Shares of Sarepta Therapeutics have struggled for the past year due to concerns about the commercial potential of its gene therapy and broader pipeline. Safety hadn’t been a major worry for investors—

A young person with Duchenne muscular dystrophy died following treatment with the recently approved gene therapy delandistrogene moxeparvovec (Elevidys), Sarepta Therapeutics said in a statement Tuesday.

Elevidys was approved after intense debate at the FDA, as officials and reviewers disagreed over how strong the evidence was and whether it warranted making the drug available for patients facing a fatal disease with few other options.