Scholar Rock has received U.S. Food and Drug Administration approval for apitegromab, an injectable monoclonal antibody that will be marketed as Isembyld, for the treatment of spinal muscular atrophy (SMA). The approval marks the first FDA-cleared product for Scholar Rock and makes Isembyld the first therapy approved to directly target muscle loss associated with the rare genetic disorder.
The treatment is approved for adults and children aged two years and older who are already receiving therapies that target the SMN2 gene. Scholar Rock said the product has begun launching following the approval and is expected to ship in the coming days.
Approval Based on Phase 3 SAPPHIRE Trial Results
The FDA’s decision was supported by findings from Scholar Rock’s phase 3 SAPPHIRE study, which evaluated Isembyld in combination with SMN2-targeted therapies. According to the company, patients who received the combination treatment for one year experienced improvements in motor function, while patients receiving SMN2-targeted therapy alone showed motor decline.
Data from the study showed a statistically significant and clinically meaningful 2.2-point improvement on the Hammersmith Functional Motor Scale-Expanded among patients treated with Isembyld alongside an SMN2 therapy compared with those receiving SMN2 treatment alone. More than one-third of patients receiving Isembyld achieved an improvement of at least three points on the scale.
Scholar Rock also reported that 98% of participants chose to continue into the long-term extension study following completion of the trial.
The FDA issued its approval about two weeks before the drug’s original September 30 Prescription Drug User Fee Act deadline.
“We are now able to directly target the muscle, not just the motor neuron, for people living with SMA,” said Basil Darras, M.D., director of the Neuromuscular Center and Spinal Muscular Atrophy Program at Boston Children’s Hospital and a principal investigator in the SAPPHIRE study.
Treatment Targets Muscle Loss in SMA
SMA is a rare genetic disease that affects approximately 10,000 children and adults in the United States. The condition causes irreversible damage to motor neurons, resulting in progressive muscle wasting and loss of movement. In its most severe forms, SMA is fatal to infants.
Unlike existing SMA therapies that act on the SMN2 gene, Isembyld works by selectively blocking activation of myostatin, a protein that limits skeletal muscle growth. The treatment can be used alongside SMN2-targeting therapies.
There was no treatment available for SMA until 2016. Since then, the FDA has approved a gene therapy from Novartis, an oral medication from Roche, and Biogen’s injectable gene-targeted therapy. Those treatments act on the SMN2 gene and can be used in combination with Isembyld.
Regulatory Setback and Commercial Launch
Scholar Rock initially submitted its application for approval in September 2025. The FDA later declined the application because of issues linked to a fill-finish facility in Bloomington, Indiana. In August 2026, the company removed that facility from its U.S. application after the FDA classified it as Official Action Indicated.
The company said the net annual cost of Isembyld for a typical patient will be about $310,000, although the amount may vary depending on patient weight and insurance coverage. A single-use vial has a wholesale acquisition cost of $11,659. Company executives said a typical patient weighing between 35 kilograms and 45 kilograms is expected to receive about three vials every four weeks.
Chief Operating Officer Keith Woods said the company expects a steady and consistent pace of patient starts as the company serves a gradually increasing number of children and adults living with SMA.
Scholar Rock is also evaluating the drug’s ability to preserve lean muscle mass in patients receiving obesity treatment.
Scholar Rock shares rose more than 23% in after-market trading on Friday following the approval and were about 5% higher before the bell on Monday.
Isembyld represents a different therapeutic approach to spinal muscular atrophy because it directly targets the muscle component of the disease. Existing SMN2-targeted therapies primarily work to increase production of functional survival motor neuron protein, while Isembyld is designed to address muscle loss alongside those treatments.
SMA is a rare and progressive neuromuscular disorder associated with muscle weakness and wasting. According to the FDA, the disease results from problems involving the SMN1 gene and can lead to progressive loss of motor function.
Clinical Evidence Supporting Isembyld
The FDA approval was supported by data from the 52-week SAPPHIRE study, a randomized, double-blind, placebo-controlled clinical trial involving 188 participants with SMA. Participants were already receiving an approved SMN2-targeted treatment.
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