17,18 Percent reduction in the level of neurofilament light chain was also observed to be higher in the tofersen-treated group than in the control group (67% more than controls in the faster-progressing population and 48% more than controls in the slower-progressing population).¹⁸

Spinal muscular atrophy

Gene-based therapy for SMA

Percentage of motor milestones responders, as determined using Section 2 of the Hammersmith Infant Neurological Examination–Part 2.
Event-free survival (that is, avoidance of combined endpoint of death or permanent ventilation).

Duchenne muscular dystrophy

Therapy for DMD

Gene-based therapy for DMD

Mutation-specific therapeutic approaches, such as exon skipping and nonsense suppression, have shown promise for the treatment of DMD (Table 3^58-79):

ASO-mediated exon skipping allows one or more exons to be omitted from the mutated DMD mRNA.^74,75 Effective FDA-approved ASOs include golodirsen [Vyondys 53], viltolarsen [Viltepso], and casimersen [Amondys 45].⁷⁴
An example of therapeutic suppression of nonsense mutations is ataluren [Translarna], an investigational agent that can promote premature termination codon read-through in DMD patients.⁶⁶

Challenges ahead, but advancements realized

References

Amyotrophic lateral sclerosis

Superoxide dismutase type 1 (SOD1).
Chromosome 9 open reading frame 72 (C9orf72).
Transactive response DNA-binding protein 43 (TARDBP).
Fused in sarcoma (FUS).

Treatment of ALS

Two treatments for ALS are Food and Drug Administration approved: riluzole (Rilutek), approved in 1995, and edaravone (Radicava), approved in 2017.

Gene-based therapy for ALS

Change from baseline in CSF SOD1 protein concentration.¹⁷ Percent reduction in the total SOD1 protein level was much higher in the tofersen-treated group than in the control group (38% more than controls in the faster-progressing population; 26% more than controls in the slower-progressing population).¹⁸
Change from baseline in neurofilament light-chain concentration in plasma.^17,18 Percent reduction in the level of neurofilament light chain was also observed to be higher in the tofersen-treated group than in the control group (67% more than controls in the faster-progressing population and 48% more than controls in the slower-progressing population).¹⁸

Spinal muscular atrophy

Gene-based therapy for SMA

Percentage of motor milestones responders, as determined using Section 2 of the Hammersmith Infant Neurological Examination–Part 2.
Event-free survival (that is, avoidance of combined endpoint of death or permanent ventilation).

Duchenne muscular dystrophy

Therapy for DMD

Gene-based therapy for DMD

Mutation-specific therapeutic approaches, such as exon skipping and nonsense suppression, have shown promise for the treatment of DMD (Table 3^58-79):

ASO-mediated exon skipping allows one or more exons to be omitted from the mutated DMD mRNA.^74,75 Effective FDA-approved ASOs include golodirsen [Vyondys 53], viltolarsen [Viltepso], and casimersen [Amondys 45].⁷⁴
An example of therapeutic suppression of nonsense mutations is ataluren [Translarna], an investigational agent that can promote premature termination codon read-through in DMD patients.⁶⁶

Challenges ahead, but advancements realized

References

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Spinal muscular atrophy: Patient care in the age of genetically targeted therapy

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Sat, 10/15/2022 - 00:15

Author(s)

Kelli Whitlock Burton

In 2016, the U.S. Food and Drug Administration approved nusinersen, the first treatment for spinal muscular atrophy (SMA). Until then, SMA had a mortality rate nearly double that of the general population.¹ Two-thirds of patients were symptomatic within 6 months of birth and, in the absence of mechanical ventilation and other support, had a nearly 100% mortality rate by age 2.²

Five years later, there are three approved treatments for SMA, all of which have been shown to slow or even halt disease progression in many patients. These new therapies, coupled with expanded newborn screening and advancements in optimizing patient care, are changing the natural history of the disease and offering a prognosis that extends well beyond adolescence. Neurologists, whose SMA patient population once consisted almost entirely of children, are now treating more adults with the disease. Indeed, more than half of all people alive with SMA in the United States today are adults, according to Cure SMA.

“Managing SMA used to be clinic follow-ups where we were doing our best supportive care and watching people fall apart before our eyes,” said John Brandsema, MD, a physician and neuromuscular section head at the Children’s Hospital of Philadelphia. “Today, what we see in the vast majority of people is that they are either the same as they were before – which is completely against the natural history of this disease and something to be celebrated – or that people are really better with their function. It totally changes everything in the clinic.”

Among those changes are a more proactive approach to rehabilitation and an even greater emphasis on personalized medicine and multidisciplinary care. But there is also a need for updated treatment guidelines, a new classification system to measure disease severity, specific biomarkers to guide therapy choices, more data on long-term efficacy of existing therapeutics, new medications to complement those therapies, and a deeper understanding of a disease that may have treatment options but still has no cure.

Advances in early diagnosis

Patients with SMA lack a working copy of the survival motor neuron 1 (SMN1) gene, which provides instructions for producing a protein called SMN that is critical for the maintenance and function of motor neurons. Without this protein, motor neurons eventually die, causing debilitating and progressive muscle weakness that affects the ability to walk, eat, and breathe. SMA is rare, affecting about 1 in 10,000 newborns.

In approximately 96% of patients, SMA is caused by homozygous loss of the SMN1 gene. People with SMA have at least one copy of the SMN2 gene, sometimes called a “backup” gene, that also produces SMN protein. However, a single nucleotide difference between SMN2 and SMN1 causes about 90% of the protein produced by SMN2 to be truncated and less stable. Even with multiple copies of SMN2 present, as is the case with many infants with SMA, the amount of functional protein produced isn’t enough to compensate for the loss of SMN1.³

All three approved medications are SMN up-regulators and work to increase the amount of functional SMN protein. Starting these medications early, even before symptoms present, is critical to preserve motor function. Early treatment depends on early diagnosis, which became more widespread after 2018 when SMA was added to the federally Recommended Uniform Screening Panel for newborns. As of July 1, 2022, 47 states have incorporated SMA newborn screening into their state panel, ensuring that 97% of all infants born in the United States undergo SMA screening shortly after birth. Screening in the remaining states – Hawaii, Nevada, and South Carolina – and Washington, D.C. is expected by mid-2023.

SMA newborn screening is a PCR-based assay that detects homozygous SMN1 gene deletion found in about 95% of all people with SMA. The remaining 5% of cases are caused by various genetic mutations that can only be detected with gene sequencing. In these cases, and in children who don’t undergo SMA newborn screening, the disease is usually identified when symptoms are noticed by a parent, pediatrician, or primary care provider. But a study found that in 2018 only 52.7% of pediatricians correctly identified genetic testing as a requirement for a definitive diagnosis of SMA; in 2019, with a larger sample size, that number decreased to 45%.⁴ The lack of awareness of diagnostic requirements for SMA could contribute to delays in diagnosis, said Mary Schroth, MD, chief medical officer for Cure SMA and a coauthor of the study.

“In our world, suspicion of SMA in an infant is an emergency situation,” Dr. Schroth said. “These babies need to be referred immediately and have genetic testing so that treatment can begin as soon as possible.”

Based on the study findings, Dr. Schroth and others with Cure SMA launched a new tool in 2021 designed to help pediatricians, primary care physicians, and parents identify early signs of SMA, so that a referral to a pediatric neurologist happens quickly. Called SMArt Moves, the educational resource features videos and a checklist to help increase early detection in infants who had a negative SMA newborn screening result or did not receive SMA screening at birth.⁵

Who to treat, when, and with which treatment

For many patients, having multiple effective treatment options means that SMA is no longer a fatal disease in early childhood, but one that can be managed into adolescence and adulthood. The question for clinicians is, who do they treat, when, and with which treatment?

Studies have long shown that the number of copies of the backup gene that a patient has is inversely associated with disease severity.⁶ In 2018, a group of SMA experts published a treatment algorithm to help guide decision-making following a positive SMA newborn screening.⁷ The treatment guidelines were updated in 2020 based on clinical trial data for presymptomatic infants, and current recommendations include immediate treatment for infants with two to four copies of the SMN2 gene.⁸ For patients with only one copy of SMN2, most of whom will likely be symptomatic at birth, the guidelines recommend that treatment decisions be made jointly between the clinician and the family.^7,8

Some suggest that the number of SMN2 copies a patient has should also be a factor in determining phenotype, which has started a conversation on the development of a new classification system.⁹ The original classification system for disease severity – Types 0-4 – was based on age of onset and degree of motor function achieved, with Type 0 developing prenatally and being the most severe and Type 4 developing in adulthood. Type 1 is the most common, affecting more than half of all people with SMA, followed by Types 2-4. In 2018, updated consensus care guidelines offered a revised classification system that better reflected disease progression in the age of therapy. The functional motor outcomes include nonsitters (historically Type I), sitters (historically Type 2/3), and walkers (historically Type 3/4).^10,11 These guidelines are a start, but clinicians say more revision is needed.

“Types 1, 2, 3, 4 were based on function – getting to a certain point and then losing it, but now that we can treat this disease, people will shift categories based on therapeutic response or based on normal development that is possible now that the neurologic piece has been stabilized,” Dr. Brandsema said. “We need to completely change our thinking around all these different aspects of SMA management.”

While discussions of a new classification system for SMA are underway, another effort to update treatment recommendations is closer to completion. Led by Cure SMA, a group of about 50 physician experts in the United States and Europe who specialize in SMA are revising guidelines for diagnosis and treatment, the first time the recommendations have been updated since 2018. The updated recommendations, which should be published later this year, will focus on diagnosis and treatment considerations.

“We have three treatments that are available, and there are specific FDA indications for each of those, but it’s not totally clear just how those medications should be used or applied to different clinical situations,” said Dr. Schroth. “We’re in a rapid phase of learning right now in the SMA community, trying to understand how these treatments alter physiology and disease outcomes and how to best use the tools that we now have available to us. In parallel with clinical treatments, we have to be doing the best care we can to optimize the outcomes for those treatments.”

Research advances in 2021

Although all three drugs approved to treat SMA – nusinersen (Spinraza; Biogen), onasemnogene abeparvovec-xioi gene replacement therapy (Zolgensma; Novartis Gene Therapies), and risdiplam (Evrysdi, Genentech/Roche) – are highly effective, there are still unanswered questions and unmet needs. New research findings from 2021 focused on higher dosing, different drug-delivery methods, combination therapy, and complementary therapeutics to address SMA comorbidities.

Higher-dose nusinersen. The first drug approved to treat SMA, nusinersen is an antisense oligonucleotide approved for all ages and all SMA types. It works by altering splicing of the SMN2 gene pre-mRNA to make more complete SMN protein. Given as an intrathecal (IT) injection, four “loading doses” are administered within the first 2 months of treatment, followed by a maintenance dose every 4 months for the duration of the individual’s life.

Reports from patients of waning effects of nusinersen just prior to follow-up treatment have led some clinicians to ask if a higher dose may be needed. A study underway seeks to address that issue.

DEVOTE is a phase 2/3 trial to study the safety and efficacy of high-dose nusinersen in patients with SMA. Preliminary findings reported in 2021 found no adverse events among patients treated with 28 mg of nusinersen for 161-257 days.¹² Another analysis from this trial found that higher doses are associated with greater decrease of plasma phosphorylated neurofilament heavy chain (pNF-H) levels in patients with SMA and may lead to clinically meaningful improvement in motor function beyond that observed with the approved 12 mg dose.¹³ The trial is ongoing.

Another trial, ASCEND, is a phase 3B study assessing higher dose nusinersen in patients previously treated with risdiplam. Recruitment for that trial began in October 2021.

