Rocket Pharmaceuticals AAV Gene Therapy for Danon Disease Receives FDA Clearance to Resume Clinical Trial

WASHINGTON D.C., August 20, 2025 – The U.S. Food and Drug Administration (FDA) has lifted a clinical hold on a Phase II trial for RP-A501, an investigational AAV-based gene therapy for Danon disease, Rocket Pharmaceuticals announced today. The decision comes after a patient died in late May following treatment, which prompted the hold.

The trial can now proceed using a recalibrated, lower dose of the AAV gene therapy. The company has also adjusted the immunomodulatory regimen patients receive, opting for one similar to a regimen successfully used in a pediatric group from an earlier Phase I trial. A previously used C3 complement inhibitor has been removed from the regimen.

Analysts and experts were encouraged by the FDA’s swift action, noting that the hold was lifted in under three months—a shorter timeframe than is typical for such events in the gene therapy space. This speed, according to analysts, may signal the FDA’s flexibility and understanding of the high unmet medical need for Danon disease.

Danon disease is a rare, X-linked genetic disorder caused by a mutation in the LAMP2 gene, which leads to progressive heart failure. The RP-A501 gene therapy is designed to use an AAV vector to deliver a functional copy of the LAMP2 gene to heart muscle cells, aiming to treat the underlying cause of the disease.