FDA expands approval of first gene therapy for rare form of muscular dystrophy

(CNN) — The US Food and Drug Administration has given the green light for the first gene therapy that treats a rare form of muscular dystrophy to be used in most people who have the disease and a certain genetic mutation.

Last year, the drug – Elevidys, from the biotech company Sarepta Therapeutics – was approved to treat only children ages 4 and 5 with Duchenne muscular dystrophy, one of the most severe forms of inherited muscular dystrophies, who have a confirmed mutation in a gene called DMD that is associated with muscle strength.

The FDA announced Thursday that it had given traditional approval for Elevidys for ambulatory people 4 and older with a confirmed mutation in the DMD gene and accelerated approval for non-ambulatory people 4 and older with this mutation. There’s not enough data on safety to support its use in children under 4, the agency says.

Elevidys, given as a one-time intravenous infusion, costs about $3.2 million per patient, making it among the most expensive drugs in the world. Although eye-popping, such a price tag isn’t out of step with other one-time gene therapies, which have topped $3 million to 4 million per patient in recent years.

Elevidys was previously approved under the FDA’s accelerated approval pathway, which clears medicines for diseases where they’re urgently needed based on data suggesting that they’re likely to confer clinical benefits. The drug has been closely monitored since that approval, and in October, Sarepta Therapeutics released results from a confirmatory trial showing that the therapy missed its primary goal – a measure of how well kids can move – but was successful on a number of secondary measures.

The approval addressed “an urgent unmet medical need and is an important advancement in the treatment of Duchenne muscular dystrophy, a devastating condition with limited treatment options, that leads to a progressive deterioration of an individual’s health over time,” Dr. Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a news release at the time.

It was the first time a therapy of this nature – a one-time treatment that delivers a working copy of a gene to make up for one that leads to disease – had been cleared under the accelerated approval framework. The move came after emotional testimonials from families at an FDA advisory committee meeting.

Duchenne muscular dystrophy causes progressive muscle weakness that can rob children of their ability to walk by the time they’re teenagers, and many don’t live well into their 30s. It primarily affects boys because of the way it’s inherited, affecting an estimated 1 in 3,300 boys.

The Muscular Dystrophy Association trusts the decision of the FDA, which weighs the risks and benefits of the drug, said Dr. Sharon Hesterlee, chief researcher at the association.

“Ultimately, what we want is what’s best for our patient community – and that’s balancing that risk-benefit ratio appropriately,” she said.

Potential risks of Elevidys include increases in certain liver enzyme levels and acute serious liver injury. The most common side effects of the drug include vomiting, nausea, increased liver function tests and fever.

Yet a major benefit is that the gene therapy provides another option for people with Duchenne muscular dystrophy, and it’s administered just once.

There is no cure for Duchenne muscular dystrophy, and outside of Elevidys, treatments are limited. Other approaches may include steroid medications, certain drugs that change how the muscle cells “read” the mutated gene, physical therapy or surgery to correct spinal curvature, Hesterlee said.

“Right now, the main standard of care for Duchenne is corticosteroids, like prednisone, although there are some newer drugs available. These kids are still often on chronic doses of steroids for many, many years,” she said, adding that the side effects of corticosteroids – such as weight gain, behavioral issues and increased risk of bone breakage – are not ideal.

Duchenne muscular dystrophy can be difficult to treat, she said, and having more treatment options that are proven to be effective remains important.

“Muscle makes up a significant amount of your body mass. So when you have a disease like this, it’s really impacting a lot of tissue. So anything you do, you’re looking at trying to bring back or stop a disease process that’s really throughout the body, and it’s a disease that’s progressive, so you lose more and more muscle over time,” Hesterlee said.

“That’s made it pretty challenging, but we’ve certainly learned a lot,” she said. “You can’t overlook the fact that these boys are living so much longer and doing so much better. Even 20 years ago, they were dying in their teens, and many of them are now living into their 30s. They’re going to college; they have girlfriends; some of them have gotten married. These are things that weren’t happening years ago. So we’ve made a tremendous amount of progress.”

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CNN’s Meg Tirrell contributed to this report.