Long-term efficacy and IT administration of SMA therapy. Several studies are looking at the long-term efficacy and alternate routes of administration of onasemnogene abeparvovec and other SMA therapies.

A one-time gene replacement therapy delivered via an IV infusion replaces the function of the missing or nonworking SMN1 gene with a new, working copy of the SMN1 gene. FDA approved in 2019, it is authorized for use in patients with SMA up to 2 years of age.

The latest data from an ongoing, long-term follow-up safety study of onasemnogene abeparvovec, published in May 2021, suggest that the treatment’s effects persist more than 5 years after treatment. Researchers followed 13 infants with symptomatic SMA type 1 since the beginning of the phase 1 clinical trial of the gene transfer therapy. All patients who received the therapeutic dose maintained their baseline motor function, and two of the patients actually improved without other SMN-targeted treatment. At a median 6.2 years after they received treatment, all were alive and none needed permanent ventilation.¹⁴

After a 2-year hold by the FDA, a study of IT administration of onasemnogene abeparvovec is now enrolling patients. Citing concerns from animal studies that IT administration might result in dorsal root ganglia injury, the FDA issued a partial hold on the STRONG trial in 2019. Following positive study results in nonhuman primates, the FDA announced the trial can continue. Novartis is launching a new phase 3 STEER trial to test the drug delivered intrathecally in patients aged 2-18 years with Type 2 SMA. IT administration could allow the gene therapy to be used safely and effectively in more patients with SMA.

Efficacy of risdiplam in more patients. The first oral treatment for SMA was approved by the FDA in 2020. It’s given once per day in patients with SMA of all ages and disease types. The drug increases functional SMN protein production by the SMN2 gene.

A July 2021 publication of the results of the FIREFISH study found that infants with Type I SMA treated with risdiplam for 12 months were significantly more likely to achieve motor milestones, such as sitting without support, compared with untreated infants with Type 1 SMA.¹⁵ Risdiplam is also effective in older patients with Type 2 or 3 SMA, according to results published in December from the SUNFISH clinical trial.¹⁶ Another study, RAINBOWFISH, is studying safety and efficacy at 24 months in presymptomatic infants started on treatment at up to 6 weeks of age.

The efficacy of risdiplam in previously treated patients is the subject of JEWELFISH, an ongoing study in patients 6 months to 60 years with SMA. Preliminary data presented at the 2020 Virtual SMA Research and Clinical Care Meeting suggest treatment with risdiplam led to a median two-fold increase in the amount of blood SMN protein levels after 4 weeks, which was sustained for at least 24 months.¹⁷

Combination therapy. Among the more eagerly awaited results are those from studies of combination therapies, including those that combine approved SMN up-regulators with new non–SMN-targeted therapeutics.

“We’re seeing that while these three approved therapies have dramatic results, especially for infants who are treated presymptomatically, there are still unmet medical needs in those patients, particularly for older teens and adults whose disease may have progressed before they were able to start therapy,” said Jackie Glascock, PhD, vice president of research for Cure SMA.

Of particular interest are studies of myostatin inhibitors, therapeutics that block the production of the protein myostatin. Myostatin acts on muscle cells to reduce muscle growth. Animal studies suggest that inhibiting myostatin increases muscle mass, which could be important in patients with muscle loss due to SMA.

Three experimental myostatin inhibitors are currently in clinical trials. MANATEE is a global phase 2-3 trial that aims to evaluate the safety and efficacy of the antimyostatin antibody GYM329 (RO7204239) in combination with risdiplam. SAPPHIRE is a phase 3 trial of apitegromab (SRK-015) in combination with nusinersen or risdiplam. RESILIANT is a phase 3 trial of tadefgrobep alfa in combination with other treatments.

A trial is underway to study the efficacy and safety of nusinersen in patients with persistent symptoms of SMA after treatment with the gene therapy. The phase 4 study, RESPOND, is enrolling children aged 2-36 months.

What’s needed next

Despite the advances in treatment and patient care, Dr. Brandsema, Dr. Schroth, and Dr. Glascock note that there remain unmet needs in the SMA community in a variety of areas.

Increased focus on adults with SMA. Before nusinersen, treatment of SMA mainly involved treating its symptoms. Many patients stopped seeing their neurologist, relying more heavily on pulmonary care specialists and/or primary care providers to address breathing, nutrition, and mobility problems. “Now with the approval of these treatments, they’re coming back to see their neurologists and are becoming more visible in the SMA community,” Dr. Schroth said.

Despite this re-emergence, a 2020 meta-analysis of studies on adults with SMA found a paucity of data on physical and occupational therapy, respiratory management, mental health care, and palliative care.¹⁸

“There is just so much work we need to do in the area of adult clinical care of SMA.”

Treatment algorithms. While the development of the newborn screening algorithm and revised patient care guidelines are helpful resources, clinicians still face uncertainty when choosing which therapy will work best for their patients. Treatment algorithms that help clinicians figure out what therapy or combination of therapies will offer the best outcomes for individual patients are desperately needed, Dr. Brandsema said.

“Each person’s experience of this disease is so unique to the individual based partly on their genetics and partly on the factors about what got them into care and how compliant they are with everything we’re trying to do to help them,” he said. “Biomarkers would help clinicians create personalized treatment plans for each patient.”

More basic science. While scientists have a good understanding of the SMN gene, there are many unanswered questions about the function of the SMN protein and its relationship to motor neuron loss. SMN is a ubiquitously expressed protein, and its function in other cell types is largely unknown. Despite all of the research advances, there is much basic science left to be done.

“We are strongly advocating to regulatory authorities that these aren’t cures and we need to continue to invest in the basic research,” Dr. Glascock said. “These biological questions that pertain to SMN and its function and expression really drive drug development. I really think that understanding those pathways better will lead us to more druggable targets.”

Two deaths from liver failure linked to spinal muscular atrophy drug

Two children taking the gene therapy drug onasemnogene abeparvovec (Zolgensma, Novartis) for spinal muscular atrophy (SMA) have died from acute liver failure, according to a statement issued by the drug’s manufacturer.

The patients were 4 months and 28 months of age and lived in Russia and Kazakhstan. They died 5-6 weeks after infusion with Zolgensma and approximately 1-10 days after the initiation of a corticosteroid taper.

These are the first known fatal cases of acute liver failure associated with the drug, which the company notes was a known side effect included in the product label and in a boxed warning in the United States.

“Following two recent patient fatalities, and in alignment with health authorities, we will be updating the labeling to specify that fatal acute liver failure has been reported,” the statement reads.

“While this is important safety information, it is not a new safety signal,” it adds.

Rare genetic disorder

SMA is a rare genetic disorder that affects about 1 in 10,000 newborns. Patients with SMA lack a working copy of the survival motor neuron 1 (SMN1) gene, which encodes a protein called SMN that is critical for the maintenance and function of motor neurons.

Without this protein, motor neurons eventually die, causing debilitating and progressive muscle weakness that affects the ability to walk, eat, and breathe.

Zolgensma, a one-time gene replacement therapy delivered via intravenous infusion, replaces the function of the missing or nonworking SMN1 gene with a new, working copy of the SMN1 gene.

The first gene therapy treatment for SMA, it was approved by the U.S. Food and Drug Administration in 2019 for patients with SMA up to 2 years of age. It is also the most expensive drug in the world, costing about $2.1 million for a one-time treatment.

“We have notified health authorities in all markets where Zolgensma is used, including the FDA, and are communicating to relevant healthcare professionals as an additional step in markets where this action is supported by health authorities,” the manufacturer’s statement says.

Studies have suggested that the treatment’s effects persist more than 5 years after infusion.

Clinical trials currently underway by Novartis are studying the drug’s long-term efficacy and safety and its potential use in older patients.

The company is also leading the phase 3 clinical trial STEER to test intrathecal (IT) administration of the drug in patients ages 2-18 years who have type 2 SMA.

That trial began late last year after the FDA lifted a 2-year partial hold on an earlier study. The FDA halted the STRONG trial in 2019, citing concerns from animal studies that IT administration may result in dorsal root ganglia injury. The partial hold was released last fall following positive study results in nonhuman primates.

None of the current trials will be affected by the two deaths reported, according to a Novartis spokesperson.

Kelli Whitlock Burton is a staff writer/reporter for Medscape Neurology and MDedge Neurology.

References

1. Viscidi E et al. Comparative all-cause mortality among a large population of patients with spinal muscular atrophy versus matched controls. Neurol Ther. 2022 Mar;11(1):449-457. doi: 10.1007/s40120-021-00307-7.

2. Finkel RS et al. Observational study of spinal muscular atrophy type I and implications for clinical trials. Neurology. 2014 Aug 26;83(9):810-817. doi: 10.1212/WNL.0000000000000741.

3. Klotz J et al. Advances in the therapy of spinal muscular atrophy. J Pediatr. 2021 Sep;236:13-20.e1. doi: 10.1016/j.jpeds.2021.06.033.

4. Curry M et al. Awareness screening and referral patterns among pediatricians in the United States related to early clinical features of spinal muscular atrophy (SMA). BMC Pediatr. 2021 May;21(1):236. doi: 10.1186/s12887-021-02692-2.

5. SMArt Moves. https://smartmoves.curesma.org/

6. Swoboda KJ et al. Natural history of denervation in SMA: Relation to age, SMN2 copy number, and function. Ann Neurol. 2005 May;57(5):704-12. doi: 10.1002/ana.20473.

7. Glascock J et al. Treatment algorithm for infants diagnosed with spinal muscular atrophy through newborn screening. J Neuromuscul Dis. 2018;5(2):145-158. doi: 10.3233/JND-180304.

8. Glascock J et al. Revised recommendations for the treatment of infants diagnosed with spinal muscular atrophy via newborn screening who have 4 copies of SMN2. J Neuromuscul Dis. 2020;7(2):97-100. doi: 10.3233/JND-190468.

9. Talbot K, Tizzano EF. The clinical landscape for SMA in a new therapeutic era. Gene Ther. 2017 Sep;24(9):529-533. doi: 10.1038/gt.2017.52.

10. Mercuri E et al. Diagnosis and management of spinal muscular atrophy: Part 1: Recommendations for diagnosis, rehabilitation, orthopedic and nutritional care. Neuromuscul Disord. 2018 Feb;28(2):103-115. doi: 10.1016/j.nmd.2017.11.005.

11. Finkel RS et al. Diagnosis and management of spinal muscular atrophy: Part 2: Pulmonary and acute care; medications, supplements and immunizations; other organ systems; and ethics. Neuromuscul Disord. 2018 Mar;28(3):197-207. doi: 10.1016/j.nmd.2017.11.004.

12. Pascual SI et al. Ongoing phase 2/3 DEVOTE (232SM203) randomized, controlled study to explore high-dose nusinersen in SMA: Part A interim results and Part B enrollment update. Presented at MDA Clinical and Scientific Conference 2021, Mar 15-18.

13. Finkel RS et al. Scientific rationale for a higher dose of nusinersen. Presented at 2021 Cure SMA Annual Meeting, Jun 9-11. Abstract P46.

14. Mendell JR et al. Five-year extension results of the phase 1 START trial of onasemnogene abeparvovec in spinal muscular atrophy. JAMA Neurol. 2021 Jul;78(7):834-841. doi: 10.1001/jamaneurol.2021.1272.

15. Darras BT et al. Risdiplam-treated infants with type 1 spinal muscular atrophy versus historical controls. N Engl J Med. 2021 Jul 29;385(5):427-435. doi: 10.1056/NEJMoa2102047.

