TL;DR: The U.S. Food and Drug Administration approved Scholar Rock's Isembyld on Friday, September 11, 2026, for adults and children age 2 and older with spinal muscular atrophy who are already receiving SMN2-targeted treatment.

The U.S. Food and Drug Administration approved Scholar Rock's therapy on Friday, September 11, 2026, to treat spinal muscular atrophy, a rare genetic condition that causes muscle weakness, according to Reuters reporting carried by KSL.com. The decision marked the first regulatory approval for Scholar Rock, the Cambridge, Massachusetts biopharmaceutical company listed on Nasdaq under ticker SRRK. The injectable treatment, sold as Isembyld and chemically known as apitegromab, is the first muscle-targeted therapy designed to improve motor function for adults and children with spinal muscular atrophy who have been treated with existing therapies for the condition. Scholar Rock said Isembyld will be available in the coming days, with product available to ship in the coming days and a dedicated Scholar Rock Supports team now available to assist patients and caregivers, according to the company's announcement reported by Drugs.com.

What the FDA approved on September 11

The FDA approval covers Isembyld, identified as apitegromab-mstn, for the treatment of spinal muscular atrophy in adults and children two years of age and older who are currently receiving a survival motor neuron 2-targeted treatment, according to Drugs.com. The approval was reported on Sept. 11 by Reuters reporting carried by KSL.com, which described the action as approval of Scholar Rock's therapy on Friday to treat a rare genetic condition that causes muscle weakness. KSL.com reported that the approval marked the first regulatory approval for the company. Scholar Rock announced the approval on September 11, 2026, from Cambridge, Massachusetts, identifying itself as a global biopharmaceutical company focused on rare, severe and debilitating neuromuscular diseases through myostatin biology, according to Drugs.com.

The treatment is administered as an injectable treatment, according to KSL.com. The Muscular Dystrophy Association described Isembyld as a monthly infusion treatment for people living with spinal muscular atrophy who are currently receiving a survival motor neuron 2-targeted treatment. The recommended dose is 10 mg/kg, which was the dose evaluated for efficacy in the Phase 3 SAPPHIRE study and cited in the approval announcement, according to Drugs.com. Scholar Rock was awarded a Rare Pediatric Disease Priority Review Voucher with the approval of Isembyld, which may be used to obtain priority review for a future marketing application, according to Drugs.com.

Who the treatment is for

Isembyld is approved for use in all adults and children age 2 and older with spinal muscular atrophy who are currently receiving a survival motor neuron 2-targeted treatment, according to Drugs.com. KSL.com described the eligible group as adults and children with spinal muscular atrophy who have been treated with existing therapies for the condition. The Muscular Dystrophy Association described the approved use as treatment for people living with spinal muscular atrophy who are currently receiving a survival motor neuron 2-targeted treatment. Scholar Rock described Isembyld as the first and only muscle-targeted treatment to demonstrate motor function improvement in individuals with spinal muscular atrophy currently receiving an SMN2-targeted treatment, according to Drugs.com.

Spinal muscular atrophy is a genetic disorder that damages motor neurons, causing progressive muscle weakness and problems with movement, breathing and swallowing, according to KSL.com. Drugs.com described spinal muscular atrophy as a rare, severe neuromuscular disease that results in irreversible loss of motor neurons and progressive muscle wasting, causing continuous motor function decline throughout life and diminishing the independence of both adults and children. The condition is estimated to affect roughly 10,000 children and adults in the United States, according to the Muscular Dystrophy Association as cited by KSL.com. The Muscular Dystrophy Association said spinal muscular atrophy is a leading genetic cause of death in infants and often requires lifelong support to maintain mobility, breathing and independence.

How the SAPPHIRE trial supported approval

The approval was based on late-stage data that showed the therapy significantly improved motor function for patients with the condition compared with placebo, according to KSL.com. Drugs.com reported that the approval was based on positive results from the Phase 3 pivotal, randomized, double-blind, placebo-controlled SAPPHIRE study. The SAPPHIRE study met its primary endpoint, according to Drugs.com. In the study, individuals receiving Isembyld demonstrated improvement in motor function after one year of treatment while those on an SMN2-targeted treatment alone experienced a loss of motor function, according to Drugs.com.

