Rocket Pharmaceuticals Inc ( RCKT ) announced an update Tuesday related to RP-A501, its investigational gene therapy for Danon disease, a rare X-linked dominant genetic disorder that manifests with the clinical triad of cardiomyopathy (stiff heart muscles), skeletal myopathy (weakness) and intellectual disability.

A patient participating in the Phase 2 pivotal trial of RP-A501 experienced an unexpected Serious Adverse Event (SAE). The patient passed away after an acute systemic infection.

Also Read: Rocket Pharma’s Gene Therapy Shows Promise in ACM Patients, Says Analyst

The SAE involved clinical complications related to capillary leak syndrome, where fluid and proteins leak out of tiny blood vessels (capillaries) and into the surrounding tissues.

Rocket is conducting a comprehensive root cause analysis. It remains in active dialogue with the U.S. Food and Drug Administration (FDA) and other key stakeholders. The current focus is on the recent introduction of a novel immune suppression agent to the pre-treatment regimen implemented to mitigate complement activation observed in some patients.

This novel agent was specific to the AAV9-Danon program.

Upon learning of the initial event, Rocket voluntarily paused further dosing in the study. The FDA placed a clinical hold on the trial for further evaluation.

While the clinical hold remains in place, the company is unable to provide guidance on the anticipated completion date of the Phase 2 trial.

As of March 31, 2025, Rocket had cash, cash equivalents, and investments of $318.2 million. The company is prioritizing investment in its AAV platform while assessing ways to optimize value for the rest of the pipeline, which will reduce overall cash spent.

Rocket now expects its existing resources to be sufficient to fund operations into 2027, excluding any potential proceeds from the sale of Priority Review Vouchers that could follow the approval of therapies from the hematology portfolio.

In November 2024, Rocket Pharmaceuticals ( RCKT ) presented long-term safety and efficacy results from the Phase 1 study of RP-A501 in male patients with Danon disease.

Danon disease is caused by mutations in the LAMP2 gene, which contains instructions for the production of an enzyme called lysosomal-associated membrane protein-2 (LAMP-2). The data showed that RP-A501 was generally well tolerated.

All evaluable Danon disease patients demonstrated LAMP2 protein expression at 12 months (sustained up to 60 months) and reduction of left ventricular (LV) mass index by ≥10% at 12 months (sustained up to 54 months) after treatment.

Price Action: At the last check on Tuesday, RCKT stock was down 64.3% to $2.24 during the premarket session.

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