In what signifies the end of a challenging regulatory journey, Scholar Rock secured an FDA approval for its spinal muscular atrophy treatment, apitegromab.
The injectable monoclonal antibody, marketed as Isembyld, joins a handful of other SMA therapies, but it is the first to treat muscle atrophy in these patients, according to the FDA. It is also the first approval of any product for Scholar Rock.
Isembyld was cleared for use in adults and children two and older who are also receiving treatments that targets the SMN2 gene, which helps patients with SMA replace some of the vital neuroprotective proteins they’re missing. The treatment, which is set to “ship in the coming days” is projected to cost $310,000 annually.
The FDA approval was based on Scholar Rock’s phase 3 Sapphire study that showed Isembyld, plus SM2-targeted treatment, increased motor function after a year, while patients on SMN2 therapy alone had motor loss.
According to the data, patients who received Isembyld with an SMN2 therapy for a year experienced a significant and clinically meaningful 2.2-point improvement on the Hammersmith Functional Motor Scale-Expanded, a scale used to capture motor function, compared to patients on SM2 therapy alone. More than one-third of patients on Isembyld showed 3-point or greater improvement in motor function. Nearly all (98%) of patients in the trial elected to continue with Scholar Rock’s long-term extension study.
The decision to approve came two weeks ahead of the drug’s original September 30 PDUFA 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.
Scholar Rock originally filed for approval in September 2025. Its application was however denied by the regulator, citing problems at a the fill-finish Catalent site in Bloomington, Indiana. Scholar Rock dropped the facility from its U.S. application in August 2026 after the FDA classified the facility as Official Action Indicated (OAI).
SMA is rare genetic disease that affects roughly 10,000 children and adults in the U.S. The disease is marked by irreversible damage to motor neurons which ultimately causes muscle wasting and progressive loss of movement. In its most severe forms, SMA is fatal to infants. There was no treatment for the condition until 2016.
Over the last decade, however, things have changed as the FDA has approved a gene-therapy from Novartis, an oral medication from Roche, and Biogen’s injectable gene-targeted therapy. The latter treatments act on the SMN2 gene meaning they can be used in combination with Isembyld. For its part, Isembyld intervenes by blocking myostatin, a protein that limits skeletal muscle growth, to preserve strength.
Scholar Rock is also testing the drug’s ability to preserve lean muscle mass in patients receiving obesity treatment.
The company's shares rose over 23% in after-market trading Friday on the news.