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# Gene Therapy Trial on Hold After Death
- URL: https://www.fdaweb.com/gene-therapy-trial-on-hold-after-death/
- Published: 2025-05-27T12:00:00.000Z
- Updated: 2026-09-14T15:12:42.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5159250

FDA has placed a clinical hold on a Rocket Pharmaceuticals Phase 2 pivotal trial for RP-A501, an investigational gene therapy for Danon disease, following the death of a participant who experienced serious complications during the study. The patient developed a serious adverse event (SAE)related to capillary leak syndrome, the company says, adding that despite medical intervention, the patient later died due to an acute systemic infection.

Rocket says it is currently conducting a comprehensive root cause analysis, and early assessments suggest the SAE may be linked to the recent introduction of a new immune suppression agent added to the pre-treatment regimen. This agent was designed to counteract complement activation — an immune system response observed in previous patients — and was specific to the RP-A501 program, it adds.

RP-A501 is described as a one-time gene therapy candidate that uses an AAV9 vector to deliver a healthy version of the LAMP2B gene, which is mutated in Danon disease, a rare and often fatal inherited disorder that primarily affects the heart and is estimated to impact 15,000 to 30,000 people across the U.S. and Europe. Currently, heart transplantation is the only available treatment.