FDA Approves Stealth BioTherapeutics’ Forzinity as First Treatment for Barth Syndrome After Rejection and Delay
On September 19, 2025, the FDA granted accelerated approval to Forzinity (elamipretide HCl), making it the first approved therapy for Barth syndrome, a rare and life-limiting genetic disorder that affects about 150 people in the US137.
Barth syndrome is an ultra-rare X-linked genetic condition that weakens heart and skeletal muscles. Forzinity is cleared for use in adults and pediatric patients weighing at least 66 pounds (30 kg)1359.
The approval followed Stealth BioTherapeutics' resubmission of their application, after the FDA previously rejected the drug in May 2025, citing the need for additional safety, manufacturing data, and a post-approval trial plan1268.
Forzinity received accelerated approval based on evidence that it improves muscle strength, with Stealth required to confirm benefits in a post-approval, placebo-controlled trial137.
The approval comes after a protracted process involving initial refusal to review in 2021, delays, staff turnover at FDA, and advocacy from the rare disease community. The dramatic shift in FDA stance allowed a faster decision following resubmission in August 20251.
Stealth will continue working with the FDA to potentially expand access to children under 66 pounds, since many patients with Barth syndrome may not reach this weight threshold13.
This marks the first approval of a mitochondria-targeted therapeutic for any disease, highlighting regulatory flexibility for ultra-rare diseases and the importance of continued innovation in rare disease drug development139.
Sources:
1. https://www.biopharmadive.com/news/fda-approve-barth-syndrome-forzinity-stealth-biotherapeutics-rare-diseases/760710/
2. https://www.biopharmadive.com/news/stealth-fda-resubmit-application-elamipretide-barth-syndrome/757885/
3. https://stealthbt.com/stealth-biotherapeutics-announces-fda-accelerated-approval-of-forzinity-elamipretide-hcl-the-first-therapy-for-progressive-and-life-limiting-ultra-rare-genetic-disease-barth-syndrome/
5. https://www.fiercepharma.com/pharma/fda-greenlights-stealth-bios-injection-1st-treatment-barth-syndrome
6. https://stealthbt.com/stealth-biotherapeutics-announces-fda-acceptance-of-elamipretide-nda-resubmission/
7. https://www.fda.gov/news-events/press-announcements/fda-grants-accelerated-approval-first-treatment-barth-syndrome
8. https://www.prnewswire.com/news-releases/stealth-biotherapeutics-announces-fda-acceptance-of-elamipretide-nda-resubmission-302535179.html