FDA Approves Isembyld (Apitegromab): First Muscle-Targeted Therapy for Spinal Muscular Atrophy
On September 11, 2026, the FDA approved Scholar Rock's Isembyld (apitegromab-mstn) — the first therapy for spinal muscular atrophy (SMA) that directly targets the muscle side of the disease, and the first-ever FDA approval for Scholar Rock. It is approved as a monthly IV infusion add-on for adults and children ≥2 years of age who are already receiving an SMN2-targeted treatment (nusinersen or risdiplam). The FDA's announcement states: "Isembyld is the first therapy approved for SMA that directly targets muscle loss, working alongside existing treatments to address a critical dimension of the disease."
The approval rests on the Phase 3 SAPPHIRE study (188 patients, 9 countries, all on background SMN2-targeted therapy). Per Scholar Rock's press release: "In the Phase 3 randomized, placebo-controlled SAPPHIRE study, individuals receiving ISEMBYLD demonstrated a robust, clinically meaningful improvement in motor function after one year of treatment while those on an SMN2-targeted treatment alone experienced a loss of motor function." Specifically, the 10 mg/kg dose showed a 2.2-point HFMSE advantage at one year (nominal p=0.0121; main efficacy population ages 2–12, n=103), and 34.2% of treated patients gained ≥3 points vs 13.5% of placebo (odds ratio 3.8; nominal p=0.0125). Notable safety signal: fractures occurred in 9% of treated patients vs 2% on placebo.
CEO David Hallal framed it as the end of a decades-long quest: "Today's FDA approval of ISEMBYLD marks a defining moment for the SMA community as we now launch the world's first-ever muscle targeted treatment for children and adults living with SMA in the U.S. … After decades of failed industry-wide efforts to unlock the potential of myostatin inhibition, Scholar Rock has delivered a therapeutic breakthrough." The approval also earned Scholar Rock a Rare Pediatric Disease Priority Review Voucher. Reporting puts the net price at about $310,000 per year (Citeline), and Scholar Rock subsequently clarified the FDA required post-marketing safety commitments. This approval resolves the regulatory path tracked in the prior manufacturing de-risking (Catalent Indiana removed from the filings in August 2026 — see Scholar Rock's Apitegromab Secures FDA Fast Track in FSHD and Commences Phase 2 FORGE Trial Amid Pending SMA Review).