FDA Approves Scholar Rock's Isembyld (Apitegromab) as first Muscle-Targeted Treatment for Spinal Muscular Atrophy (SMA)
On September 11, 2026, the U.S. Food and Drug Administration (FDA) approved Scholar Rock’s 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 (such as nusinersen or risdiplam). This landmark decision establishes Isembyld as the first and only approved muscle-targeted therapy for SMA, addressing the critical unmet need of progressive muscle weakness and motor decline that persists despite treatment with SMN-targeted therapies.
In conjunction with the approval, the FDA awarded Scholar Rock a Rare Pediatric Disease Priority Review Voucher (PRV).1
The approval was supported by positive results from the pivotal Phase 3 SAPPHIRE trial, along with long-term data from the TOPAZ and ONYX studies, which demonstrated that adding Isembyld to standard SMN-targeted treatments leads to statistically significant and clinically meaningful improvements in motor function.
What It Means
Unlike existing SMA therapies that focus on correcting the survival motor neuron (SMN) protein deficiency to prevent motor neuron loss, Isembyld selectively blocks the activation of myostatin (specifically pro- and latent myostatin), a protein that naturally limits muscle growth. By targeting muscle tissue directly, Isembyld aims to increase muscle mass and strength, offering a complementary mechanism of action that can be used alongside standard-of-care SMN2-directed therapies. This represents a paradigm-shifting milestone for the SMA community, providing a therapeutic option directly aimed at restoring and preserving physical mobility.
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An instance of Rare disease pipelines only accelerate through early FDA alignment and breakthrough designations. — Scholar Rock utilized the FDA's rare disease voucher framework to clear its muscle-targeted treatment for spinal muscular atrophy. ↩︎