Stealth BioTherapeutics received accelerated FDA approval for elamipretide, a treatment for Barth syndrome, a rare mitochondrial disease, resolving a protracted regulatory process that had included a prior rejection. The approval provides a new option for patients with this ultra-rare condition. The drug’s journey underscores challenges in rare disease drug development and regulatory review. Stealth now moves forward in commercializing a therapy addressing a significant unmet medical need.