SRRK Stock Hub: Scholar Rock News, ISEMBYLD Launch and Safety

On September 11, 2026 Scholar Rock announced that the FDA had approved ISEMBYLD (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. The recommended dose is 10 mg/kg by intravenous infusion. The filings record the announcement date rather than the date on the approval letter, and the label is dated only “Issued: 09/2026”. The announcement came nineteen days before the September 30 PDUFA action date, and Scholar Rock was awarded a Rare Pediatric Disease Priority Review Voucher with it.

The shares fell 14.93 per cent over the month containing the approval, according to market data as of September 30, 2026. The approval itself had been widely expected after a resubmission with a September 30 action date, so the market was pricing what comes next: nominal rather than multiplicity-controlled p-values on the pivotal result, only 53 patients given the approved 10 mg/kg dose, all of them non-ambulatory children aged 2 to 12, against a label that covers adults and carries no such restrictions, a labelled fracture warning at 9 per cent against 2 per cent on placebo, an FDA post-marketing requirement and a separate FDA request that management initially denied existed, and no product revenue or disclosed price yet.

On the September 14 investor call management said the FDA had not required any post-marketing safety commitments regarding bone or reproductive safety. The next day, on September 15, the company filed a Form 8-K stating this was said in error. The filing distinguishes two things: the FDA outlined a post-marketing requirement that the company establish a pregnancy safety study to collect and analyse pregnancy complications and birth outcomes in exposed pregnancies, and separately requested that all serious and non-serious domestic and foreign fracture cases be submitted as 15-day alert reports.

In SAPPHIRE, fractures occurred in 5 of 53 patients (9 per cent) on the approved 10 mg/kg dose and 3 of 53 (6 per cent) on twice that dose, against one patient of 53 on placebo (2 per cent) — a difference of four events. Femur fractures occurred in three treated patients and no patient discontinued because of a fracture. In the ongoing open-label extension, where every patient receives 20 mg/kg, fractures occurred in 22 patients (9 per cent) including five serious femoral events. In Warnings and Precautions the label tells prescribers to use the drug with caution in patients with a history of low bone density or multiple fractures and, in patients who fracture, to weigh the risks and benefits of continuing; it adds that animal studies have also demonstrated adverse effects in bone. The FDA’s request for 15-day alert reports on every fracture case worldwide, serious or not, indicates how closely the agency intends to watch it.

At June 30, 2026 it held $437.1 million of cash and equivalents plus $55.0 million of marketable securities, $492.1 million combined, against $367.6 million at December 31, 2025. First-half operating cash use was $152.4 million and the first-half net loss was $215.4 million. The company has drawn $200.0 million of a $350 million Blue Owl facility — $100 million in February 2026, used to repay $103.7 million of Oxford obligations, and $100 million on March 31, 2026 — and the facility requires unrestricted cash of at least 60 per cent of outstanding principal unless milestones are met, which on that balance is $120 million. A new $200 million ATM prospectus supplement was filed on August 6, 2026. The company expects its resources to fund operations into the second half of 2027.