Sarepta Therapeutics said a second patient had died after receiving its $3.2 million gene therapy to treat Duchenne 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.

Shares of Sarepta Therapeutics closed down as much as 42% to hit a nine-year low of $18.30 on Monday after a second death of a male teenage patient who had received its gene therapy, Elevidys, raising doubts on the safety and future demand for the treatment.