Stealth BioTherapeutics has resubmitted its drug application for an ultra-rare Barth syndrome therapy following an FDA rejection earlier this year. The company has struggled to align with the agency on clinical data requirements due to the small patient population. The drug is currently available via expanded access, and company officials express hope for a timely regulatory decision to prevent potential closure. Stealth’s ongoing regulatory interactions highlight challenges faced by ultra-rare disease developers seeking approval under demanding evidentiary standards.