The main efficacy population in SAPPHIRE included patients 2 to 12 years of age, with 103 participants, according to Drugs.com. All patients in the efficacy comparison were receiving SMN2-targeted background therapy, according to Drugs.com. Patients receiving Isembyld 10 mg/kg and an SMN2-targeted treatment showed a 2.2-point improvement in the Hammersmith Functional Motor Scale-Expanded, described as the gold-standard measure of motor function, compared with patients receiving an SMN2-targeted treatment alone at one year, with a nominal p-value of 0.0121, according to Drugs.com. KSL.com described the same late-stage result as significantly improved motor function compared with placebo.

An additional efficacy measure showed that 34.2% of Isembyld-treated patients had a 3-point or greater increase in Hammersmith Functional Motor Scale-Expanded scores compared with 13.5% of placebo-treated patients, with an odds ratio of 3.8 and a nominal p-value of 0.0125, according to Drugs.com. Scholar Rock described the 2.2-point improvement as robust and clinically meaningful, according to Drugs.com. The Muscular Dystrophy Association said Isembyld was approved based on positive results from the pivotal Phase 3 SAPPHIRE study, supported by earlier studies including TOPAZ and ONYX, which demonstrated clinically meaningful improvements in motor function for people living with spinal muscular atrophy. The association also noted that additional analyses from SAPPHIRE, including outcomes in nonambulatory people with Type 2 or Type 3 spinal muscular atrophy, were presented at the 2026 MDA Clinical & Scientific Conference in a poster titled Post hoc analyses from the Phase 3 SAPPHIRE study evaluating apitegromab in patients with nonambulatory type 2 or 3 spinal muscular atrophy.

Safety findings from the clinical program

Isembyld has a well-characterized safety profile based on a safety database that includes more than 500 individuals across all apitegromab clinical studies globally, some of whom have been on treatment for more than seven years, according to Drugs.com. Ninety-eight percent of participants treated in SAPPHIRE elected to continue in the ONYX long-term extension study, according to Drugs.com. The Muscular Dystrophy Association identified ONYX as one of the studies supporting the SAPPHIRE results, alongside TOPAZ.

In the SAPPHIRE study, the most common adverse reactions were upper respiratory tract infections, vomiting, cough, other viral infections, headache, gastroenteritis, pharyngitis and hypersensitivity, according to Drugs.com. Fractures occurred in 9% of patients treated with Isembyld 10 mg/kg compared with 2% in the placebo group in SAPPHIRE, according to Drugs.com. The company announcement reported by Drugs.com directed readers to Important Safety Information for further information. The safety database span of more than seven years for some participants provides longer-term exposure data within the apitegromab clinical program, according to Drugs.com.

How Isembyld works on muscle

Chemically known as apitegromab, Isembyld selectively blocks activation of myostatin, a protein that limits muscle growth, with the aim of increasing muscle mass and strength, according to KSL.com. Drugs.com described Isembyld as the first and only muscle-targeted treatment to demonstrate motor function improvement in individuals with spinal muscular atrophy currently receiving an SMN2-targeted treatment. The Muscular Dystrophy Association described Isembyld as the first and only muscle-targeted therapy for spinal muscular atrophy. Scholar Rock identified myostatin biology as its leading platform for improving the lives of patients with rare, severe and debilitating neuromuscular diseases, according to Drugs.com.

Scholar Rock Chairman and Chief Executive Officer David L. Hallal said Today's FDA approval of Isembyld marks a defining moment for the SMA community as the company launches the world's first-ever muscle targeted treatment for children and adults living with SMA in the U.S., according to Drugs.com. Hallal also said Scholar Rock had delivered a therapeutic breakthrough with Isembyld after decades of failed industry-wide efforts to unlock the potential of myostatin inhibition, according to Drugs.com. Cure SMA President Kenneth Hobby said the approval of Isembyld as the first-ever treatment to directly target the muscular component of SMA is a significant turning point for adults and children who have been waiting for innovative therapeutic options to improve motor function, according to Drugs.com. Hobby also said improving motor function is a significant unmet need that must be addressed with urgency and that such improvements are fundamental to maintaining independence and to enabling participation in important activities of daily living from self-care to work and social interactions, according to Drugs.com.