16. Mercuri E et al. Safety and efficacy of once-daily risdiplam in type 2 and non-ambulant type 3 spinal muscular atrophy (SUNFISH part 2): A phase 3, double-blind, randomised, placebo-controlled trial. Lancet Neurol. 2022 Jan;21(1):42-52. doi: 10.1016/S1474-4422(21)00367-7. Erratum in: Lancet Neurol. 2022 Feb;21(2):e2. doi: 10.1016/S1474-4422(22)00006-0. Correction in: Lancet Neurol. 2022 Mar;21(3):e3. doi: 10.1016/S1474-4422(22)00038-2.

17. Genentech announces 2-year risdiplam data from SUNFISH and new data from JEWELFISH in infants, children and adults with SMA. https://www.curesma.org/genentech-risdiplam-data-conference-2020/

18. Wan HWY et al. Health, wellbeing and lived experiences of adults with SMA: a scoping systematic review. Orphanet J Rare Dis. 2020;15(1):70. doi: 10.1186/s13023-020-1339-3.

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Rett syndrome: Looking to the future and the promise of gene therapy

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Courtney S. Ambrose

Barbara J. Bailus, PhD

The dream of curing genetic disorders has been a persistent but elusive goal, even before the human genome was mapped. Once mapping of the human genome was complete in 2001, an entirely new avenue of potential treatments and cures for genetic diseases and disorders was opened.^1,2

The disorders best suited for targeted gene therapy are monogenic; however, tools and delivery methods for editing the human genome were limited and difficult to apply, until the advent of the CRISPR system in 2012.³ CRISPR (an acronym of clustered regularly interspaced short palindromic repeats) has changed the way in which gene therapy strategies are pursued, with dozens of companies leveraging a variety of platforms to create potentially life-changing therapies for devastating rare diseases and disorders.

One of the rare monogenic disorders that is embracing multiple gene therapy approaches is Rett syndrome, a rare, debilitating neurodevelopmental disorder. In this review, we explore the molecular cause of Rett syndrome, disease presentation, current treatments, ongoing clinical trials, and therapies that are on the horizon.

Underlying molecular cause

Rett syndrome is caused by mutations in, or the absence of, the MECP2 gene, which produces methyl-CpG binding protein 2 (MECP2). The syndrome was first described clinically in 1954 by the Austrian physician Andreas Rett; it would take until 1982 before the disorder was officially named, eponymously, in a seminal paper by Hagberg.⁴ After Hagberg’s characterization, Rett syndrome became the predominant global clinical diagnosis identified among cognitively impaired females, with an incidence of 1 in every 10,000 to 15,000.⁴

In 1999, mutations in, and deletions of, MECP2 were identified as the cause of Rett syndrome.^4,5 MECP2 is located on the X chromosome, in the Xq28 region, making Rett syndrome an X-linked dominant disorder.⁶ Rett syndrome is seen predominantly in females who are mosaic for mutant or deleted MECP2. Random X chromosome inactivation results in some cells expressing the mutant MECP2 allele and other cells expressing the normal functioning MECP2 allele; the percentage of cells expressing the normal allele correlates with the degree of syndrome severity.^7-9

The incidence of Rett syndrome is much lower in males, in whom the syndrome was originally thought to be lethal; many observed male cases are either mosaic or occur in XXY males.^10,11

Approximately 95% of cases of Rett syndrome are due to de novo mutations in MECP2, with a handful of specific mutations and large deletions accounting for more than 85% of cases.¹² The fact that Rett syndrome is monogenic and most cases are caused by, in total, only a handful of mutations or deletions makes the syndrome a promising candidate for gene therapy.

At the molecular level, it has been observed that the MECP2 mutations of Rett syndrome lead to loss of gene function, thus disrupting the ability of the MECP2 nuclear protein to regulate global gene transcription through its binding to methylated DNA sites.¹² A large percentage of these missense and nonsense mutations lead to a truncated or nonfunctional protein.¹²

One of the ways in which MECP2 regulates transcription is as a component of heterochromatin condensates and by separation of heterochromatin and euchromatin.^13-15 It has been observed that the cells of Rett syndrome patients have an altered chromatin state, potentially contributing to transcriptional dysregulation.^16,17 Several mutations observed in Rett syndrome patients occur in crucial domains for heterochromatin condensate formation, which helps explain this cellular phenotype.¹³ Introduction of a engineered “mini” MECP2 in a murine model of Rett syndrome has resulted in partial rescue of heterochromatin condensate formation and transcriptional regulation – fostering the hypothesis that correcting those genetic changes could lead to a potential therapy.¹⁸

Beyond the role of MECP2 in heterochromatin condensate formation, the gene interacts with more than 40 proteins that have diverse roles in cellular function, epigenetic modulation, and neuronal development. This volume of interactions contributes to MECP2 being a global gene regulatory protein that has far-reaching effects on transcriptional regulation across the genome.^19-22

Epigenetic dysregulation has been associated with neurodevelopmental and neuropsychiatric disorders.²³ Both insulin-like growth factor 1 (IGF-1) and brain-derived neurotrophic factor are transcriptional targets of MECP2, and are involved in neuronal differentiation, synaptic function, and neurite outgrowth.¹² This helps explain the neurodevelopmental phenotypes observed in MECP2-mutated patients.

Notably, although Rett syndrome patients experience neurodevelopmental phenotypes at the cellular level, neuronal death is not readily observed. That observation provides hope that an interventional therapy after onset of symptoms might still be of benefit.

Presentation

Early neurotypical development. A hallmark of Rett syndrome is neurotypical physical and mental development until 6 to 24 months of age.

Stagnation is the first stage of the syndrome, involving a small but rapid decline in habitual milestones, such motor and language skills.¹² Subtle signs, such as microcephaly and hypotonia, can also arise at this time but might be missed.²⁴

Rapid regression follows stagnation. Speech and motor delays and impaired gait and breathing occur;^12,25 purposeful hand skills are lost, replaced by repetitive hand-wringing movements that are a hallmark of the syndrome.^12,24 Seizures are observed; they become more common during the next stage.¹²

Plateau. Language advances can be observed, but further deficits are seen in motor skills and hand coordination.¹²

Late motor deterioration stage. Late physical deficits develop, leading to lifelong impairments. The physical deficits observed are the result of severe muscle weakness, usually resulting in wheelchair dependency.¹²

Plateau. Patients then reach a second plateau. Regression stops; deficient physical and cognitive states stabilize and are maintained.²⁵

At all stages of Rett syndrome, the following are observed:

Gastrointestinal problems.
Sleep disturbances.
Abnormal cardiorespiratory coupling.
Greater-than-expected mortality.¹²

Final regression. The patient is fully dependent for the rest of their lifespan, partially due to seizure activity.^26,27

A life-changing diagnosis

A diagnosis of Rett syndrome is life-changing for a patient’s family; access to supportive groups of other patients and their families is extremely beneficial. Two helpful organizations – the Rett Syndrome Research Trust²⁸ and International Rett Syndrome Foundation,²⁹ – offer patient support and community and fund research.

Because X chromosome inactivation is random in Rett syndrome, the individual patient can present with a wide variety of phenotypic combinations – making the patient, and their needs, unique.¹² During stages of regression, patients often experience emotional dysregulation and anxiety, which is attributable to their increasing physical difficulties.³⁰ They often exhibit combinations of uncontrolled movements, including repetitive rocking, scratching, and self-injurious behavior.³⁰ For most, regression subsides after the first 5 years of alternating development and regression; after that, their ultimate symptoms persist for life.²⁵

As patients mature, they need to be monitored for proper nutrition and scoliosis.²⁵ As adults, they are at risk of pneumonia, respiratory distress, status epilepticus, osteopenia, and lack of adequate food or water because of impaired ability to feed.²⁵

The lifespan of Rett syndrome patients has increased, thanks to improvements in health care, advances in technology, and early genetic testing, which allows for earlier diagnosis, intervention, and management of symptoms.

Current treatments

When a female patient presents with regression and loss of milestones, sequencing of MECP2 is performed to verify whether Rett syndrome is the cause, by detecting any of the known mutations. Multiplex ligation-dependent probe amplification is also performed to detect major deletions.²⁵

All available treatments for Rett syndrome are symptomatic; intensive early intervention is practiced.³¹ Multidisciplinary management – medical, psychiatric, and physical – is introduced almost immediately after diagnosis. Following diagnosis, patients are prescribed anti-seizure, sleep, and anxiety medications.³¹ Electroencephalography can be performed to identify seizure type. Neuromuscular blockage drugs can be prescribed to help with gait and stereotypic hand movements.²⁵

Handguards or splints to the elbows can be prescribed by an occupational therapist to improve hand movement.²⁵ Physical therapy can improve mobility; hydrotherapy and hippotherapy have been successful in helping to maintain mobility and muscle support.^32,33 Nutritional management is implemented to control caloric intake and maintain the vitamin D level.³¹ Some patients experience constipation and urinary retention, putting them at risk of nephrolithiasis.

Once the signs and symptoms of Rett syndrome progress, and milestones regress to a certain point, patients need constant, full-time care for the rest of their lives.³⁴ As symptomatic interventions have greatly improved patient outcomes and it has been shown that about 70% can reach adulthood with a potential lifespan of about 50 years.²⁵

Although there is no cure for Rett syndrome and treatments are symptomatic, ongoing studies – both clinical and preclinical – offer promise that treatments will be developed that work at molecular and genetic levels.

Clinical trials

Advances in understanding of Rett syndrome have led to many therapies in clinical trials, several of which show promise.

Trofinetide. One of the most promising targets for downstream therapy, mentioned earlier, is IGF-1, which was the target of a successful phase 3 clinical trial, LAVENDER (sponsored by Acadia Pharmaceuticals).^35,36 This trial studied trofinetide, a synthetic IGF-1 analog that inhibits neuroinflammation, restores glial function, corrects synaptic deficiencies, and regulates oxidative stress response.^12,37,38 Initial results from phase 2 and phase 3 trials indicate improved scores for treated patients in the Rett syndrome Behaviour Questionnaire (RSBQ) and Clinical Global Impression–Improvement (CGI-I) scores, while also showing improvements in the Communication and Symbolic Behavior Scales Developmental Profile Infant–Toddler Checklist–Social composite score.^36,39

The most common adverse events seen with trofinetide were diarrhea and vomiting.

Acadia Pharmaceuticals has filed for approval of a new drug application for trofinetide with the Food and Drug Administration, for which the company has been granted Fast Track Status and orphan drug designations. Most (95%) subjects in the phase 3 LAVENDER trial elected to continue taking trofinetide in the subsequent open-label Lilac and Lilac-2 extension studies.³⁶ A current open-label phase 2/3 trial is recruiting patients 2 to 5 years of age to evaluate trofinetide.⁴⁰ It is expected that, in the near future, this could be a drug given to Rett patients as an FDA-approved treatment.

Blarcamesine. Another small molecule drug, blarcamesine (also known as ANAVEX2-73), a sigma-1 receptor agonist, produced promising results in phase 2 clinical trials in adult Rett syndrome patients. The drug is in a phase 2/3 clinical trial for pediatric Rett syndrome patients (sponsored by Anavex Life Sciences).^41-43

Phase 2 results indicated statistically significant and clinically meaningful improvement in RSBQ and CGI-I scores with blarcamesine. Improvement was initially observed within 4 weeks after the start of treatment and was sustained throughout the study. The drug was shown to be well tolerated, with minimal adverse effects; no serious adverse events were recorded. These results were observed in adult patients, demonstrating that improvements in Rett syndrome are possible even after regression.

Blarcamesine activates the sigma 1 receptor, which is pivotal to restoring cellular homeostasis and restoring neuroplasticity – deficiencies of which have been linked to autophagy and glutamate toxicity. The drug has also been explored as a potential treatment for other neurological disorders.^44-47 Improvements in blarcamesine-treated patients further correlated with lower levels of glutamate in cerebrospinal fluid, which is a Rett syndrome biomarker, supporting the proposition that behavioral improvements were due to drug intervention.^48,49 The phase 2 trial was modified into a phase 3 trial and additional endpoints were added.^41-43

All patients in the phase 2 adult trial elected to continue in the extension study.

