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.

Following a second patient death, Sarepta is temporarily suspending use of Elevidys in non-ambulatory DMD patients, pending evaluation of an enhanced immunosuppression regimen.

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