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.

Sarepta Therapeutics shares sank to their lowest level in nine years Monday after a second patient taking its Elevidys drug died.

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