FDA Approves ISEMBYLD for SMA Patients 2 and Older Receiving SMN2 Therapy

Key Facts

The U.S. Food and Drug Administration, or FDA, approved Scholar Rock’s ISEMBYLD (apitegromab-mstn) on September 11, 2026, for adults and children aged 2 years and older with spinal muscular atrophy, or SMA, who are currently receiving an SMN2-targeted treatment. The decision adds the first therapy designed to target the muscular component of the disease directly to background SMN2 treatment.

ISEMBYLD is a fully human IgG4 monoclonal antibody that binds inactive forms of myostatin and prevents their activation. Myostatin limits muscle growth, so the drug is designed to target muscle while background SMN2 therapies address the pathway associated with motor-neuron loss.

Approval was based on the randomized, double-blind Phase 3 SAPPHIRE study. The recommended 10 mg/kg dose of ISEMBYLD with SMN2 therapy produced a 2.2-point difference on the HFMSE motor-function scale after 1 year versus background treatment with placebo in the main efficacy population aged 2 to 12 years, comprising 103 patients, with nominal p=0.0121.

A gain of at least 3 HFMSE points was recorded in 34.2% of ISEMBYLD recipients, compared with 13.5% on placebo, for an odds ratio of 3.8 and nominal p=0.0125. On safety, fractures occurred in 9% of patients receiving the 10 mg/kg dose versus 2% in the placebo group.

Scholar Rock said the U.S. commercial launch was underway and ISEMBYLD would be available to ship within days. It also said it was engaging commercial and government payers on coverage, shifting the focus for SRRK from the FDA decision to launch execution and patient access.

Ahead of the announcement, Scholar Rock shares, traded as SRRK, closed at $55.67 on September 10, 2026, after ranging from $53.86 to $56.71 during the session. Those figures provide a pre-approval reference and do not by themselves establish the market reaction or a technical support level.

Outside the United States, the regulatory process remains separate. The European Medicines Agency said the ISEMBYLD application was withdrawn on August 13, 2026, after timely confirmation of the manufacturing site’s compliance with European good manufacturing practice was not provided; Scholar Rock said it planned to resubmit using an alternate fill-finish facility.