Isembyld cleared for spinal muscular atrophy
- Sponsor
- Scholar Rock $SRRK
- Drug
- ISEMBYLD · apitegromab-mstn
- Indication
- 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 (add-on to Spinraza or Evrysdi)
FDA approved Scholar Rock's Isembyld (apitegromab-mstn) as the first muscle-targeted therapy for spinal muscular atrophy, as an add-on for patients 2+ on SMN2-targeted maintenance therapy.
What this means
Spinal muscular atrophy (SMA) is a genetic disease in which motor neurons that control muscle movement progressively die off, causing weakness and loss of function. The three FDA-approved therapies for SMA — Spinraza (nusinersen), Evrysdi (risdiplam), and Zolgensma (onasemnogene abeparvovec) — all target the SMN gene defect that causes the disease, but none directly rebuilds the muscle that has already atrophied. ISEMBYLD (apitegromab-mstn) is a Scholar Rock antibody that blocks myostatin, a natural brake on muscle growth; releasing that brake helps skeletal muscle regrow while the SMN-targeting therapy keeps the underlying disease in check. On September 11, 2026 the FDA approved ISEMBYLD as an add-on for adults and children two years and older who are currently receiving an SMN2-targeted maintenance therapy — Spinraza or Evrysdi. Approval was supported by the SAPPHIRE Phase 3 trial (N=188 patients ages 2-21 across nine countries): 34.2% of ISEMBYLD patients gained three or more points on the Hammersmith Functional Motor Scale Expanded (HFMSE) versus 13.5% on placebo. ISEMBYLD is the first and only muscle-targeted therapy for SMA.