FDA Approves Scholar Rock's Isembyld for Spinal Muscular Atrophy

Scholar Rock has received its first regulatory approval, with the U.S. Food and Drug Administration clearing its injectable therapy Isembyld for a rare genetic condition that causes progressive muscle weakness.

The treatment is indicated for adults and children with spinal muscular atrophy who have already been treated with existing therapies for the condition. It is the first muscle-targeted therapy designed to improve motor function in this group.

Spinal muscular atrophy damages motor neurons, leading to worsening weakness and difficulties with movement, breathing and swallowing. The Muscular Dystrophy Association estimates that roughly 10,000 children and adults in the United States live with the condition.

Isembyld, chemically known as apitegromab, works by selectively blocking the activation of myostatin, a protein that restricts muscle growth, with the goal of building muscle mass and strength. The approval rests on late-stage data showing that the therapy significantly improved motor function compared with placebo.

The drug enters a market that includes Biogen's Spinraza, Novartis' gene therapy Zolgensma and Roche's oral Evrysdi. Scholar Rock has said it would manufacture Isembyld at a U.S.-based facility. The company did not immediately respond to a request for comment on pricing and availability, and its shares were halted in aftermarket trading.

Analysts see room for growth. Cantor said the approval positions Scholar Rock as one of biotech's strongest long-term growth stories, citing potential geographic, indication and product-line expansion. BMO Capital Markets analyst Evan Seigerman forecasts 2035 adjusted worldwide peak sales of $2.1 billion.

Beyond SMA, Scholar Rock is testing the drug to preserve muscle in obesity, where it would compete with more than a dozen companies developing treatments aimed at limiting muscle loss during weight loss.