(Associated Press) – Sarepta Therapeutics said Tuesday that a patient died while taking its closely watched gene therapy for muscular dystrophy, sending company shares plummeting in morning trading.

The young man died of acute liver injury, a known side effect, Sarepta said in a statement. But the company said the “severity” of the patient’s case had not previously been seen with the therapy, called Elevidys. It’s the first known patient death with the therapy, which has been used in more than 800 patients, the company said. (Read More)