FDA delays decision on Sarepta’s controversial gene therapy for muscular dystrophy

The agency was scheduled to rule on the Cambridge company’s medicine by Monday, but will now wait until June 22.

Sarepta Therapeutics is based in Cambridge.Ruby Wallau

The Food and Drug Administration is delaying by one month its long-awaited decision on whether to approve a gene therapy for a deadly inherited muscle-wasting disease that afflicts more than 10,000 boys and young men nationwide, according to the Cambridge biotech that developed the medicine.

Sarepta Therapeutics said Wednesday that after discussions with the FDA, the agency has postponed until June 22 its deadline for deciding whether to give fast-track approval to the treatment for Duchenne muscular dystrophy. Regulators had planned to announce a decision by Monday.

The FDA also informed Sarepta that “it is working toward potentially granting an accelerated approval” of the gene therapy “initially for use in Duchenne patients ages 4-5 years,” according to a news release by the drug firm.

Sarepta had requested fast-track approval for all Duchenne patients who could still walk, which would have included most under the age of 10 and even some teenagers.

The decision to narrow the group of patients for whom the drug might be approved wouldn’t come as a complete surprise. FDA staffers told a panel of outside scientific advisers on May 12 that Sarepta’s experimental single-dose gene therapy showed better results among younger boys than older ones in a randomized clinical trial.

The staffers found “no statistically significant difference” between the gene therapy and a placebo for all but the youngest patients in the clinical data they reviewed, Mike Singer, a clinical reviewer to the FDA Center for Biologics Evaluation and Research, told the panel.

The possibility that the FDA could clear the treatment has buoyed families of boys with Duchenne muscular dystrophy. It has also drawn criticism from some scientists and health research experts who say the FDA is loosening its standards.

Detractors say greenlighting the drug would be a misuse of the 31-year-old accelerated approval program. That process enables regulators to speed up approval for medicines targeting serious unmet medical needs if they show promise in clinical trials.

But the advisory panel narrowly recommended approval in an 8-to-6 vote, with some members saying they were swayed by wrenching testimony from parents who shared videos of their boys playing sports after having received the gene therapy in the clinical trial.

Dr. Anthony Amato, a Harvard professor of neurology who has treated Duchenne for decades and voted with the majority, called the videos part of the “compelling evidence this was effective” for some patients.

Robert Weisman of the Globe staff contributed to this report.