Biogen has received a significant regulatory boost for its investigational spinal muscular atrophy (SMA) therapy salanersen after the U.S. Food and Drug Administration (FDA) granted the treatment Breakthrough Therapy Designation. The designation is intended to accelerate the development and review of therapies that may offer substantial improvements over existing treatment options for serious or life-threatening diseases.
The FDA’s decision is based on preliminary clinical evidence from a Phase 1b study evaluating salanersen in children with SMA who had previously received gene therapy but experienced suboptimal responses. According to Biogen, the investigational therapy demonstrated clinically meaningful improvements in motor function and showed signs of slowing neurodegeneration, supporting its potential as a next-generation treatment for the rare neuromuscular disorder.
Salanersen is a novel antisense oligonucleotide (ASO) designed to treat SMA with the possibility of once-yearly dosing, a feature that could differentiate it from currently available therapies requiring more frequent administration. The company believes the treatment may offer both convenience and improved outcomes for patients living with the disease.
Spinal muscular atrophy is a rare genetic condition characterized by the loss of motor neurons, leading to progressive muscle weakness and impaired movement. Although advances in gene therapy and RNA-based treatments have transformed care for many patients, experts and patient advocates say significant unmet needs remain, particularly among individuals who do not achieve optimal results from currently available therapies.
Data supporting the designation were recently presented at the 2026 Muscular Dystrophy Association Clinical & Scientific Conference and the 5th International Scientific Congress on SMA. Researchers reported that children who had previously received gene therapy experienced improvements in key motor milestones after treatment with salanersen. Some patients gained important functional abilities, including sitting and walking, outcomes that are especially meaningful in a disease that can severely limit mobility and independence.
Investigators also observed reduced levels of neurofilament, a biomarker associated with nerve cell damage, suggesting that salanersen may help slow ongoing neurodegeneration. The therapy was generally well tolerated in the study, with no major safety concerns reported.
Diana Castro, M.D., of the Neurology Rare Disease Center in Texas, described the findings as encouraging and noted that the observed gains in motor function exceeded expectations in some previously treated patients. She emphasized the importance of continuing to explore therapies that can address remaining treatment gaps in SMA.
Patient advocacy organizations also welcomed the FDA’s decision. Kenneth Hobby, President of Cure SMA, said the designation highlights the ongoing need for innovative therapies and reflects growing recognition that many individuals with SMA could still benefit from additional treatment options.
Biogen is now advancing a broad global Phase 3 development program for salanersen. The program includes STELLAR-1, which is currently recruiting presymptomatic infants diagnosed with SMA; SOLAR, which is enrolling adolescents and adults aged 15 to 60 years; and STELLAR-2, a randomized, sham-controlled study expected to begin recruitment in June 2026. The latter trial will evaluate salanersen in infants who previously received gene therapy early in life.
The Breakthrough Therapy Designation represents an important milestone for Biogen’s rare neurology portfolio and could help expedite the development of what may become a new treatment option in the evolving SMA landscape.