Shares of Sarepta Therapeutics Inc. have lost more than 26% this week, heading for their worst such performance in over a year, after the company disclosed the death of a Duchenne muscular dystrophy (DMD) patient treated with its Elevidys drug.

Sarepta Therapeutics said a patient taking its treatment for Duchenne muscular dystrophy has died from acute liver failure. The pharmaceutical firm said that "acute liver injury is a known possible side effect of Elevidys.

Sarepta Therapeutics said Tuesday that a patient died while taking its closely watched gene therapy for muscular dystrophy, sending company shares plummeting more than 25%. The young man died of acute liver injury,