FDA Halts Rocket Pharmaceuticals Gene Therapy Trial Following Patient Death

The U.S. Food and Drug Administration (FDA) has paused a mid-stage clinical trial by Rocket Pharmaceuticals after a patient receiving its experimental gene therapy for Danon disease suffered severe complications and later died.

The trial, which was testing RP-A501, aimed to treat Danon disease—a rare, inherited condition that affects the heart and muscles. Rocket Pharmaceuticals confirmed that the patient developed capillary leak syndrome, a serious condition where fluids leak from blood vessels into surrounding tissues, causing dangerous drops in blood pressure. The patient ultimately died due to a severe systemic infection.

In light of the incident, Rocket voluntarily suspended further dosing, and the FDA issued an official clinical hold on May 23 to allow for a full investigation.

The company is now working closely with the FDA, medical experts, and an independent safety board to determine the exact cause of the complication. Investigators are also reviewing whether a newly introduced immune-suppressing drug used before treatment may have contributed to the adverse event.

No timeline has been given for when the trial might resume. Rocket’s stock dropped sharply following the announcement.

This development underscores the complexity and high stakes of advancing gene therapy treatments, particularly for rare diseases like Danon disease, where therapeutic options remain limited.