A second patient receiving its experimental gene therapy Elevidys has died from liver failure, raising serious questions on the drug’s outlook.

Shares of Sarepta Therapeutics have plunged again after the drugmaker reported a second death in connection with its gene therapy for muscular dystrophy.

Sarepta’s shares crashed 41% in premarket trading Monday morning to $21.01 after the biotech reported a second death from acute liver failure, a known side effect of adeno-associated virus-based gene therapies.