CAMBRIDGE — A biotech firestorm is brewing after Cambridge-based Sarepta Therapeutics flat-out refused a request from the FDA to halt shipments of its flagship gene therapy — even after a third patient died from complications tied to the treatment.

The therapy, called Elevidys, was billed as a breakthrough for Duchenne muscular dystrophy, a rare and devastating genetic disease that primarily affects boys. But with three deaths now linked to liver injury, and federal regulators raising the alarm, Sarepta isn’t pulling the plug. It’s doubling down.

While the FDA typically relies on voluntary cooperation, Sarepta's refusal to comply is virtually unprecedented. The agency confirmed it asked the company to suspend sales of Elevidys — but Sarepta said no.

“We believe in access to drugs for unmet medical needs but are not afraid to take immediate action when a serious safety signal emerges,” said FDA Commissioner Marty Makary.

The move places Sarepta at the center of a growing storm around experimental gene therapies — a field that surged during the COVID-19 pandemic and promised to revolutionize medicine. But as the hype fades, real-world complications — and real-world casualties — are forcing a reckoning over how fast is too fast when it comes to approval.

This week, Sarepta laid off 500 workers and said it would add a bold warning to Elevidys’ label. But it did not disclose a third death — a 51-year-old man in a separate muscular dystrophy trial — until Friday, weeks after informing the FDA. All three fatalities were tied to liver injury, a known risk.

Two of the deaths involved teenage boys taking Elevidys. Sarepta quietly paused shipments for older patients in June. But the company says it will continue to supply the drug to younger, ambulatory patients, claiming its internal review showed no new or changed safety signals.

Critics say this is part of a pattern. Sarepta has marketed multiple drugs for Duchenne’s without completing confirmatory studies. None have been definitively proven to work. And Elevidys itself was approved under the FDA’s accelerated approval pathway in 2023 — despite pushback from internal FDA scientists who questioned its effectiveness.

The full approval came later, expanding use to older patients, even as safety red flags were beginning to emerge.

Now, with patients dead, regulators frustrated, and public trust wavering, Sarepta is digging in.

But the scandal raises a deeper question: How many risks are we willing to take with gene therapy — and how much faith is left in the system meant to keep it safe?