Based on these promising data, Anavex is pursuing an approval pathway for adult patients, while continuing dosage optimization phase 2/3 trials and recruitment for a pediatric trial.^42,43

Is the future about gene therapy?

TSHA-102 (miniMECP2). Taysha Gene Therapies is developing a promising gene therapy, TSHA-102, for Rett syndrome, and is aiming to begin phase 1/2 clinical trials in 2022.⁵⁰ The technology for this therapy relies on the delivery of a fragment of MECP2 (known as miniMECP2), which is regulated by a built-in microRNA regulator (miR-responsive auto-regulatory element, or miRARE) to help ameliorate MECP2 dosage toxicity. (Overexpression of MECP2 is toxic to neurons, which has made traditional [so to speak] gene replacement therapy difficult in Rett syndrome: Levels of MECP2 need to be tightly regulated, and the Taysha microRNA technology regulates levels of miniMECP2, thus reducing toxicity.)

The Taysha microRNA technology has yielded promising results in mouse studies for Rett syndrome; results indicate a lengthening of lifespan and delayed onset of gait abnormalities.⁵¹ TSHA-102 is in the preclinical stage but offers promise that it will be the first gene therapy for Rett syndrome to enter clinical trials.

As the field of gene therapy advances, several promising technologies are on the horizon that could potentially have disease-altering impacts on Rett syndrome. These therapies are divided into two broad categories: those at the gene level and those at the transcription and protein level. A few of these approaches are highlighted below.

Gene replacement involves adding a full or partial copy of MECP2 to neuronal cells. This type of therapy presents challenges, from delivery of the new gene to dosage concerns, because MECP2 can be toxic if overexpressed.^52-54 Groundbreaking work was done in mouse models involving truncated MECP2, exhibiting phenotypic rescue and validating the gene-replacement approach.¹⁸ This strategy is being pursued by Neurogene, which has a uinique technology that allows for tuning of the gene’s expression to get the correct protein levels in the patient. Promising data was presented this year at the American Society of Gene and Cell Therapy conference.⁵⁵

Early gene replacement therapy studies also laid the foundation for the minMECP2 and microRNA approach being used by Taysha Gene Therapies (discussed above).⁵¹

“Correcting” DNA mutations. A different approach at the genetic level involves “correcting” mutations in MECP2 at the DNA level. This is possible because, in a large subset of Rett syndrome patients who have the same missense or nonsense mutations, by using CRISPR, a gene editing tool (discussed above) a single base pair can be corrected.^56,57 Previous research, in a Rett syndrome-model of induced pluripotent stem cells, showed that this type of editing is possible – and effective.⁵² An approach with particular promise involves use of a class of CRISPR proteins known as base editors that are able to specifically alter a single base of DNA.⁵⁷ The technique has the potential to address many of the mutations seen in Rett syndrome; research on this type of technology is being pursued by Beam Therapeutics, and has the potential to impact Rett syndrome.⁵⁸

Another promising “correction” approach is exonic editing, in which a much larger section of DNA – potentially, exons 3 and 4, which, taken together, comprise 97% of known MECP2 mutations seen in Rett syndrome – are replaced.⁵⁹

In both CRISPR and exonic editing therapeutic approaches, endogenous levels of MECP2 expression would be maintained. Of note, both approaches are being pursued for use in treating other genetic disorders, which provides a boost in scaling-up work on addressing safety and efficacy concerns that accompany gene-editing approaches.⁵⁸One advantage to the DNA correction approach is that is has the potential to be a “one-and-done” treatment.

“Correcting” RNA. Beyond directly editing DNA, several therapeutic approaches are exploring the ability to edit RNA or to provide the protein directly to cells as enzyme replacement therapy. Such an RNA correction strategy leverages a technology that takes advantage of cells’ natural RNA editor, known as adenosine deaminase acting on RNA (ADAR), which corrects errors in cells’ RNA by providing specific guides to the cell. ADAR can be targeted to fix mutations in the MECP2 RNA transcript, resulting in a “corrected” MECP2 protein.^60,61 This technology has delivered promising proof-of-concept evidence in cells and in murine models, and is in the therapeutic pipeline at VICO Therapeutics.⁶²

Shape Therapeutics has also leveraged ADAR to “correct” mutated RNA; Rett syndrome is among the top priorities in the company’s pipeline.

Worth noting is that there are several advantages to the “correction” approach:

Leveraging internal repair mechanisms minimizes the immune response.
The flexibility of correction means that it can be used to address many of the mutations that cause Rett syndrome.⁶³

Enzyme replacement therapy, in which the MECP2 protein produced by MECP2 would be directly replaced, is being explored in Rett syndrome patients. This technology has been used successfully in Pompe disease; however, Rett syndrome presents its own challenge because MECP2 needs to be delivered to the brain and neuronal cells.⁶⁴

Where does this work stand? The technologies described in this section are in preclinical stages of study. Nonetheless, it is expected that several will enter human clinical trials during the next 5 years.

Conclusion

A diagnosis of Rett syndrome is a life-altering event for patients and their family. But there is more hope than ever for effective therapies and, eventually, a cure.

Multiple late-stage clinical trials in progress are demonstrating promising results from therapeutic products, with minimal adverse events. Remarkably, these interventions have delivered improvements to adult patients after regression has stabilized. With rapid progress being made in the field of gene therapy, several technologies for which are focused on Rett syndrome, a hopeful picture is emerging: that therapeutic intervention will be possible before regression, thus effectively treating and, potentially, even curing Rett syndrome.

The landscape is broadening. Add to this hope for approved therapies is the fact that Rett syndrome isn’t the only target being pursued with such strategies; in fact, researchers in the larger field of neurodevelopmental disorder study are working together to find common solutions to shared challenges – from how therapies are designed and delivered to how toxicity is minimized. Much of what is being explored in the Rett syndrome field is also under investigation in other neurodevelopmental syndromes, including Angelman, Prader-Willi, chromosome 15q11.2-13.1 duplication (dup15q), and Fragile X syndrome. This kind of parallel investigation benefits all parties and optimizes a treatment platform so that it can be applied across more than a single disorder.

Like many monogenic disorders, Rett syndrome is entering an exciting stage – at which the words “treatment” and “cure” can be spoken with intent and vision, not just wide-eyed optimism. These words portend real promise for patients who carry the weight of a diagnosis of Rett syndrome, and for their families.

Ms. Ambrose is a student in the master’s of science in human genetics and genomic data analytics program, Keck Graduate Institute, Claremont, Calif. Dr. Bailus is an assistant professor of genetics, Keck Graduate Institute. The authors report no conflict of interest related to this article.

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34. Ip JPK et al. Rett syndrome: Insights into genetic, molecular and circuit mechanisms. Nat Rev Neurosci. 2018 Jun;19(6):368-82. doi: 10.1038/s41583-018-0006-3.

35. Acadia Pharmaceuticals Inc. Study of trofinetide for the treatment of girls and women with Rett syndrome (LAVENDER™). ClinicalTrials.gov identifier: NCT04181723. Updated Feb 17, 2022. Accessed Feb 23, 2022. https://clinicaltrials.gov/ct2/show/NCT04181723.

36. Acadia Pharmaceuticals announces positive top-line results from the pivotal phase 3 LAVENDER trial of trofinetide in Rett syndrome. Press release. Acadia Pharmaceuticals Inc. Dec 6, 2021. Accessed Feb 23, 2022. https://ir.acadia-pharm.com/news-releases/news-release-details/acadia-pharmaceuticals-announces-positive-top-line-results-1.

37. Copping NA et al. Emerging gene and small molecule therapies for the neurodevelopmental disorder Angelman syndrome. Neurotherapeutics. 2021 Jul;18(3):1535-47. doi: 10.1007/s13311-021-01082-x.

38. Riikonen R. Insulin-like growth factors in the pathogenesis of neurological diseases in children. Int J Mol Sci. 2017 Sep;18(10):2056. doi: 10.3390/ijms18102056.

39. Glaze DG et al; Rett 002 Study Group. Double-blind, randomized, placebo-controlled study of trofinetide in pediatric Rett syndrome. Neurology. 2019 April 16;92(16):e1912-e1925. doi: 10.1212/WNL.0000000000007316.

40. Acadia Pharmaceuticals Inc. An open-label study of trofinetide for the treatment of girls two to five years of age who have Rett syndrome (DAFFODIL™). ClinicalTrials.gov Identifier: NCT04988867. Updated Jan 24, 2022. Accessed Feb 23, 2022. https://clinicaltrials.gov/ct2/show/NCT04988867.

41. Anavex Life Sciences announces ANAVEX®2-73 meets primary and secondary endpoints in clinical trial. Press release. Anavex Life Sciences Corp. Dec 15, 2020. Accessed Feb 23, 2022. http://www.anavex.com/post/anavex-life-sciences-announces-anavex-2-73-meets-primary-and-secondary-endpoints-in-clinical-trial.

42. Anavex Life Sciences Corp. ANAVEX2-73 study in patients with Rett syndrome (AVATAR). ClinicalTrials.gov Identifier: NCT03941444. Updated Jan 27, 2022. Accessed Feb 23, 2022. https://clinicaltrials.gov/ct2/show/NCT03941444.

43. Anavex Life Sciences Corp. ANAVEX2-73 study in pediatric patients with Rett syndrome (EXCELLENCE). ClinicalTrials.gov Identifier: NCT04304482. Updated Sep 28, 2021. Accessed Feb 23, 2022. http://www.clinicaltrials.gov/ct2/show/NCT04304482.

44.Christ MG et al. The Sigma-1 receptor at the crossroad of proteostasis, neurodegeneration, and autophagy. Trends Neurosci. 2020 Feb;43(2):79-81. doi: 10.1016/j.tins.2019.12.002.

45. Kaufmann WE et al. ANAVEX®2-73 (blarcamesine), a sigma-1 receptor agonist, ameliorates neurologic impairments in a mouse model of Rett syndrome. Pharmacol Biochem Behav. 2019 Dec;187:172796. doi: 10.1016/j.pbb.2019.172796.

46. Brimson JM et al. Dipentylammonium binds to the sigma-1 receptor and protects against glutamate toxicity, attenuates dopamine toxicity and potentiates neurite outgrowth in various cultured cell lines. Neurotox Res. 2018 Aug;34(2):263-72. doi: 10.1007/s12640-018-9883-5.

47. Kourrich S et al. The sigma-1 receptor: roles in neuronal plasticity and disease. Trends Neurosci. 2012 Dec;35(12):762-71. doi: 10.1016/j.tins.2012.09.007.

48. Lappalainen R, Riikonen RS. High levels of cerebrospinal fluid glutamate in Rett syndrome. Pediatr Neurol. 1996 Oct;15(3):213-6. doi: 10.1016/s0887-8994(96)00218-4.

49. Hamberger A et al. Elevated CSF glutamate in Rett syndrome. Neuropediatrics. 1992;23(4):212-3. doi: 10.1055/s-2008-1071344.

50. Inacio P. FDA acts to support development of potential gene therapy, TSHA-102. Rett Syndrome News [Internet]. Oct 16, 2020. Accessed Feb 23, 2022. https://rettsyndromenews.com/2020/10/16/fda-grants-orphan-drug-rare-pediatric-disease-status-to-tsha-102-potential-rett-gene-therapy.

