Biogen secures FDA breakthrough status for once-yearly spinal muscular atrophy drug Salanersen

USA—Biogen has received Breakthrough Therapy Designation from the U.S. Food and Drug Administration for salanersen (BIIB115), an investigational treatment for Spinal Muscular Atrophy (SMA).

The designation reflects early clinical evidence suggesting that the therapy could deliver meaningful improvements over currently available SMA treatments.

It also strengthens the drug’s development pathway as the company advances its neurology pipeline.

Promising early clinical findings

The regulatory decision follows results from a Phase Ib study presented at the 2026 Muscular Dystrophy Association Clinical and Scientific Conference and the 2026 International Scientific Congress on SMA Europe.

The study enrolled children with SMA, including those who had previously shown suboptimal responses to gene therapy.

In this trial, once-yearly administration of salanersen demonstrated measurable improvements in motor function, alongside a slowdown in neurodegeneration, as indicated by reduced neurofilament light chain levels.

Researchers reported that all participants showed improvement in at least one clinical endpoint, while 12 of 24 achieved new motor milestones defined by the World Health Organization.

Most adverse events remained mild to moderate, supporting an overall tolerable safety profile.

Phase III development expands globally

Biogen has now advanced Salanersen into a broad Phase III program comprising three global studies.

The STELLAR-I trial is currently recruiting infants under six weeks old, including both presymptomatic and treatment-naïve patients with genetically confirmed SMA.

Meanwhile, the SOLAR study is enrolling adolescents and adults aged 15 to 60 years, covering both untreated individuals and those previously exposed to risdiplam.

In addition, STELLAR-II is scheduled to begin recruitment in June 2026.

This study will evaluate outcomes in infants who previously received onasemnogene abeparvovec-xioi gene therapy before six weeks of age, offering insight into sequencing and combination strategies in early intervention.

Mechanism and therapeutic potential

Salanersen is an intrathecally administered antisense oligonucleotide designed to modify the splicing of SMN2 pre-mRNA, thereby increasing the production of survival motor neuron protein.

Its novel chemistry supports once-yearly dosing, which could significantly reduce treatment burden for patients and caregivers if approved.

Expert perspective and pipeline context

Biogen’s rare neurology development head, Stephanie Fradette, said the designation highlights the FDA’s recognition of the therapy’s potential to outperform existing options.

She further noted that the milestone marks an important step for the company’s SMA portfolio as it transitions into late-stage clinical development.

Earlier in the year, Biogen also secured Breakthrough Therapy Designation for litifilimab (BIIB059) in cutaneous lupus erythematosus, reinforcing its continued focus on advancing therapies for complex neurological and autoimmune conditions.