Rare Daily Staff
The U.S. Food and Drug Administration has granted Breakthrough Therapy designation to Biogen’s experimental drug salanersen for the rare neuromuscular condition spinal muscular atrophy.
The designation is intended to speed the development and review of drugs that show early signs of substantial improvement over existing treatments, and it underscores that, despite recent advances, many patients with SMA still have unmet medical needs.
The FDA’s decision was based on early-stage clinical data in children who had previously received gene therapy but continued to experience disease symptoms. In that small study, some patients showed slowed nerve damage and meaningful gains in motor function after starting salanersen, with some children achieving new milestones such as sitting or walking.
Spinal muscular atrophy is a leading genetic cause of death in infants. The disease progressively damages motor neurons, leading to muscle weakness that can affect basic functions such as breathing, swallowing, and movement.
Salanersen is part of a newer generation of therapies designed to boost levels of a critical protein called SMN, which people with SMA lack. Unlike some current treatments that may require frequent dosing, salanersen is being developed as a once-yearly injection into the spinal fluid, a schedule that could ease the burden on patients and families.
Biogen is now advancing salanersen into late-stage testing. Three global phase 3 trials are underway or about to begin, including studies in newborns diagnosed before symptoms appear, as well as in teenagers and adults. Another trial will evaluate the drug in infants who have already received gene therapy.
In the early study, all 24 participants showed improvement on at least one measure of motor function, and half achieved new developmental milestones. The drug was generally well tolerated, with most side effects described as mild to moderate, such as fever or respiratory infections.
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