ISEMBYLD (apitegromab-mstn) - (SAPPHIRE)

September 11, 2026: Scholar Rock (NASDAQ: SRRK) said the FDA approved ISEMBYLD (apitegromab-mstn) for spinal muscular atrophy in adults and children age 2+ who are currently receiving an SMN2-targeted treatment. The company said it has begun the U.S. commercial launch, with product expected to ship in the coming days, and received a Rare Pediatric Disease Priority Review Voucher.

Approval was based on the Phase 3 SAPPHIRE trial. In the main efficacy population (ages 2-12, n=103), ISEMBYLD 10 mg/kg plus background SMN2-targeted therapy met the primary endpoint, showing a 2.2-point improvement vs placebo on HFMSE at one year (nominal p=0.0121). A greater proportion of treated patients achieved at least a 3-point HFMSE increase versus placebo, 34.2% vs 13.5% (odds ratio 3.8; nominal p=0.0125). The trial enrolled 188 patients ages 2-21 receiving nusinersen or risdiplam.

Common adverse reactions included upper respiratory tract infections, vomiting, cough, viral infections, headache, gastroenteritis, pharyngitis, and hypersensitivity; fractures occurred in 9% of patients on ISEMBYLD 10 mg/kg vs 2% on placebo. Scholar Rock will host an investor call on September 14, 2026.