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.

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.

Elevidys was approved after intense debate at the FDA, as officials and reviewers disagreed over how strong the evidence was and whether it warranted making the drug available for patients facing a fatal disease with few other options.