The Food and Drug Administration plans to ask Sarepta Therapeutics to pause shipments of its Elevidys treatment after three deaths were linked to the company’s gene therapies, according to a person familiar with the matter.

Two teenage boys died of acute liver failure in recent months after taking Elevidys. They were being treated for Duchenne muscular dystrophy and weren’t able to walk because of the muscle-wasting disease. Separately, the company said Friday a 51-year-old patient died of acute liver failure last month in an early-stage trial of a gene therapy to treat limb-girdle muscular dystrophy.

The head of the FDA said in an interview with Bloomberg on Friday that the agency will “take a hard look” at Elevidys. Reuters subsequently reported that the agency would ask the company to halt shipments.

The newest patient death occurred in a trial of a gene therapy that uses a similar viral delivery method as Elevidys, meaning it could have safety implications for patients getting the drug that’s on the market.

In an interview, FDA Commissioner Marty Makary said the regulator was examining whether Elevidys should remain available for sale. The FDA was already investigating the two previous patient deaths. Makary made the comment in response to a question from Bloomberg News and didn’t provide any further details.

The regulator is also under pressure for its stance toward Sarepta’s gene therapies. The incident poses one of the first big tests for Vinay Prasad, the new head of the regulator’s gene therapy division. As an academic at UC San Francisco, prior to his current role, he was highly critical of the FDA’s expedited approval process for Sarepta’s gene therapies.

On Wednesday, Sarepta said it had agreed to warn doctors and patients about the risk of liver failure from Elevidys at the request of the FDA. Sarepta executives said the warning label appeared to resolve the FDA’s concerns with using the gene therapy to treat children with Duchenne who can walk. Sarepta said it was still in talks with the FDA about resolving safety concerns with Elevidys for the other portion of the Duchenne market, people who are no longer able to walk.

“On the general question about whether Elevidys as a therapy will remain on the market, the answer is I think pretty clearly yes,” Ingram said Wednesday on the call.

Duchenne muscular dystrophy is a genetic disorder mainly affecting boys that interferes with the production of the protein dystrophin used by muscle cells.

It causes severe muscle weakening and atrophy, with patients needing to use wheelchairs as they get older. Limb-girdle muscular dystroph is a different form of the condition that often weakens muscles around the hips and shoulders.