Scholar Rock Holding Corporation announced on September 11, 2026, that the U.S. Food and Drug Administration (FDA) has approved ISEMBYLD (apitegromab-mstn) for the treatment of spinal muscular atrophy (SMA) in adults and children two years of age and older who are currently receiving a survival motor neuron 2 (SMN2)-targeted treatment. The filing indicates that ISEMBYLD is the first and only muscle-targeted treatment approved for this population.
The approval is based on results from the Phase 3 randomized, placebo-controlled SAPPHIRE study. In this study, patients receiving the recommended dose of 10 mg/kg of ISEMBYLD demonstrated a 2.2-point improvement in motor function as measured by the Hammersmith Functional Motor Scale-Expanded (HFMSE) compared to those receiving an SMN2-targeted treatment alone. Specifically, 34.2% of patients treated with ISEMBYLD showed a greater than or equal to 3-point increase in HFMSE, compared to 13.5% of patients on placebo.
Scholar Rock stated that the U.S. commercial launch of ISEMBYLD is underway, with product available to ship in the coming days. The company has launched a patient support program called Scholar Rock Supports to assist patients and caregivers with insurance coverage, financial assistance, and treatment logistics. The company also noted that it was awarded a Rare Pediatric Disease Priority Review Voucher in connection with the approval.
The filing details the safety profile of the treatment, noting that fractures occurred in 9% of patients treated with ISEMBYLD 10 mg/kg versus 2% in the placebo group. Common adverse reactions included upper respiratory tract infections, vomiting, cough, viral infections, headache, gastroenteritis, pharyngitis, and hypersensitivity.
Scholar Rock will host a conference call and webcast on September 14, 2026, at 8:00 a.m. Eastern Time to discuss the approval and presentation materials.
