This advance recognises preliminary data indicating that salanersen may show substantial improvement over existing therapies for SMA.
The FDA’s decision follows data from a Phase Ib study on salanersen, presented at the 2026 Muscular Dystrophy Association Clinical and Scientific Conference and the fifth International Scientific Congress on SMA Europe 2026.
The study included children with SMA who had previously responded suboptimally to gene therapy.
Once-yearly administration of salanersen led to marked improvements in motor function and a slowdown in neurodegeneration, measured by reduced neurofilament levels. The treatment was generally well-tolerated.
Biogen rare neurology development unit head Stephanie Fradette said: “This designation reflects the FDA’s determination that salanersen has the potential to demonstrate substantial improvement over available therapies.
“This is a significant milestone for our SMA portfolio as we advance the Phase III studies designed to establish the role of salanersen in the future SMA treatment landscape.”
The salanersen Phase III programme comprises three global studies. The STELLAR-I study, currently recruiting, focuses on infants under six weeks old, both treatment-naïve and clinically presymptomatic, with a genetic diagnosis of SMA.
The SOLAR study, also recruiting, will assess teens and adults (aged 15-60 years) with SMA, including those who are either treatment-naïve or have been treated with risdiplam.
STELLAR-II, planned to start recruiting in June 2026, will compare outcomes after onasemnogene abeparvovec-xioi treatment in infants previously treated with gene therapy before six weeks of age.
Salanersen is an intrathecally administered antisense oligonucleotide designed to correct the splicing of survival motor neuron 2 (SMN2) pre-messenger ribonucleic acid (mRNA), increasing production of SMN protein. It uses new chemistry to enable once-yearly dosing.
In a Phase Ib study involving 24 participants aged 0.5–12 years, a meaningful reduction in neurofilament light chain was observed at six months and sustained throughout the follow-up.
All participants had improvements in one or more endpoints, with 12 of 24 achieving at least one new World Health Organization (WHO) motor milestone. Most adverse events were mild to moderate.
SMA is a rare, genetic neuromuscular disease leading to progressive muscle weakness due to the loss of motor neurons.
Earlier this year, the FDA granted breakthrough therapy designation to Biogen’s litifilimab (BIIB059) for cutaneous lupus erythematosus, a chronic autoimmune skin condition.