FDA Approves the First Spinal Muscular Atrophy Drug That Targets Muscle Loss

The U.S. Food and Drug Administration approved Isembyld, an infused drug for spinal muscular atrophy, on Sept. 11, 2026, for adults and children aged 2 and older who are already taking an existing treatment. The agency calls it the first therapy approved for the disease that targets muscle loss directly.

Spinal muscular atrophy is inherited, gets worse over time, and weakens and wastes muscle. It comes from a faulty gene that fails to make a protein motor neurons need to survive, and the FDA says the disease is rare and among the leading genetic causes of infant death. Every treatment approved for it so far works on a backup gene to keep those nerve cells alive; patients with more advanced disease still lose the ability to walk or move on their own. Isembyld is given alongside those treatments, not in place of them.

The approval rests on a 52-week trial that enrolled 188 people aged 2 to 21 who could not walk or move independently and were already on an existing treatment. Participants were assigned at random to one of two doses of Isembyld or to a placebo, given by drip every four weeks. In the main analysis, which covered 156 children, those on the lower dose were more than twice as likely as those on placebo to show a meaningful gain in motor ability, the agency reported. Motor function improved over the year in the treated group and declined in the placebo group.

The FDA also recorded an increased risk of fractures, including serious ones, in patients given Isembyld, and says it may cause fetal harm and may affect reproductive function. The most common side effects were upper respiratory infections, vomiting, cough, other viral infections, headache, stomach and bowel infection, and sore throat.

Isembyld carried Fast Track, Orphan Drug, and Rare Pediatric Disease designations, which speed FDA review of treatments for rare and childhood conditions. The approval was granted to Scholar Rock, Inc.