Amid Controversy, Duchenne Muscular Dystrophy Drug Is Approved By FDA

A new drug developed to treat the rare disease Duchenne muscular dystrophy, has been approved by the US Food and Drug Administration (FDA). Benefitting from an accelerated approval, Sarepta Therapeutics’ Exondys 51 is the first drug to become available to patients with the disease.

As suggested by its name, Exondys 51 was developed for Duchenne muscular dystrophy patients with a mutation in the dystrophin gene on exon 51. The drug can encourage cellular machinery to skip exon 51, thereby producing a more functional protein.* This mutation is found in approximately 13 percent of the Duchenne muscular dystrophy patient population.

“Patients with a particular type of Duchenne muscular dystrophy will now have access to an approved treatment for this rare and devastating disease,” said Dr. Janet Woodcock, director of the FDA’s Center for Drug Evaluation and Research. “In rare diseases, new drug development is especially challenging due to the small numbers of people affected by each disease and the lack of medical understanding of many disorders. Accelerated approval makes this drug available to patients based on initial data, but we eagerly await learning more about the efficacy of this drug through a confirmatory clinical trial that the company must conduct after approval.”

Potential approval of the drug was debated for months, with some concerned that the drugmaker lacked evidence that Exondys 51 had a significant impact on patients. Earlier this year, FDA medical staffers raised a number of concerns about the drug, including the fact that it was only tested in a small 12-patient clinical trial.

While the FDA decided to approve the drug in spite of these issues, they are requiring Sarepta to conduct an additional randomized controlled trial to reconfirm the patient benefits of the drug over a two-year period. If that trial fails to show a significant improvement in motor functions in Duchenne muscular dystrophy patients, the FDA could rescind Exondys 51’s approval.

Duchenne muscular dystrophy is a rare genetic disease caused by a lack of the protein responsible for maintaining muscle cell integrity, known as dystrophin. This deficiency results in muscle deterioration and weakness which first begins to manifest between three and five years of age, with progressive worsening over time.

*Editor’s Note: Sentence was rewritten to clarify action of Exondys 51.