FDA approves Scholar Rock's apitegromab for SMA as muscle-preservation race widens

The FDA approved Scholar Rock's apitegromab on September 11, 2026, for adults and children with spinal muscular atrophy (SMA) who have already been treated with existing therapies, the company's first regulatory approval ^[2]. The injectable is sold as Isembyld and selectively blocks activation of myostatin, a protein that limits muscle growth, with the aim of increasing muscle mass and strength ^[2].

The approval was based on late-stage data showing the therapy significantly improved motor function compared with placebo, Reuters reported ^[2]. SMA is a genetic disorder that damages motor neurons, causing progressive muscle weakness and problems with movement, breathing and swallowing; it is estimated to affect roughly 10,000 children and adults in the United States, according to the Muscular Dystrophy Association ^[2]. Scholar Rock said the drug will be available in the coming days but did not immediately respond to a request for comment on pricing details ^[2]. The company's shares rose more than 23% in after-market trading, and BMO Capital Markets analyst Evan Seigerman forecasts 2035 adjusted worldwide peak sales of $2.1 billion ^[2]. Isembyld will compete with Biogen's Spinraza, Novartis' gene therapy Zolgensma and Roche's oral Evrysdi ^[2].

Getting there took a detour. A Complete Response Letter in September 2025 concerned the third-party facility handling fill-finish operations rather than apitegromab itself; after resubmission and a change of manufacturing site, the FDA action date was set at September 30, 2026 ^[1]. The approval ultimately arrived earlier, on September 11 ^[2].

The obesity programs behind the approval

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 ^[2]. In the phase 2 EMBRAZE trial, apitegromab combined with tirzepatide (sold as Mounjaro and Zepbound) produced 54.9% greater relative lean mass retention than tirzepatide plus placebo across 102 participants over 24 weeks ^[1].

Eli Lilly's bimagrumab blocks the activin type II receptor directly rather than myostatin alone. In the phase 2b BELIEVE trial, which enrolled 507 participants across nine treatment arms, the highest-dose combination of bimagrumab and semaglutide (sold as Ozempic, Wegovy and Rybelsus) produced 22.1% total body weight loss at 72 weeks, compared with 15.7% for semaglutide alone, with about 92% of the combination group's weight loss coming from fat mass ^[1]. Lean mass loss was 2.9%, against 7.4% with semaglutide alone, and bimagrumab by itself increased lean mass 2.5% above baseline ^[1]. Lilly halted a separate phase 2b trial testing bimagrumab alongside tirzepatide in patients with type 2 diabetes in September 2025, citing strategic business reasons, while confirming a parallel obesity-only trial continues, with results expected later this year ^[1].

Regeneron's trevogrumab targets myostatin; garetosmab, tested alongside it in some arms, targets activin A. In the ongoing phase 2 COURAGE trial, 26-week data presented at the European Association for the Study of Diabetes in September 2025 showed adding trevogrumab to semaglutide prevented roughly half the lean mass loss typically seen with semaglutide alone while increasing fat loss ^[1]. The three-drug arm told a better body-composition story and a worse tolerability one: lean mass was just 7.4% of total weight loss versus 33.0% with semaglutide alone, and fat loss made up 92.6% of the weight loss versus 67.0% ^[1]. Regeneron reported a "substantially higher" rate of discontinuations for tolerability reasons in that arm without giving an exact figure ^[1]. COURAGE is expected to complete in late 2026 ^[1].

Biohaven's taldefgrobep alfa blocks activin receptor signaling triggered by myostatin and multiple activins. Its phase 3 SMA trial missed its primary endpoint, and a phase 2 proof-of-concept study as monotherapy completed enrollment in March 2026, with topline data expected in the second half of this year and no efficacy results published to date ^[1].

Why it matters for patients

No drug is approved to preserve muscle during GLP-1 treatment. The SMA approval does not change that, and none of the obesity combinations described above has completed the trials required for approval in that use ^[1]. The apitegromab approval is the first time regulators have cleared a drug from this mechanism, which is the clearest signal so far that blocking myostatin can work in people ^[1][2].

Patients weighing muscle loss during weight loss currently have no approved drug option, and the candidates differ in ways that will matter if they reach the market: myostatin-selective drugs have shown cleaner tolerability so far, while broader receptor blockade has shown larger effects on lean mass — and, in one arm, more dropouts ^[1].

What happens next

COURAGE is due to complete in late 2026 ^[1]. Results from Lilly's obesity-only bimagrumab trial are expected later this year ^[1]. Topline taldefgrobep data are expected in the second half of 2026 ^[1]. No timeline for filing apitegromab for a muscle-preservation indication alongside a GLP-1 medication has been disclosed.