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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. 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.
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. 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.
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. 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.
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