51. Sinnett SE et al. Engineered microRNA-based regulatory element permits safe high-dose miniMECP2 gene therapy in Rett mice. Brain. 2021 Nov 29;144(10):3005-19. doi: 10.1093/brain/awab182.

52. Le TTH et al. Efficient and precise CRISPR/Cas9-mediated MECP2 modifications in human-induced pluripotent stem cells. Front Genet. 2019 Jul 2;10:625. doi: 10.3389/fgene.2019.00625.

53. Koerner MV et al. Toxicity of overexpressed MeCP2 is independent of HDAC3 activity. Genes Dev. 2018;32(23-24):1514-24. doi: 10.1101/gad.320325.118.

54. Heckman LD et al. Rett-causing mutations reveal two domains critical for MeCP2 function and for toxicity in MECP2 duplication syndrome mice. Elife. 2014;3:e02676. doi: 10.7554/eLife.02676.

55. Neurogene announces new development program in Rett syndrome utilizing novel EXACT technology platform [Internet]. Accessed Aug 12, 2022. https://www.neurogene.com/press-releases/neurogene-announces-new-development-program-in-rett-syndrome-utilizing-novel-exact-technology-platform/

56. Anzalone AV et al. Genome editing with CRISPR-Cas nucleases, base editors, transposases and prime editors. Nat Biotechnol. 2020 Jul;38(7):824-44. doi: 10.1038/s41587-020-0561-9.

57. Gaudelli NM, Komor AC, Rees HA, et al. Programmable base editing of A●T to G●C in genomic DNA without DNA cleavage. Nature. 2017 Nov 23;551(7681):464-71. doi: 10.1038/nature24644.

58. Coenraads M. How RSRT is driving the search for a Rett cure. Rett Syndrome Research Trust [Internet]. Dec 7, 2021. Accessed Feb 23, 2022. https://rettnews.org/articles/how-rsrt-is-driving-the-search-for-a-rett-cure.

59. Cutting-edge technologies to repair the underlying mutations that cause Rett. Rett Syndrome Research Trust [Internet]. Updated Nov 3, 2021. Accessed Feb 23, 2022. https://reverserett.org/research/cures/gene-editing.

60. Sinnamon JR et al. In vivo repair of a protein underlying a neurological disorder by programmable RNA editing. Cell Rep. 2020 Jul 14;32(2):107878. doi: 10.1016/j.celrep.2020.107878.

61. Sinnamon JR et al. Site-directed RNA repair of endogenous Mecp2 RNA in neurons. Proc Natl Acad Sci U S A. 2017 Oct 31;114(44):E9395-E9402. doi: 10.1073/pnas.1715320114.

62. Pipeline. VICO Therapeutics [Internet]. Updated Nov 5, 2021. Accessed Feb 23, 2022. https://vicotx.com/pipeline.

63. Therapeutics platform. Shape Therapeutics [Internet]. Updated Feb 20, 2021. Accessed Feb 23, 2022.

https://live-shapetx.pantheonsite.io/therapeutics-platform.

64. Koeberl DD et al. Glycogen storage disease types I and II: Treatment updates. J Inherit Metab Dis. 2007 Apr;30(2):159-64. doi: 10.1007/s10545-007-0519-9.

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Barbara J. Bailus, PhD

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Barbara J. Bailus, PhD

Underlying molecular cause

Presentation

Early neurotypical development. A hallmark of Rett syndrome is neurotypical physical and mental development until 6 to 24 months of age.

Gastrointestinal problems.
Sleep disturbances.
Abnormal cardiorespiratory coupling.
Greater-than-expected mortality.¹²

Final regression. The patient is fully dependent for the rest of their lifespan, partially due to seizure activity.^26,27

A life-changing diagnosis

Current treatments

Clinical trials

Advances in understanding of Rett syndrome have led to many therapies in clinical trials, several of which show promise.

Is the future about gene therapy?

Leveraging internal repair mechanisms minimizes the immune response.
The flexibility of correction means that it can be used to address many of the mutations that cause Rett syndrome.⁶³

Conclusion

A diagnosis of Rett syndrome is a life-altering event for patients and their family. But there is more hope than ever for effective therapies and, eventually, a cure.

References

Underlying molecular cause

Presentation

Early neurotypical development. A hallmark of Rett syndrome is neurotypical physical and mental development until 6 to 24 months of age.

Gastrointestinal problems.
Sleep disturbances.
Abnormal cardiorespiratory coupling.
Greater-than-expected mortality.¹²

Final regression. The patient is fully dependent for the rest of their lifespan, partially due to seizure activity.^26,27

A life-changing diagnosis

Current treatments

Clinical trials

Advances in understanding of Rett syndrome have led to many therapies in clinical trials, several of which show promise.

Is the future about gene therapy?

Leveraging internal repair mechanisms minimizes the immune response.
The flexibility of correction means that it can be used to address many of the mutations that cause Rett syndrome.⁶³

Conclusion

A diagnosis of Rett syndrome is a life-altering event for patients and their family. But there is more hope than ever for effective therapies and, eventually, a cure.

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The paradox of Pompe disease

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Author(s)

Jennie Smith

Until 2006, when a breakthrough therapy first made treatment possible, Pompe disease was a little-known metabolic myopathy fatal to infants. Those with later-onset disease experienced progressive, often severe disability into adulthood.

In this rare autosomal recessive disorder, which occurs in approximately one in 40,000 births worldwide, a deficiency or absence of the enzyme acid alpha-glucosidase causes glycogen to build up in the lysosomes of cells. While many tissues are affected, skeletal and cardiac muscle see the earliest involvement, with muscle hypotonia, cardiomyopathy, and breathing difficulties (mainly due to diaphragm weakness) comprising the hallmark symptoms of the infantile form. Muscle weakness and progressive respiratory failure are prominent in later-onset disease.

The spectrum of severity and age of onset in Pompe disease is linked to combinations of mutations on the GAA gene, some of which destroy the body’s ability to produce acid alpha-glucosidase whereas others merely hamper it. Less enzyme produced in the body generally corresponds with more severe disease activity.

The most severe end of the disease spectrum, or “classic infantile Pompe disease,” presents at birth and is recognized in early infancy. Until treatment with enzyme replacement therapy (ERT) became available, patients usually died of cardiorespiratory failure within their first year of life. With therapy, patients have survived into their 20s and beyond. Late-onset disease is a far broader category in which patients can present at any time from their first year, including into middle age.

The emergence in 2006 of alglucosidase alfa (Lumizyme, Sanofi Genzyme), an ERT used long-term to improve survival and slow progression in children and adults, resulted in a boom of research interest, a push to timelier diagnosis, and – with patients living longer – a more thorough understanding of the natural history of Pompe disease. In addition to the usual clinical picture of progressive muscle weakness, difficulty breathing, and cardiomyopathy, investigators are seeing nervous system involvement in patients with Pompe disease.

A patient with Pompe, especially one with late-onset disease, may be diagnosed and even managed by his or her neurologist. To learn more, Neurology Reviews talked to two global experts in Pompe disease: Priya Kishnani, MD, of Duke University in Durham, N.C., and Antonio Toscano, MD, of the University of Messina, in Messina, Italy.

Diagnosis: Still room to improve

“Most neurologists will encounter a patient with Pompe disease,” said Dr. Kishnani, who has been working with Pompe for her entire career as a pediatrician and medical geneticist, treating patients of all ages and disease phenotypes.

“In newborns, diagnosis is more straightforward, because you’ve got an enlarged heart,” she said. And thanks to efforts of researchers like Dr. Kishnani and Pompe advocacy groups, Pompe disease is now a part of the RUSP (Recommended Uniform Screening Panel) for newborns; currently 28 U.S. states are screening for Pompe disease.

“The challenge really is for the later-onset cases, which are 80% of all cases,” Dr. Kishnani said.

Previously, muscle biopsies were the first step toward diagnosis. Dried blot spot assays to detect enzyme deficiency have since become the standard, along with other biochemical tests. Confirmation of the diagnosis is through gene sequencing panels to detect GAA mutations.

“Now that there is a treatment for Pompe disease and the availability of blood-based testing, many previously undiagnosed patients with limb girdle weakness are evaluated and the diagnostic odyssey ends,” Dr. Kishnani said. “But there is still a diagnostic delay, and many cases remain undiagnosed.”

Routine blood tests for creatine kinase and for liver enzymes can help point to Pompe disease. But elevated liver enzymes are often misinterpreted. “It’s about the ratios,” Dr. Kishnani said. “ALT is usually much more elevated if it is coming from a liver cause, and AST is usually higher than ALT if it is coming from muscle. But patients often end up getting a liver biopsy due to so-called elevated liver enzymes. As the workup continues, it is often later recognized that the source of the elevated enzymes is muscle involvement, and a referral to the geneticist or neurologist is made. Only then is appropriate testing to confirm a diagnosis initiated.”

Dr. Toscano, a neurologist who specializes in Pompe disease and other myopathies and who has published on tools for diagnosing late-onset Pompe disease,¹ said that clinicians should be vigilant when evaluating any patient with limb girdle weakness and elevated creatine kinase (CK) – “especially if the CK is under 2,000,” he said, “because it is very rare that patients with Pompe disease have a more elevated CK than that.”

“Elevated CK, myalgia, and exercise intolerance” should prompt clinicians to suspect Pompe disease in a patient of any age, Dr. Toscano said. “When you come across this, you should be very persistent and get to the end of the story.”

Dr. Toscano noted that the blood spot assay, while an important early step, is not fully diagnostic, “because you can have false positives.” The molecular GAA assay is used to confirm Pompe disease. But detecting pathogenic variants on the GAA gene – of which there are more than 500 – can be more complicated than it sounds. Whereas two mutations are required for Pompe disease, sometimes only one can be detected. Dr. Toscano said he also treated some patients for Pompe with only one known mutation but with unequivocal clinical and biochemical aspects of Pompe disease.

While delays in diagnosis for late-onset Pompe disease remain significant -- between 5 and 6 years on average for older patients, and up to 20 years for those with pediatric onset – both Dr. Kishnani and Dr. Toscano said they perceive them to be improving. With McArdle disease, another inherited glycogen storage disorder that is more common than Pompe disease but for which there is no treatment, “the delay is nearly 12 years,” Dr. Toscano said.

ERT: The sooner the better

Enzyme replacement therapy is indicated for all patients with Pompe disease. Currently two are commercially available: alglucosidase alfa (Lumizyme, Sanofi Genzyme), indicated for all forms of Pompe disease, and avalglucosidase alfa-ngpt (Nexviazyme, Sanofi Genzyme), approved in 2021 for later-onset Pompe, though its indications have yet to be fully defined.

The semimonthly infusions represent, to date, the only disease-modifying therapies commercially available. Enzyme replacement therapy can reverse cardiac damage seen in infants and allow them to meet developmental milestones previously unthinkable. In adults, it can slow progression, though many treated patients will still develop chronic disability and require a wheelchair, respiratory support, or both. “The phenotype of the patients we are seeing today is not as involved as it was prior to enzyme therapy,” said Dr. Kishnani, who was part of the research team that developed ERT and launched the first clinical trials. “This is across the disease spectrum.”

But optimal management means more than just getting a patient on therapy fast, Dr. Kishnani said.

“Very often the thinking is if the patient is on ERT, we’ve done right by the patient. Aspects we don’t look at enough include: Are we monitoring these patients well? Are patients being followed by a multidisciplinary team that includes cardiology, physical therapy, and pulmonary medicine? Are we doing appropriate musculoskeletal assessments? They might have sleep hypoventilation. The BiPap settings may not be correct. Or they have not been assessed for antibodies,” she said.

