FDA approves the first muscle-targeted therapy for SMA

The US Food and Drug Administration approved ISEMBYLD (apitegromab-mstn) on 11 September 2026, Scholar Rock’s antibody for spinal muscular atrophy. It is cleared for adults and children aged two and over who are already receiving a therapy directed at the SMN protein, and it is taken alongside that therapy rather than in place of it.

Every SMA drug approved before this one works on the motor neuron: it raises SMN protein so that the nerve cells controlling muscle survive. ISEMBYLD acts on the muscle itself, inhibiting latent myostatin, a signal that restrains muscle growth. That makes it the first approved SMA treatment aimed at the muscle loss rather than at its neurological cause.

Approval rests on SAPPHIRE, a randomised double-blind Phase 3 trial in 188 patients aged 2 to 21 with 5q SMA across nine countries. Participants received 20 mg/kg, 10 mg/kg — the dose carried into the label — or placebo by infusion every four weeks for about a year. The 10 mg/kg arm gained 2.2 points over placebo on the Hammersmith Functional Motor Scale Expanded, a measure of what a patient can physically do: sitting, rolling, standing, lifting.

The scale matters more than the number. It counts movements, not biomarkers.