Where Isembyld fits among existing SMA drugs

Isembyld will compete with Biogen's Spinraza, Novartis' gene therapy Zolgensma and Roche's oral Evrysdi, according to KSL.com. KSL.com described Isembyld as the first muscle-targeted therapy designed to improve motor function for patients who have been treated with existing therapies. Drugs.com described Isembyld as the first and only muscle-targeted treatment to demonstrate motor function improvement in individuals currently receiving an SMN2-targeted treatment, while those on an SMN2-targeted treatment alone experienced a loss of motor function in SAPPHIRE. The Muscular Dystrophy Association said Isembyld was designed to improve muscle function in people living with spinal muscular atrophy who are already on SMN-targeted therapies, addressing the continued unmet need of motor decline.

Pediatric neurologist Randal Richardson, MDA Care Center Director at Gillette Children's Hospital in Saint Paul, Minnesota, said the era of stopping or slowing SMA progression has evolved to a new one focused on improving function, according to the Muscular Dystrophy Association. Richardson described Isembyld as the first muscle-directed therapy that can work alongside SMN-enhancing treatments that have transformed care in recent years, according to the Muscular Dystrophy Association. MDA Chief Research Officer Angela Lek said Muscular Dystrophy Association has strategically invested in pioneering science and built a research ecosystem that enables scientific discoveries to be translated into disease modifying drugs for patients, according to the Muscular Dystrophy Association. The Muscular Dystrophy Association said the approval reflects recognition that Isembyld represents a significant improvement in treatment.

Commercial launch and manufacturing plans

Scholar Rock's U.S. commercial launch was underway at the time of the September 11 announcement, with product available to ship in the coming days, according to Drugs.com. KSL.com reported that the company said Isembyld will be available in the coming days. Scholar Rock Supports, a dedicated support team, was reported as now available to assist patients and caregivers, according to Drugs.com. Hallal said the company's U.S. commercial team is now engaging physicians, SMA care teams and payers on behalf of the SMA community, according to Drugs.com. Hallal thanked clinical study investigators, Cure SMA and other patient advocacy groups for dedication and support, and thanked patients and families affected by spinal muscular atrophy who participated in clinical trials, according to Drugs.com.

The company has previously said it would use a U.S.-based manufacturing facility for Isembyld, according to KSL.com. Scholar Rock shares rose over 23% in after-market trading following the approval, according to KSL.com. The company did not immediately respond to a Reuters request for comment on pricing details, according to KSL.com. Management was scheduled to host an investor call Monday, September 14, 2026, at 8:00 a.m. ET, according to the StockTitan record of the company announcement. With the approval, Scholar Rock was awarded a Rare Pediatric Disease Priority Review Voucher, which may be used to obtain priority review for a future marketing application, according to Drugs.com.

Analyst expectations and broader research

Cantor analysts said Isembyld's approval sets up Scholar Rock to be one of the best long-term growth stories in biotech based on geographic, indication and product line expansions, according to KSL.com. BMO Capital Markets analyst Evan Seigerman forecasts 2035 adjusted worldwide peak sales of $2.1 billion for the drug, according to KSL.com. Scholar Rock is also testing the drug to preserve muscle in obesity, competing with more than a dozen companies developing treatments aimed at minimizing muscle loss during weight loss, according to KSL.com.

The Muscular Dystrophy Association said its approval milestone builds on more than 75 years of legacy, during which the association has funded research that has led to nearly every approved therapy for neuromuscular diseases, including Isembyld. MDA said it has invested more than $1.2 billion in research, including over $50 million in spinal muscular atrophy, helping pave the way for more than 30 FDA-approved treatments in the last decade. MDA said today's approval underscores its role through advocacy, its nationwide MDA Care Center Network at over 150 top medical institutions, as well as the MDA Resource Center and Gene Therapy Support Network. University of Connecticut School of Medicine and The Jackson Laboratory researcher Se-Jin Lee said Muscular Dystrophy Association support was pivotal in early research on myostatin biology and demonstration that blocking it could profoundly increase muscle growth, according to the Muscular Dystrophy Association.

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