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Rocket Pharmaceuticals, Inc. (NASDAQ: RCKT) has received FDA support to continue testing an experimental treatment for Danon disease, a rare inherited condition that can seriously damage the heart.
The company said the FDA agreed with its plans for the next stage of a Phase 2 study of RP-A501. The decision means Rocket can continue enrolling and treating patients under a revised study plan. It also gives the company a clearer idea of how many patients it needs and what results it will use to judge the treatment.
Rocket said three patients have already received the revised dose. Those patients will count toward the 12-person study group, leaving nine more patients to enroll and treat. The company expects to complete dosing of the remaining patients by mid 2027.
Danon disease is caused by a change in a gene called LAMP2. That gene helps cells clear out damaged material and keep themselves working properly. When it does not function as it should, the heart muscle can become unusually thick and eventually have difficulty pumping blood.
The disease is especially serious in boys and young men. It can also affect muscles and the brain. Because Danon disease is rare, patients have limited treatment options, and doctors often focus on managing the heart problems rather than correcting the cause of the disease.
RP-A501 is designed to deliver a working version of the LAMP2B gene to heart cells. The goal is to help those cells produce the missing protein. Earlier research involving the treatment found evidence that it reached the heart and produced LAMP2 protein, although the program has also faced safety challenges that led to changes in the study design.
The three patients treated under the revised plan completed at least four weeks of follow up and were discharged after the required monitoring period. Rocket said none showed clinical or laboratory evidence of two serious complications that the company was watching for, thrombotic microangiopathy and capillary leak syndrome.
Those medical terms describe potentially dangerous problems involving blood vessels, blood flow and fluid movement in the body. Their absence in the initial group does not prove that the treatment is safe, but it gave the FDA enough information to support continued dosing under the modified protocol.
The revised plan uses a recalibrated dose of 3.8 x 1013 genome copies per kilogram. It also includes additional safety checks and an immune management program using rituximab, sirolimus and corticosteroids.
Rocket and the FDA have agreed to assess the patients after 12 months using two main measures. Researchers will check whether heart tissue is producing LAMP2 protein and whether the size of the heart’s main pumping chamber has fallen by at least 10% from the starting measurement.
These measurements are not the same as proving that patients will live longer or feel better. However, the FDA allows some treatments for serious conditions to move through its accelerated approval process when a measurable biological result is considered reasonably likely to predict a meaningful benefit. Any approval would still depend on the total evidence from the study.
Rocket plans to discuss the program during a virtual investor webinar on October 6, 2026, at 4:30 p.m. Eastern Time. The update is expected to cover the early safety information, the remaining enrollment schedule and the next steps for RP-A501.