Many infants with severe phenotypes, notably those who produce no enzyme naturally, will develop immune reactions to the exogenous enzyme therapy. High antibody titers also have been seen and are associated with poor therapeutic response. While this is very clear in the infantile setting, late-onset patients also develop antibodies in response to ERT. In one study in 64 patients,² Dr. Toscano and his colleagues saw that antibodies may affect clinical response during the first 3 years of treatment, while a small study³ by Dr. Kishnani’s group saw clinical decline associated with high antibody titers in patients with late-onset disease.

While the relationship of specific titers to therapeutic response remains unclear, it is important to consider antibodies, along with other factors, in the monitoring of patients with Pompe disease. “We need to always ask, if a patient is falling behind, what could be the reason?” Dr. Kishnani said. “These are the things we as clinicians can do to improve or enhance the impact of ERT.”

Dr. Toscano noted that a common misconception about late-onset Pompe disease is that cardiac manifestations are minimal or absent, whereas as many as about 20% of patients will have heart problems and need to be carefully monitored.

Neurological manifestations

With patients surviving longer on ERT, researchers have been able to develop a deeper understanding of the natural history of Pompe disease. Increasingly, they are seeing it as a multisystem disease that includes central nervous system involvement.

“Is Pompe an overt neurodegenerative disease? I would say no,” Dr. Kishnani said. “But there is a neurological component that we’ve got to understand and follow more.”

Glycogen accumulation, she noted, has been found in anterior horn cells, motor neurons, and other parts of the brain. “We have been doing MRIs on children with infantile Pompe, and we have seen some white matter hyperintensities. The clinical significance of this finding is still emerging. Sometimes it is present, but the child is cognitively intact. We have had college graduates who have white matter hyperintensities. So putting it in context will be important. But we know that glycogen is ubiquitous, and autopsy studies have shown that it is present in the brain.”

In recent years, Dr. Toscano’s group has investigated neurovascular complications of Pompe in late-onset patients. “This was something that really surprised us because for several years we have investigated mainly heart, muscle, or respiratory manifestations of the disease, but the central nervous system was really neglected,” he said.

“Occasionally we did some brain MRIs and we found in even young patients some ischemic areas. We thought this was related to slowed circulation – that blood vessels in these patients are weak because they are impaired by glycogen accumulation.” Dr. Toscano and his colleagues followed that observation with a study of late-onset patients,⁴ in which they found that more than half had cerebrovascular abnormalities. “Even in, say, patients 30 to 35 years old we saw this – it’s unusual to have a vascular disorder at that age.”

Dr. Toscano and his colleagues also reported cerebral aneurysms⁵ in patients with Pompe disease and have recommended that clinicians conduct MRI or cerebral angiograms on patients as part of routine follow-up. Blood pressure in Pompe patients should be carefully watched and managed with antihypertensive medication as needed, he said.

Part of the problem is that the proteins in ERT are not able to cross the blood-brain barrier, Dr. Toscano noted, adding that researchers are investigating other treatments that can.

Pompe disease as a research model

The successful development of ERT for Pompe disease marked a boom in research interest into not just Pompe – for which several experimental therapies are currently in the pipeline – but for other myopathies and glycogen storage disorders.

“I think that Pompe has served as a template both as a muscle disease and a lysosomal storage disease, and so some of our learnings from Pompe have been applied across different diseases,” Dr. Kishnani said.

Studies in spinal muscular atrophy, for example, “in some ways mirrored what was done for Pompe – treatment trials were initiated in babies at the most severe end of the disease population with infantile disease, and used similar clinical trial endpoints,” Dr. Kishnani said. “Even for the later-onset end of the spectrum, the endpoints we used in Pompe for muscle strength and function have been relevant to many other neuromuscular disorders.”

Pompe disease research also ushered in a new appreciation of immune responses in protein replacement therapies, Dr. Kishnani noted.

“In the field today, you hear the term cross-reactive immunological material, or CRIM, all the time,” she said. “But when we first started talking about it in the space of Pompe disease, there was a lot of scientific debate about what the significance of CRIM-negative status was in relationship to the risk for development of high and sustained antibody titer and a poor clinical response. To understand this involved a lot of going back to the data and digging into the small subset of nonresponders. One of the powers of rare disease research is that every patient matters, and it’s important to understand what’s going on at the patient level rather than just the group data level.”

A robust pipeline

The decade and a half since the advent of ERT has seen what Dr. Toscano described as “an explosion of interest” in Pompe disease.

“We’re seeing an extraordinary number of papers on everything from clinical, biomarkers, genetics, and rehabilitation – this disease is now considered from every point of view, and this is very important for patients,” Dr. Toscano said. Alongside this has come industry interest in this rare disease, with several companies investigating a range of treatment approaches.

The existence of a treatment, “while not perfect,” he said, “has interested the patient associations and doctors to try and improve service to patients. Patients with Pompe disease are well attended, probably more so than patients with degenerative disorders in which there is no therapy.”

Last year the second ERT, avalglucosidase alfa (Nexviazyme, Sanofi Genzyme) was approved by the U.S. Food and Drug Administration to treat late-onset Pompe disease. The drug, currently being investigated in infants as well, was designed to improve the delivery of the therapeutic enzyme to muscles and enhance glycogen clearance, and results from ongoing trials suggest some functional and clinical benefit over standard ERT.

Other drugs in development for Pompe disease include substrate reduction therapies, which aim to reduce the storage of glycogen in cells, and therapies that improve residual function of mutant GAA enzyme in the body. These and other therapies in development have the potential to modify nervous system manifestations of Pompe disease.⁶

Because a single gene is implicated in Pompe disease, it has long been considered a good candidate for gene therapies that prompt the body to make stable enzyme. Seven companies are now investigating gene therapies in Pompe disease.⁷ Some of these deliver to skeletal muscles and others aim for the liver, where proteins are synthesized and secreted and adverse immune responses might be more easily mitigated. Other gene therapies use an ex vivo approach, removing and replacing cells in bone marrow.

Dr. Kishnani’s research group at Duke University is leading a small clinical trial in late-onset patients of a GAA gene transfer to the liver using adeno-associated virus (AAV) vectors.⁸

“We have started AAV gene therapy trials in in adults with Pompe disease and will later evaluate children because ERT is available as a standard of care, and so from a safety perspective this makes the most sense,” Dr. Kishnani said. “We do have challenges in the field of gene therapy, but I think if we are able to overcome the immune responses, and … to treat at a lower dose, there’s a very good pathway forward.”

Dr. Toscano and Dr. Kishnani have received reimbursement from Sanofi and other manufacturers for participation on advisory boards and as speakers.

Jennie Smith is a freelance journalist and editor specializing in medicine and health.

References

1. Musumeci O, Toscano A. Diagnostic tools in late onset Pompe disease (LOPD). Ann Transl Med. 2019 Jul;7(13):286. doi: 10.21037/atm.2019.06.60.

2. Filosto M et al. Assessing the role of anti rh-GAA in modulating response to ERT in a late-onset Pompe disease cohort from the Italian GSDII Study Group. Adv Ther. 2019 May;36(5):1177-1189. doi: 10.1007/s12325-019-00926-5.

3. Patel TT et al. The impact of antibodies in late-onset Pompe disease: A case series and literature review. Mol Genet Metab. 2012 Jul;106(3):301-9. doi: 10.1016/j.ymgme.2012.04.027.

4. Montagnese F et al. Intracranial arterial abnormalities in patients with late onset Pompe disease (LOPD). J Inherit Metab Dis. 2016 May;39(3):391-398. doi: 10.1007/s10545-015-9913-x.

5. Musumeci O et al. Central nervous system involvement in late-onset Pompe disease: Clues from neuroimaging and neuropsychological analysis. Eur J Neurol. 2019 Mar;26(3):442-e35. doi: 10.1111/ene.13835.

6. Edelmann MJ, Maegawa GHB. CNS-targeting therapies for lysosomal storage diseases: Current advances and challenges. Front Mol Biosci. 2020 Nov 12;7:559804. doi: 10.3389/fmolb.2020.559804

7. Ronzitti G et al. Progress and challenges of gene therapy for Pompe disease. Ann Transl Med. 2019 Jul;7(13):287. doi: 10.21037/atm.2019.04.67.

8. Kishnani PS, Koeberl DD. Liver depot gene therapy for Pompe disease. Ann Transl Med. 2019 Jul;7(13):288. doi: 10.21037/atm.2019.05.02.

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Diagnosis: Still room to improve

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A robust pipeline

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Diagnosis: Still room to improve

ERT: The sooner the better

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Health care providers should have higher suspicion for rare diseases

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The number of cataloged rare diseases continues to grow every day. According to the National Human Genome Research Institute, more than 6,800 rare diseases have been identified and between 25 million and 30 million Americans are living with rare diseases today.

Rare diseases have collectively emerged as a unique field of medicine with an “entirely new generation of conditions,” said Marshall L. Summar, MD, chief of the division of genetics and metabolism at Children’s National Hospital in Washington, DC. He places the number of rare diseases closer to 8,000, and said it is “growing by a rate of 10 to 12 a week.”

Although the field has made significant advancements in health care providers’ ability to diagnose rare diseases, it has also highlighted what isn’t known as well, said Dr. Summar, who is also past president and a former scientific advisory board member with the National Organization for Rare Disorders (NORD).

Keeping up to date on the latest rare diseases may seem like a daunting task to the average health care professional. However, while rare diseases remain the domain of the subspecialists, the generalist “can make a tremendous impact for their patients” early in the process by having a higher suspicion for rare diseases in their practice, said Dr. Summar.

Thinking of rare diseases in categories

Many patients with undiagnosed rare diseases undergo what’s commonly referred to as a “diagnostic odyssey,” moving from one provider to another to try to find an explanation for a condition they may or may not know is rare. For some patients, this process can take many years or even decades. From the patient’s perspective, the main challenges are recognizing they have a problem that doesn’t fit a common disease model. Once they recognize they have a potential rare disease, working with a provider to find the right diagnosis among the “vast number of disease diagnoses and designations, and actually sifting through it to find the one that’s right for that patient” is the next challenge, said Dr. Summar.

However, knowledge of rare diseases among health care professionals is low, according to a 2019 paper published in the Orphanet Journal of Rare Diseases. In a survey from that paper asking general practitioners, pediatricians, specialists caring for adults, and specialists caring for children to evaluate their own knowledge of rare diseases, 42% of general practitioners said they had poor knowledge and 44% said they had a substandard understanding of rare diseases.

From a clinician’s standpoint, diagnosing rare diseases in their patients can be challenging, with the potential for overreferral or overdiagnosis. However, it is also easy to underdiagnose rare diseases by missing them, noted Dr. Summar. This issue can vary based on the experience of the provider, he said, because while general practitioners who recently began practicing may have had more exposure to rare diseases, for health care professionals who have been practicing for decades, “this is a new arrival in their field.”

During a busy day finding that extra time in an appointment to stop and question whether a patient might have a rare disease is another problem generalists face. “It is really tough for those general practitioners, because if you see 40 or 50 patients per day, how do you know which one of those [patients] were the ones that had something that wasn’t quite fitting or wasn’t quite ordinary?” he said.

When it comes to considering rare diseases in their patients, health care professionals in general practice should think in categories, rather than a particular rare disease, according to Dr. Summar. As the generalist is typically on the front lines of patient care, they don’t necessarily need to know everything about the rare disease they suspect a patient of having to help them. “You don’t need to know the specific gene and the specific mutation to make the diagnosis, or to even move the patient forward in the process,” he said.

The first steps a clinician can take include noticing when something with a patient is amiss, thinking about the disease category, and then creating a plan to move forward, such as referring the patient to a subspecialist. Learning to recognize when a cluster of symptoms doesn’t fit a pattern is important, as patients and their providers tend to gravitate toward diagnoses they are used to seeing, rather than suspecting a disease outside a usual pattern.

