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• This was Scholar Rock’s second try at approval after a rejection last year. 
• Scholar Rock said commercial supply is ready and the U.S. launch begins immediately, with product shipping in the coming days. 
• The company is also planning to seek approval for the drug in Europe and Japan.

The U.S. Food and Drug Administration (FDA) on Friday said that it approved Scholar Rock’s (SRRK) Isembyld, the first treatment designed to target muscle loss in spinal muscular atrophy, ahead of a September 30 deadline.  

The stock jumped 15% after hours at the time of writing after trading flat in the regular session.

SMA is a rare genetic disease that weakens the arms, legs, and muscles used to breathe and swallow. It affects about 1 in 10,000 births and roughly 10,000 people in the United States.

A First For Muscle Loss

Isembyld is the first SMA medicine aimed at muscle itself rather than the nerve cells that control it. It is cleared for patients aged two and older who already take certain existing SMA drugs. Those older medicines help keep motor nerves alive, but many patients still lose strength. Isembyld blocks myostatin, a protein that normally limits muscle growth. It is given by vein every four weeks.

In a one-year study of 188 patients ages two to 21 who could not walk on their own, Isembyld-treated patients improved on a standard motor-function test while those on placebo declined. The main analysis covered 156 children ages two to 12 and found a 1.8-point average gain versus placebo. Among that group, 34.2% on the drug had a meaningful gain, versus 13.5% on placebo.

Scholar Rock said commercial supply is ready and the U.S. launch begins immediately, with product shipping in the coming days. Isembyld is the company’s first and only approved drug.

Delayed Path To Approval

This was Scholar Rock’s second try. The FDA rejected the first filing in September 2025, not because of problems with the drug’s trial results, but because of quality issues at a contract plant in Indiana, now owned by Danish drugmaker Novo Nordisk, that handled the final filling of vials.

Scholar Rock resubmitted in March 2026 and named a second U.S. plant as backup. After another poor inspection of the Indiana site this spring, the company dropped that plant and proceeded only with the alternate facility.

In Europe, Scholar Rock withdrew its application in August over the same plant issue and plans to refile with the backup facility. A Japan filing is targeted by year-end after regulators said no extra local trials are needed.

Beyond SMA in older children, Scholar Rock is running a study in infants under two and has begun a mid-stage trial in facioscapulohumeral muscular dystrophy, another rare muscle-wasting disease, which recently received fast-track status.

How Did SRRK Retail Traders React?

On Stocktwits, retail sentiment around SRRK stock jumped from ‘neutral’ to ‘bullish’ over the past 24 hours, while message volume stayed at ‘normal’ levels.

SRRK stock has gained 26% year-to-date. 

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