The Food and Drug Administration has rejected a drug that would have become the first treatment for Duchenne muscular dystrophy, a rare and ultimately fatal condition that affects about one in every 3,500 boys.

BioMarin Pharmaceutical, the company behind the drug known as drisapersen, said in a statement that agency officials “concluded that the standard of substantial evidence of effectiveness has not been met” and that the treatment "is not ready for approval in its present form."

The decision was not unexpected. Ahead of an FDA advisory hearing last fall, agency staffers raised serious concerns about the drug's “contradictory” effectiveness data, as well as “life-threatening” safety risks such as severe kidney damage and low blood platelet counts. Members of an outside advisory panel subsequently raised similar issues.

BioMarin said Thursday that it will continue clinical trials of the drug and "will work with the FDA to determine the appropriate next steps regarding this application." The drug remains under review by regulators in Europe.

"We are disappointed that the FDA did not approve drisapersen, given the significant benefit that many Duchenne boys experienced when they were on an early and consistent treatment protocol of the drug," Debra Miller, chief executive of CureDuchenne said in a statement. The nonprofit group helped fund the drug's development. "Our fight to cure Duchenne muscular dystrophy goes on."

[‘How do you tell a kid he’s not going to grow up?’]

Later this month, the advisory panel is scheduled to consider approval of another Duchenne drug, eteplirsen, made by Sarepta Therapeutics. Families with boys on that drug -- or who want access to the drug -- have petitioned the White House, visited lawmakers on Capitol Hill and made their case to top FDA officials that their children's unmet medical need warrants approval based on the existing clinical evidence. Despite some reservations expressed by federal regulators about eteplirsen, parents and advocates in the Duchenne community have made clear they are willing to accept a high level of risk in exchange for the potential benefits, particularly when the alternative is death.

Duchenne is caused by a mutation in the gene responsible for producing dystrophin, an essential protein involved in muscle function. Without it, even routine activities can damage muscles, causing them to die and be replaced by fat and other tissue. Boys typically receive a diagnosis by age 6, and the disease’s steady progression leaves many of them immobile by the time they are teens. It eventually affects the heart and respiratory muscles, making breathing difficult. Most patients die in their 20s or 30s.

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