WASHINGTON (AP) — The Food and Drug Administration said Friday it will add a new warning and other limitations to a gene therapy for Duchenne’s muscular dystrophy that's been linked to two patient deaths.

The infused therapy from Sarepta Therapeutics will carry a boxed warning — the most serious type — alerting doctors and patients to the risk of potentially fatal liver failure with the treatment, the FDA said in a release.

The one-time therapy, Elevidys, has been under FDA scrutiny since the company reported the first of two deaths of teenage boys in March. Following a second death reported in June, the FDA briefly called for halting all shipments of the drug. But the agency quickly reversed course after facing pushback from patient families and libertarian activists close to President Donald Trump.

Elevidys is the first U.S.-approved gene therapy for Duchenne’s muscular dystrophy, a fatal muscle-wasting disease that affects boys and young men.

In addition to the boxed warning, the FDA is also limiting the drug's approved use to patients who are 4 years old and up and can still walk. Previously the FDA had allowed the drug's use in immobile patients, who generally have more advanced disease.

New labeling will also recommend weekly liver function monitoring for the first three months of treatment, as well as other precautionary steps.

Elevidys is Sarepta's best-selling product and recent headwinds against the drug have weighed heavily on the company and its stock. In July, the Cambridge, Massachusetts-based company announced it would lay off 500 employees.

Sarepta Therapeutics Inc. shares rose 7.7% in trading after the FDA announcement, reflecting improved visibility for investors about the company's outlook.

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