The framing of rare diseases as categories is a change in thinking over the last decade, said Dr. Summar. Whereas rare disease diagnoses previously focused on fitting certain criteria, the development of more refined genetic sequencing has allowed specialists to focus on categories and genes that affect rare diseases. “Getting at a diagnosis has really been turned up on its head, so that by employing both next-generation sequencing, newborn screening, and other [tools], we can actually get to diagnoses faster than we could before,” he said.

In terms of assessing for symptoms, health care professionals should be aware that “common” symptoms can be a sign of rare disease. What to look out for are the uncommon symptoms that create an “aha moment.” Having a “good filter” for sensing when something isn’t quite right with a patient is key. “It’s like any time when you’re screening things: You want high sensitivity, but you also have to have high specificity,” he said.

Another clinical pearl is that good communication between patient and provider is paramount. “We’re not always good listeners. Sometimes we hear what we expect to hear,” said Dr. Summar.

Rare disease warning signs

Within the context of rare neurological diseases, Dr. Summar noted one major category is delays in neurological development, which is typically identified in children or adolescents. As the most complex organ in the body, “the brain probably expresses more genes than any other tissue on a regular basis, both in its formation and its function,” said Dr. Summar. He said the single disease that rare disease specialists see most often is Down syndrome.

Another separate but overlapping major category is autism, identified in younger children through trouble with social interaction, lack of eye contact, and delays in speech and communication skills. A third major category is physical manifestations of neurological problems, such as in patients who have epilepsy.

A telltale sign in identifying a child with a potential rare neurological disease is when they are “not thriving in their development or not doing the things on track that you would expect, and you don’t have a really good answer for it,” said Dr. Summar. Generalists are normally on watch for developmental delays in newborns born premature or with a rough course in the nursery, but they should also be aware of delays in children born under otherwise typical circumstances. “If I have a patient who had normal pregnancy, normal labor and delivery, no real illnesses or anything like that, and yet wasn’t meeting those milestones, that’s a patient I would pay attention to,” he said.

Another clue general practitioners can use for suspecting rare diseases is when a patient is much sicker than usual during a routine illness like a cold or flu. “Those are patients we should be paying attention to because it may be there’s an underlying biochemical disorder or some disorder in how they’re responding to stress that’s just not quite right,” said Dr. Summar. How a patient responds to stressful situations can be a warning sign “because that can often unmask more severe symptoms in that rare disease and make it a little more apparent,” he said.

Learning more about rare diseases

Dr. Summar said he and his colleagues in the rare disease field have spent a lot of time working with medical schools to teach this mindset in their curricula. The concept is introduced in basic medical science courses and then reinforced in clinical rotations in the third or fourth year, he explained.

“One of the best places is during the pediatrics rotations in medical school,” he said. “Remember, kids are basically healthy. If a child has a chronic illness or a chronic disease, more often than not, it is probably a rare disease.”

For medical professionals not in pediatric practice, the concept is applied the same way for adult medicine. “You just want to make sure everyone takes a second when they have a patient and try not to assume. Don’t assume it’s exactly what it seems. Look at it carefully and make sure there’s not something else going on,” he said.

Health care professionals in general practice looking to learn more about rare diseases can increasingly find rare disease topics in their CME programs. Rare disease topics in CME programs are “one of the best places” to learn about the latest developments in the field, said Dr. Summar.

Will rare disease screening tools come to primary care?

Asking more doctors to refer out to rare disease specialists raises an issue: There simply aren’t enough rare disease specialists in the field to go around.

Dr. Summar said partnering testing – where a general practitioner contacts a specialist to begin the process of testing based on the suspected condition – is a good stopgap solution. Telemedicine, which rose in popularity during the COVID-19 pandemic, can also play an important role in connecting patients and their providers with rare disease specialists, especially for generalists in remote communities. Dr. Summar noted he continues to see approximately 30% of his patients this way today. Telemedicine appointments can take place in the patient’s home or at the provider’s office.

“It actually provides access to folks who otherwise might not be able to either take off from work for a day – particularly some of our single parent households – or have a child who just doesn’t travel well, or can’t really get there, even if it’s the patient themselves,” he explained. “We can see patients that historically would have had trouble or difficulty coming in, so for me, that’s been a good thing.”

Telemedicine also helps give access to care for more medically fragile patients, many of whom have rare diseases, he added. While some aspects of care need to occur in person, “it’s a good 80% or 90% solution for a lot of these things,” he said.

Sharing educational videos is another way for health care providers in general practice to inform patients and their families about rare diseases. Children’s National Medical Center has created a collection of these videos in a free app called GeneClips, which is available on major smartphone app stores. However, Dr. Summar emphasized that genetic counseling should still be performed by a rare disease specialist prior to testing.

“We’re still at the point where I think having genetic counseling for a family before they’re going into testing is really advisable, since a lot of the results have a probability assigned to them,” he said. “I don’t think we’re really at the level where a practitioner is going to, first of all, have the time to do those, and I don’t think there’s enough general public awareness of what these things mean.”

Although primary care providers may one day be able to perform more generalized sequencing in their own practice, that time has not yet come – but it is closer than you think. “The technology is there, and actually the cost has come down a lot,” said Dr. Summar.

One potential issue this would create is an additional discussion to manage expectations of test results with family when the results are unclear, which “actually takes more time than counseling about a yes or no, or even an outcome that is unexpected,” explained Dr. Summar.

“[W]e’re in a midlife period right now where we’re bringing forward this new technology, but we’ve got to continually prepare the field for it first,” he said. “I think in the future we’ll see that it has much greater utility in the general setting,” he said.

Jeff Craven is a freelance journalist specializing in medicine and health.

Thinking of rare diseases in categories

Rare disease warning signs

Learning more about rare diseases

Will rare disease screening tools come to primary care?

Asking more doctors to refer out to rare disease specialists raises an issue: There simply aren’t enough rare disease specialists in the field to go around.

Thinking of rare diseases in categories

Rare disease warning signs

Learning more about rare diseases

Will rare disease screening tools come to primary care?

Asking more doctors to refer out to rare disease specialists raises an issue: There simply aren’t enough rare disease specialists in the field to go around.

Birth weight below 25th percentile linked to child development problems

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Fri, 10/14/2022 - 11:45

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Peter Russell

Babies born from the 37th week of pregnancy who are mild to moderately small for gestational age (SGA) could benefit from monitoring to check for developmental problems, a study suggested.

A team of researchers at Coventry (England) University found that birth weight below the 25th percentile was associated with more developmental concerns in early childhood than a weight between the 25th and 74th percentile.

Those difficulties were apparent at percentiles higher than the conventional threshold defining SGA, they noted.

Low and high extremes of birth weight have been associated with adverse pregnancy and neonatal health outcomes, but little is known about the effects on motor skills, socialization, language, and other developmental markers for the entire range of birth weights for nonpremature babies.

Study linked health databases to child assessment results

To find out more, researchers conducted a population-based cohort study of 686,284 singleton infants born from 37 weeks of gestation, linking pregnancy and birth records from health databases covering all of Scotland to child development assessments carried out between the ages of 2 and 3.5 years.

The researchers looked for associations between birth weight and early childhood developmental concerns, taking into account confounders, such as maternal age, the mother’s medical history during pregnancy, early pregnancy body mass index, deprivation, ethnicity, alcohol use, and smoking history.

The study, published in the open access journal PLOS Medicine, found that babies born below the 25th percentile for birth weight had a higher risk of developmental concerns, compared with babies born between the 25th and 74th percentiles, with the infants who had the lowest birth weight most at risk of later developmental difficulties.

Those born between the 10th and 24th percentile had a relative risk of 1.07 (95% confidence interval, 1.03-1.12; P < .001); between the 3rd and 9th percentile, the RR was 1.18 (95% CI, 1.12-1.25, P < .001), and below the 3rd percentile the RR was 1.37 (95% CI, 1.24-1.50; P < .001).

No substantial increase in the risk of early childhood developmental concerns was identified for larger birth weight categories in the 75th-89th percentile range, the researchers reported.

Monitoring and support

The researchers concluded that having mild to moderate SGA “is an unrecognized, potentially important contributor to the prevalence of developmental concerns.”

Before this study, babies below the 10th percentile were usually considered at risk for developmental concerns. However, the investigation found a greater number of babies within the 10th-24th percentile range of birth weights with these issues, simply because there were a larger number of babies within that population.

Abiodun Adanikin, MBBS, PhD, MPH, of Coventry University’s Centre for Healthcare Research, and study first author, said: “Though it is mostly unrecognized, babies who are mild to moderately small at birth are key contributors to the burden of childhood developmental concerns. They may need closer monitoring and increased support to reduce the risk of developmental concerns.”

The study also involved colleagues from the University of Bristol (England), the University of Glasgow, the University of Cambridge (England), and Queen Mary University of London.

This work was supported by a Wellbeing of Women Research Grant. One author has received research support from Roche Diagnostics, GSK, Illumina, and Sera Prognostics (fetal growth restriction, preeclampsia and preterm birth). He has been a paid consultant to GSK (preterm birth) and is a member of a Data Monitoring Committee for GSK trials of RSV vaccination in pregnancy. He is one of three named inventors on a patent application filed by Cambridge Enterprise for novel predictive test for fetal growth disorder. He is an academic editor on PLOS Medicine’s editorial board. The authors declare no other competing interest.

A version of this article first appeared on Medscape UK.

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Babies born from the 37th week of pregnancy who are mild to moderately small for gestational age (SGA) could benefit from monitoring to check for developmental problems, a study suggested.

Study linked health databases to child assessment results

Monitoring and support

The researchers concluded that having mild to moderate SGA “is an unrecognized, potentially important contributor to the prevalence of developmental concerns.”

A version of this article first appeared on Medscape UK.

Babies born from the 37th week of pregnancy who are mild to moderately small for gestational age (SGA) could benefit from monitoring to check for developmental problems, a study suggested.

Study linked health databases to child assessment results

Monitoring and support

The researchers concluded that having mild to moderate SGA “is an unrecognized, potentially important contributor to the prevalence of developmental concerns.”

A version of this article first appeared on Medscape UK.

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Check biases when caring for children with obesity

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Eliza Partika

Counting calories should not be the focus of weight-loss strategies for children with obesity, according to an expert who said pediatricians need to change the way they discuss weight with their patients.

During a plenary session of the American Academy of Pediatrics National Conference, Joseph A. Skelton, MD, professor of pediatrics at Wake Forest University School of Medicine, Winston-Salem, N.C., said pediatricians should recognize the behavioral, physical, environmental, and genetic factors that contribute to obesity. For instance, food deserts are on the rise, and they undermine the ability of parents to feed their children healthy meals. In addition, more children are less physically active.

“Obesity is a lot more complex than calories in, calories out,” Dr. Skelton said. “We choose to treat issues of obesity as personal responsibility – ‘you did this to yourself’ – but when you look at how we move around and live our lives, our food systems, our policies, the social and environmental changes have caused shifts in our behavior.”

According to Dr. Skelton, bias against children with obesity can harm their self-image and weaken their motivations for losing weight. In addition, doctors may change how they deliver care on the basis of stereotypes regarding obese children. These stereotypes are often reinforced in media portrayals, Dr. Skelton said.

“When children or when adults who have excess weight or obesity are portrayed, they are portrayed typically in a negative fashion,” Dr. Skelton said. “There’s increasing evidence that weight bias and weight discrimination are increasing the morbidity we see in patients who develop obesity.”

