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.

Cambridge-based Sarepta Therapeutics said it was halting shipments of its Duchenne muscular dystrophy gene therapy for patients who can no longer walk, following the death of a second person who received the treatment.