Scholar Rock Launches ISEMBYLD (Apitegromab-Mstn) as First Muscle-Targeted Therapy for Spinal Muscular Atrophy Following September 11 FDA Approval for Ages 2 and Older on SMN2-Targeted Background
Scholar Rock Inc. (NASDAQ: SRRK) announced Monday September 14, 2026 the commercial launch of ISEMBYLD (apitegromab-mstn) following FDA approval on September 11, 2026 for the treatment of spinal muscular atrophy (SMA) in adults and children two years of age and older who are receiving a survival motor neuron 2 (SMN2)-targeted background therapy (Biogen's Spinraza / nusinersen, Novartis's Zolgensma / onasemnogene abeparvovec, or Roche's Evrysdi / risdiplam). ISEMBYLD is a fully human IgG4 monoclonal antibody that binds to promyostatin and latent myostatin (a peptide that limits muscle growth) and inhibits the activation of myostatin, blocking myostatin signaling to preserve and build muscle. The FDA action makes ISEMBYLD the first-and-only muscle-targeted SMA therapy — an addition to rather than a replacement for the SMN2-targeted background therapies that address the underlying survival motor neuron gene deficiency. Approval was based on Phase 3 SAPPHIRE trial data demonstrating motor function improvement (Hammersmith Functional Motor Scale Expanded score) at 12 months versus placebo in patients on stable SMN2-directed therapy. The FDA granted Fast Track, Orphan Drug, and Rare Pediatric Disease designations. Scholar Rock reported net product sales of $0 (pre-launch) as of Q2 2026 with priced at approximately $310,000 per patient annually.