FDA Grants Accelerated Approval to Stealth for Barth Syndrom Therapy

Rare Daily Staff

The U.S. Food and Drug Administration granted Stealth BioTherapeutics accelerated approval for Fozainity, the first therapy for the progressive ultra-rare mitochondrial disease Barth syndrome.

The approval is for Fozainity to improve muscle strength in adult and pediatric patients with Barth syndrome weighing at least 30 kilograms.

The decision follows months of discussions with the FDA to resolve the final regulatory milestones following Stealth’s May 2025 receipt of a complete response letter from the FDA, the most recent part of a long and circuitous regulatory path that Stealth had to navigate to win approval.

Barth syndrome is an ultra-rare genetic mitochondrial disease leading to exercise intolerance, muscle weakness, debilitating fatigue, heart failure, recurrent infections, and delayed growth. The disease is associated with reduced life expectancy, with 85 percent of early deaths occurring by age five. Barth syndrome occurs primarily in males and is estimated to affect one in 1,000,000 males worldwide or around 150 individuals in the United States. There are no approved therapies for the treatment of Barth syndrome.

Forzinity is a peptide that targets the inner mitochondrial membrane where it binds to cardiolipin, which plays an essential role in energy conversion within cells. It has received Orphan Drug, Fast Track, Priority Review, and Rare Pediatric designations from the FDA and Orphan Drug designation from the European Medicines Agency for the treatment of Barth syndrome.

Forzinity received Orphan Drug, Fast Track, Priority Review, and Rare Pediatric designations from the FDA and Orphan Drug Designation from the European Medicines Agency for the treatment of Barth syndrome.

The approval of Forzinity is supported by the efficacy and safety data from the TAZPOWER clinical trial. During the open-label portion of the TAZPOWER trial, knee extensor muscle strength improved from study baseline. The most common adverse reactions were injection site reactions, which can be treated with oral antihistamines or topical corticosteroids. Continued approval for this indication may be contingent upon verification of clinical benefit in a confirmatory trial.

In connection with the approval, Stealth has been granted a Rare Pediatric Disease Priority Review Voucher from the FDA.

“The approval of Forzinity, the first treatment option for Barth syndrome and the first approved mitochondria-targeted therapeutic, is a pivotal victory for the Barth syndrome community and offers hope for expedited regulatory attention to other ultra-rare diseases,” said Reenie McCarthy, Stealth’s CEO.

She said the company plans to provide expanded access to children weighing less than 30 kilograms who are currently receiving treatment or require emergency access, while it works with the agency to generate data needed to expand the indication to include these children.

Reenie McCarthy, StealthBio CEO