PTC Therapeutics withdrew its U.S. filing for Translarna (ataluren) after the FDA signaled the submitted data were unlikely to meet the agency’s standard for substantial evidence of effectiveness in nonsense-mutation Duchenne muscular dystrophy. PTC said it could not reconcile differing interpretations of trial endpoints with regulators and pulled the application. Regulators cited uncertainties about the relationship between the blood-based biomarker used in trials and meaningful clinical benefit. The withdrawal follows a European regulatory setback and marks another high-profile rare-disease regulatory disappointment, underscoring the tightened evidentiary expectations for surrogate endpoints in progressive neuromuscular disorders. Clarification: nonsense-mutation DMD is a subset of Duchenne muscular dystrophy caused by specific mutations that prematurely truncate dystrophin production.