FDA Grants Priority Review BLA for Spinal Muscular Atrophy Drug, Apitegromab

Scholar Rock announced today that the FDA granted priority review for a biologics license application (BLA) for apitegromab, a treatment for spinal muscular atrophy (SMA), according to a news release. If approved, apitegromab would be the first muscle-targeted treatment for people living with SMA. A Prescription Drug User Fee Act target action date has been set for Sept. 22, 2025.

“We are delighted with the priority review designation for apitegromab, which is consistent with the potential of apitegromab to be a transformative therapy and the first muscle-targeted treatment for people living with SMA who continue to have decline in motor function despite receiving SMN-targeted treatments,” Jay Backstrom, M.D., M.P.H, president and CEO of Scholar Rock, said in the release. “In addition to the positive news from the FDA, we are pleased with the parallel acceptance of the MAA by the EMA and look forward to continue to work with regulatory agencies to bring apitegromab to the SMA community as we prepare for our global commercial launch, starting with the U.S.”

Apitegromab submissions are based on efficacy and safety data from the phase 3 SAPPHIRE trial, which enrolled 156 SMA patients ages 2 to 12. Patients were randomized to receive apitegromab 10 mg/kg, apitegromab 20 mg/kg, or placebo by intravenous (IV) infusion every 4 weeks for 12 months. Success was measured using the expanded Hammersmith Functional Motor Scale, which gathers information based on the performance of 20 scored activities such as sitting, standing and crawling. If a patient cannot complete the movement, they are given a 0. If the patient completes the movement with some assistance, they are given 1 point and if they can do the movement with no help, they get 2 points. More than a quarter (30.4%) of patients given apitegromab had a greater than 3-point increase on the Hammersmith Functional Motor Scale Expanded, compared with 12.5% of patients on placebo, the trial data shows. There were no serious adverse events recorded.

Spinal muscular atrophy is a rare genetic disease characterized by a genetic mutation in the fifth chromosome, in a gene called SMN1. It affects approximately 30,000 to 35,000 people across the United States and Europe. There are five types of SMA, ranging from type 0 to type 4. The most common symptom is weakness in the shoulders, hips, thighs and upper back, with lower limbs seeming to be more affected than the upper limbs. The most dangerous complication for SMA patients is a potential breathing disruption caused by trunk muscle weakness. Typically, the later the onset of symptoms, the milder the disease course. For example, it is the most common cause of mortality in infants.

Apitegromab is a fully human monoclonal antibody. It inhibits myostatin activation, a protein that regulates muscle growth, by selectively binding the pro- and latent forms of myostatin in the skeletal muscle, the release says. Other forms of SMA treatment include gene therapy, antisense oligonucleotide therapy and small molecule therapy. Muscle targeted therapy seems to work because of the way it promotes muscle growth.

In addition, a Marketing Authorization Application for apitegromab has also been approved and is under review by European Medicines Agency, the release adds.

Pending regulatory approvals, Scholar Rock plans to release apitegromab in the United States later this year, according to the news release. The European launch is planned for 2026.