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Spinal Muscular Atrophy

Recent research efforts aimed at curing Spinal Muscular Atrophy.

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Spinal Muscular Atrophy

Overview

Spinal muscular atrophy (SMA) is an inherited neuromuscular disease in which too little survival motor neuron (SMN) protein causes the loss of motor neurons—the nerve cells that control voluntary muscles. Most cases result from having nonworking copies of the SMN1 gene; the related SMN2 gene makes some SMN protein and partly modifies severity. SMA ranges from severe infantile-onset disease, with profound weakness and risks to breathing and feeding, to later-onset forms in children and adults that mainly affect mobility and independence. Disease-modifying therapies for SMA (pubmed.ncbi.nlm.nih.gov)

Current care combines prompt SMN-directed treatment with multidisciplinary respiratory, nutritional, orthopedic, rehabilitation, and psychosocial support. In the United States, the three established disease-modifying options are intrathecal nusinersen, oral risdiplam, and one-time intravenous onasemnogene abeparvovec; all increase functional SMN through different mechanisms, but none has been proven to reverse all established nerve and muscle damage. Treatment-considerations consensus Updated long-term evidence review (pmc.ncbi.nlm.nih.gov)

Scope of Recent Research (2020–present)

Research since 2020 has been exceptionally active, shifting from demonstrating that raising SMN can alter SMA’s course to tackling residual weakness, treating people already living with longstanding disease, optimizing one-time gene delivery, and developing permanent correction of SMN2. The field is close to preventing severe disease when treatment starts before symptoms, but it is not yet close to a universal biological cure because lost motor neurons are difficult to replace, long-term durability remains uncertain, and curative gene-editing approaches are still preclinical. Presymptomatic-treatment systematic review Emerging targeted-therapy review (pubmed.ncbi.nlm.nih.gov)

Major Breakthroughs and Emerging Therapies

The most consequential advance remains earlier SMN restoration. Nusinersen and risdiplam alter SMN2 RNA splicing so that more full-length SMN protein is made, while onasemnogene abeparvovec uses an adeno-associated virus 9 (AAV9) vector to deliver a functional SMN1 gene. Studies of presymptomatic treatment consistently show substantially better developmental outcomes when babies are identified through newborn screening and treated before motor-neuron loss becomes clinically apparent. Disease-modifying therapies for SMA Presymptomatic-treatment systematic review (pubmed.ncbi.nlm.nih.gov)

A major recent gene-therapy development is intrathecal onasemnogene abeparvovec (OAV101 IT), designed to place AAV9-delivered SMN1 closer to spinal motor neurons and extend gene replacement to older children with later-onset SMA. In the randomized Phase 3 STEER trial of treatment-naive participants aged 2 to under 18 years with nonambulatory type 2 SMA, a single intrathecal dose improved motor function relative to sham treatment over 52 weeks. STEER Phase 3 trial (nature.com)

Researchers are also testing combination strategies that address consequences of SMA not fully corrected by SMN restoration. Apitegromab is an antibody that inhibits activation of myostatin, a protein that restrains muscle growth; it is intended to improve muscle strength and function when added to nusinersen or risdiplam rather than to correct the underlying genetic defect. The Phase 3 SAPPHIRE study enrolled nonambulatory people with type 2 or type 3 SMA receiving background SMN therapy and compared monthly intravenous apitegromab with placebo. SAPPHIRE Phase 3 protocol (cdn.clinicaltrials.gov)

The most genuinely “curative” experimental direction is genome editing. Several groups have used CRISPR-derived adenine base editors to convert the critical SMN2 exon-7 sequence toward the SMN1-like version, thereby permanently increasing correct exon inclusion and SMN production. In an SMA mouse model, AAV9-delivered base editing improved motor performance and lifespan; a separate study optimized high-fidelity editors in patient fibroblasts and mice. These are important proof-of-concept results, but they are not human treatments and still require convincing evidence of safe delivery, durability, and absence of harmful off-target edits. Base-editing rescue in cells and mice Optimized SMN2 base editors (pubmed.ncbi.nlm.nih.gov)

Clinical Trials and Experimental Approaches

Notable recent clinical programs include Novartis’s Phase 3 STEER study of one-time intrathecal OAV101 in treatment-naive, nonambulatory children with type 2 SMA, which reported a statistically significant motor-function benefit over sham control. Novartis also studied intrathecal OAV101 in treatment-experienced patients through the Phase 3b STRENGTH program, testing whether a one-time spinal gene-transfer approach can add benefit after nusinersen or risdiplam. STEER Phase 3 trial STRENGTH trial protocol (nature.com)

