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.

Key Takeaways Sarepta Therapeutics shares sank to their lowest level in nine years Monday after a second patient taking its Elevidys drug died.The patient was being treated for 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.