Rocket Pharma Shares Plunge Over 60% After FDA Halts Gene Therapy Trial

On May 28, Rocket Pharma announced that the U.S. Food and Drug Administration (FDA) had suspended its Phase 2 clinical trial for a gene therapy targeting Danon disease following the death of a patient due to severe complications. The company’s stock fell by more than 60% during intraday trading on Tuesday as a result.

According to the company’s statement, the patient had received treatment in early May and later developed complications associated with capillary leak syndrome. The FDA halted the clinical trial last Friday, prior to the patient's death. Capillary leak syndrome causes fluids to leak from blood vessels into surrounding tissue, leading to swelling and low blood pressure.

The therapy under investigation, RP-A501, is designed to treat Danon disease, a rare genetic disorder that causes heart muscle damage and progressive muscle weakness. Rocket Pharma is currently investigating the cause of death, focusing on a new immunosuppressant recently added to the treatment regimen to improve patient safety. Two patients who received the immunosuppressant showed symptoms of capillary leak syndrome.

CEO Gaurav Shah stated that the company is evaluating whether the new agent might affect immune response in unexpected ways. “Roughly one week after surgery, the patient experienced additional complications. At that time, the condition was stable and we remained cautiously optimistic, with symptoms of capillary leak improving. Unfortunately, over the weekend, the patient developed acute systemic infection, which accelerated the fatal outcome,” Shah said.

Jefferies analyst Andrew Tsai noted that the incident supports the view that serious adverse events in gene therapy remain unpredictable, complicating broader investment in the field. In a separate case in March, a teenager died after receiving Sarepta Therapeutics’ Elevidys gene therapy for muscular dystrophy.

Although Rocket Pharma has not provided a timeline for trial resumption, Shah expressed confidence in continuing the RP-A501 program and stated the company is in active discussions with the FDA and key stakeholders to resume the study as soon as possible.

A report from analysts at William Blair commented: “The stock experienced a sharp drop following Rocket’s announcement… Investors are now concerned about the program’s safety. Nevertheless, we believe that once safety protocols are revised, the trial has potential to proceed.”