Biogen and Ionis have advanced salanersen (BIIB115/ION306), a next-generation intrathecal antisense oligonucleotide designed to increase SMN production with less frequent dosing than nusinersen. In June 2025, the companies reported interim Phase 1 findings in children previously treated with onasemnogene abeparvovec and announced plans for registrational studies; these results were sponsor-reported and require full peer-reviewed publication. In parallel, Scholar Rock’s Phase 3 SAPPHIRE trial evaluates apitegromab as an add-on muscle-directed therapy, not as a cure. Salanersen Phase 1 update SAPPHIRE Phase 3 protocol (ir.ionispharma.com)

Methodologies and Scientific Approaches

SMA cure research relies on complementary systems: genetically engineered mouse models for survival and motor testing; patient-derived fibroblasts and induced pluripotent stem cells (iPSCs) for testing human genetic backgrounds; and spinal-cord organoids, which model early motor-neuron development in three dimensions. Recent isogenic iPSC-organoid work found developmental abnormalities before overt motor-neuron loss, supporting the idea that a complete cure may need to address early developmental as well as degenerative effects of low SMN. SMA spinal-cord organoid study (pubmed.ncbi.nlm.nih.gov)

Delivery technology is central. AAV9 is used for SMN1 gene replacement and experimental base-editor delivery, while antisense oligonucleotides are administered into cerebrospinal fluid to modify SMN2 splicing. Researchers also use motor scales, electrophysiology, imaging, and blood or cerebrospinal-fluid biomarkers such as neurofilament proteins to measure nerve injury and treatment response; however, biomarker performance differs by age and disease stage. SMA biomarker working-group report Neurofilament study in adults (pubmed.ncbi.nlm.nih.gov)

Leading Institutions and Funding

The field is driven by multicenter academic neuromuscular programs, including Massachusetts General Hospital and Harvard Medical School, the University of Ottawa, Nationwide Children’s Hospital, Columbia University, St. Jude Children’s Research Hospital, and specialist SMA centers internationally. Industry sponsors are particularly important for late-stage development: Novartis for onasemnogene abeparvovec programs, Biogen and Ionis for salanersen, Roche/Genentech for risdiplam, and Scholar Rock for apitegromab. Optimized SMN2 base editors SMA treatment-considerations consensus SMA drug pipeline (pubmed.ncbi.nlm.nih.gov)

Patient-led funding remains influential. Cure SMA reported more than $85 million invested in basic research grants and drug-discovery programs by 2024, including six new basic-research grants totaling $750,000 that year and a further planned $750,000 funding round. Cure SMA 2024 research funding (curesma.org)

Strengths, Limitations, and Challenges

The strongest evidence is that rapid SMN restoration—especially before symptoms—can dramatically alter outcomes. Nevertheless, the approved therapies are disease-modifying rather than uniformly restorative: systematic evidence finds motor improvements but less consistent improvement in respiratory and nutritional outcomes, while important questions remain about lifelong durability, treatment sequencing, switching, and combination therapy. Updated long-term evidence review Presymptomatic-treatment systematic review (pubmed.ncbi.nlm.nih.gov)

Safety and access remain substantial constraints. Intrathecal nusinersen requires repeated lumbar punctures; risdiplam requires chronic daily dosing; and intravenous onasemnogene abeparvovec has a boxed warning for serious liver injury and requires corticosteroids and laboratory monitoring for liver toxicity, low platelets, and thrombotic microangiopathy. AAV-based approaches also face immune barriers and currently lack an established redosing strategy. SPINRAZA prescribing information EVRYSDI prescribing information ZOLGENSMA prescribing information (dailymed.nlm.nih.gov)

Outlook and Future Directions

As of September 29, 2026, SMA is increasingly preventable as a devastating early-life disease when newborn screening enables immediate treatment, but no therapy can yet be described honestly as a complete cure for all people with SMA. The milestones to watch are long-term outcomes after presymptomatic treatment, regulatory and peer-reviewed results for intrathecal OAV101 and salanersen, whether muscle-directed add-ons yield meaningful functional gains, and—furthest from the clinic—successful safety and delivery studies that move permanent SMN2 base editing from mice into human trials. Presymptomatic-treatment systematic review STEER Phase 3 trial Base-editing rescue in cells and mice (pubmed.ncbi.nlm.nih.gov)

References

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