For many children with obesity, visits to the pediatrician often center on weight, regardless of the reason for the appointment. Weight stigma and bias on the part of health care providers can increase stress, as well as adverse health outcomes in children, according to a 2019 study (Curr Opin Endocrinol Diabetes Obes. 2019 Feb 1. doi: 10.1097/MED.0000000000000453). Dr. Skelton recommended that pediatricians listen to their patients’ concerns and make a personalized care plan.

Dr. Skelton said doctors can pull from projects such as Health at Every Size, which offers templates for personalized health plans for children with obesity. It has a heavy focus on a weight-neutral approach to pediatric health.

“There are various ways to manage weight in a healthy and safe way,” Dr. Skelton said.

Evidence-based methods of treating obesity include focusing on health and healthy behaviors rather than weight and using the body mass index as a screening tool for further conversations about overall health, rather than as an indicator of health based on weight.

Dr. Skelton also encouraged pediatricians to be on the alert for indicators of disordered eating, which can include dieting, teasing, or talking excessively about weight at home and can involve reading misinformation about dieting online.

“Your job is to educate people on the dangers of following unscientific information online,” Dr. Skelton said. “We can address issues of weight health in a way that is patient centered and is very safe, without unintended consequences.” Brooke Sweeney, MD, professor of internal medicine and pediatrics at University of Missouri–Kansas City, said problems with weight bias in society and in clinical practice can lead to false assumptions about people who have obesity.

“It’s normal to gain adipose, or fat tissue, at different times in life, during puberty or pregnancy, and some people normally gain more weight than others,” Dr. Sweeney said.

The body will try to maintain a weight set point. That set point is influenced by many factors, such as genetics, environment, and lifestyle.

“When you lose weight, your body tries to get you back to the set point, decreasing energy expenditure and increasing hunger and reward pathways,” she said. “We have gained so much knowledge through research to better understand the pathophysiology of obesity, and we are making good progress on improving advanced treatments for increased weight in children.”

Dr. Skelton reports no relevant financial relationships.

A version of this article first appeared on Medscape.com.

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Pediatricians urged to check for vision problems after concussion

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Mary Chris Jaklevic

Pediatricians should consider screening children suspected of having a concussion for resulting vision problems that are often overlooked, according to the American Academy of Pediatrics.

Christina Master, MD, a pediatrician and sports medicine specialist at the Children’s Hospital of Philadelphia, said many doctors don’t think of vision problems when examining children who’ve experienced a head injury. But the issues are common and can significantly affect a child’s performance in school and sports, and disrupt daily life.

Dr. Master led a team of sports medicine and vision specialists who wrote an AAP policy statement on vision and concussion. She summarized the new recommendations during a plenary session Oct. 9 at the American Academy of Pediatrics National Conference.

Dr. Master told this news organization that the vast majority of the estimated 1.4 million U.S. children and adolescents who have concussions annually are treated in pediatricians’ offices.

Up to 40% of young patients experience symptoms such as blurred vision, light sensitivity, and double vision following a concussion, the panel said. In addition, children with vision problems are more likely to have prolonged recoveries and delays in returning to school than children who have concussions but don’t have similar eyesight issues.

Concussions affect neurologic pathways of the visual system and disturb basic functions such as the ability of the eyes to change focus from a distant object to a near one.

Dr. Master said most pediatricians do not routinely check for vision problems following a concussion, and children themselves may not recognize that they have vision deficits “unless you ask them very specifically.”

In addition to asking children about their vision, the policy statement recommends pediatricians conduct a thorough exam to assess ocular alignment, the ability to track a moving object, and the ability to maintain focus on an image while moving.

Dr. Master said that an assessment of vision and balance, which is described in an accompanying clinical report, lasts about 5 minutes and is easy for pediatricians to learn.

Managing vision problems

Pediatricians can guide parents in talking to their child’s school about accommodations such as extra time on classroom tasks, creating materials with enlarged fonts, and using preprinted or audio notes, the statement said.

At school, vision deficits can interfere with reading by causing children to skip words, lose their place, become fatigued, or lose interest, according to the statement.

Children can also take breaks from visual stressors such as bright lights and screens, and use prescription glasses temporarily to correct blurred vision, the panel noted.

Although most children will recover from a concussion on their own within 4 weeks, up to one-third will have persistent symptoms and may benefit from seeing a specialist who can provide treatment such as rehabilitative exercises. While evidence suggests that referring some children to specialty care within a week of a concussion improves outcomes, the signs of who would benefit are not always clear, according to the panel.

Specialties such as sports medicine, neurology, physiatry, otorhinolaryngology, and occupational therapy may provide care for prolonged symptoms, Dr. Master said.

The panel noted that more study is needed on treatment options such as rehabilitation exercises, which have been shown to help with balance and dizziness.

Dr. Master said the panel did not recommend that pediatricians provide a home exercise program to treat concussion, as she does in her practice, explaining that “it’s not clear that it’s necessary for all kids.”

One author of the policy statement, Ankoor Shah, MD, PhD, reported an intellectual property relationship with Rebion involving a patent application for a pediatric vision screener. Others, including Dr. Master, reported no relevant financial relationships.

A version of this article first appeared on Medscape.com.

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Pediatricians should consider screening children suspected of having a concussion for resulting vision problems that are often overlooked, according to the American Academy of Pediatrics.

Managing vision problems

A version of this article first appeared on Medscape.com.

Pediatricians should consider screening children suspected of having a concussion for resulting vision problems that are often overlooked, according to the American Academy of Pediatrics.

Managing vision problems

A version of this article first appeared on Medscape.com.

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With sleuth work, pediatricians can identify genetic disorders

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Jennifer Kalish, MD, PhD, fields as many as 10 inquiries a month from pediatricians who spot an unusual feature during a clinical exam, and wonder if they should refer the family to a geneticist.

“There are hundreds of rare disorders, and for a pediatrician, they can be hard to recognize,” Dr. Kalish said. “That’s why we’re here as geneticists – to partner so that we can help.”

Pediatricians play a key role in spotting signs of rare genetic diseases, but may need guidance for recognizing the more subtle presentations of a disorder, according to Dr. Kalish, a geneticist and director of the Beckwith-Wiedemann Syndrome Clinic at Children’s Hospital of Philadelphia, who spoke at the American Academy of Pediatrics National Conference.

Spectrums of disease

Pediatricians may struggle with deciding whether to make a referral, in part because genetic syndromes “do not always look like the textbook,” she said.

With many conditions, “we’re starting to understand that there’s really a spectrum of how affected versus less affected one can be,” by genetic and epigenetic changes, which have led to recognition that many cases are more subtle and harder to diagnose, she said.

Beckwith-Wiedemann syndrome is a prime example. The overgrowth disorder affects an estimated 1 in 10,340 infants, and is associated with a heightened risk of Wilms tumors, a form of kidney cancer, and hepatoblastomas. Children diagnosed with these conditions typically undergo frequent screenings to detect tumors to jumpstart treatment.

Some researchers believe Beckwith-Wiedemann syndrome is underdiagnosed because it can present in many different ways because of variations in the distributions of affected cells in the body, known as mosaicism.

To address the complexity, Dr. Kalish guided development of a scoring system for determining whether molecular testing is warranted. Primary features such as an enlarged tongue and lateralized overgrowth carry more points, whereas suggestive features like ear creases or large birth weight carry fewer points.

Diagnostic advances have occurred for other syndromes, as well. For example, researchers have created a scoring system for Russell-Silver syndrome, a less common disorder characterized by slow growth before and after birth, in which mosaicism is also present.

Early diagnosis and intervention of Russell-Silver syndrome can ensure that patients grow to their maximum potential and address problems such as feeding issues.

Spotting a “compilation of features”

Although tools are available, Dr. Kalish said pediatricians don’t need to make a diagnosis, and instead can refer patients to a geneticist after recognizing clinical features that hint at a genetic etiology.

For pediatricians, the process of deciding whether to refer a patient to a geneticist may entail ruling out nongenetic causes, considering patient and family history, and ultimately deciding whether there is a “compilation of features” that falls outside the norm, she said. Unfortunately, she added, there’s “not a simple list I could just hand out saying, ‘If you see these things, call me.’ ”

Dr. Kalish said pediatricians should be aware that two children with similar features can have different syndromes. She presented case studies of two infants, who both had enlarged tongues and older mothers.

One child had hallmarks that pointed to Beckwith-Wiedemann syndrome: conception with in vitro fertilization, length in the 98th percentile, a long umbilical cord, nevus simplex birthmarks, and labial and leg asymmetry.

The other baby had features aligned with Down syndrome: a heart murmur, upward slanting eyes, and a single crease on the palm.

In some cases, isolated features such as the shape, slant, or spacing of eyes, or the presence of creases on the ears, may simply be familial or inherited traits, Dr. Kalish said.

She noted that “there’s been a lot of work in genetics in the past few years to show what syndromes look like” in diverse populations. The American Journal of Medical Genetics Part A has published a series of reports on the topic.

Dr. Kalish reported no relevant financial relationships.

A version of this article first appeared on Medscape.com.

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Jennifer Kalish, MD, PhD, fields as many as 10 inquiries a month from pediatricians who spot an unusual feature during a clinical exam, and wonder if they should refer the family to a geneticist.

Spectrums of disease

Pediatricians may struggle with deciding whether to make a referral, in part because genetic syndromes “do not always look like the textbook,” she said.

Spotting a “compilation of features”

A version of this article first appeared on Medscape.com.

Jennifer Kalish, MD, PhD, fields as many as 10 inquiries a month from pediatricians who spot an unusual feature during a clinical exam, and wonder if they should refer the family to a geneticist.

Spectrums of disease

Pediatricians may struggle with deciding whether to make a referral, in part because genetic syndromes “do not always look like the textbook,” she said.

Spotting a “compilation of features”

A version of this article first appeared on Medscape.com.

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Epidemiology and description

Screening and testing

Diagnosis: Signs and symptoms

Treatment: Present and future

Conclusion

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Epidemiology and description

Screening and testing

Diagnosis: Signs and symptoms

Treatment: Present and future

Conclusion

References

Epidemiology and description

Screening and testing

Diagnosis: Signs and symptoms

Treatment: Present and future

Conclusion

References

Amyotrophic lateral sclerosis

Treatment of ALS

Gene-based therapy for ALS

Spinal muscular atrophy

Gene-based therapy for SMA

Duchenne muscular dystrophy

Therapy for DMD

Gene-based therapy for DMD

Challenges ahead, but advancements realized

References

Amyotrophic lateral sclerosis

Treatment of ALS

Gene-based therapy for ALS

Spinal muscular atrophy

Gene-based therapy for SMA

Duchenne muscular dystrophy

Therapy for DMD

Gene-based therapy for DMD

Challenges ahead, but advancements realized

References

Amyotrophic lateral sclerosis

Treatment of ALS

Gene-based therapy for ALS

Spinal muscular atrophy

Gene-based therapy for SMA

Duchenne muscular dystrophy

Therapy for DMD

Gene-based therapy for DMD

Challenges ahead, but advancements realized

References

Advances in early diagnosis

Who to treat, when, and with which treatment

Research advances in 2021

What’s needed next

Two deaths from liver failure linked to spinal muscular atrophy drug

Rare genetic disorder

References

Advances in early diagnosis

Who to treat, when, and with which treatment

Research advances in 2021

What’s needed next

Two deaths from liver failure linked to spinal muscular atrophy drug

Rare genetic disorder

References

Advances in early diagnosis

Who to treat, when, and with which treatment

Research advances in 2021

What’s needed next

Two deaths from liver failure linked to spinal muscular atrophy drug

Rare genetic disorder

References

Underlying molecular cause

Presentation

A life-changing diagnosis

Current treatments

Clinical trials

Is the future about gene therapy?

Conclusion

References

Underlying molecular cause

Presentation