One of biotech’s highest fliers, Sarepta Therapeutics, lost more than a third of its market value on Friday after executives said that one of its experimental gene-replacement therapies was linked to the death of a 51-year-old man last month who received the treatment in a clinical trial.

Although Sarepta initially appeared to have avoided the worst possible outcome for Elevidys—market withdrawal—thanks to the gene therapy’s new black box warning, the FDA is signaling stronger misgivings about the approved drug amid a third patient death from an investigational treatment.