Federal Food and Drug Administration officials have said no to an experimental drug to treat Duchenne muscular dystrophy, saying it didn’t meet agency standards for effectiveness.

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Federal regulators Thursday declined to approve an experimental drug to treat patients with a deadly muscle-wasting disease, including a Maple Valley boy whose family was counting on it.

The Food and Drug Administration (FDA) turned down the application for Kyndrisa, generically known as drisapersen, to treat Duchenne muscular dystrophy, a genetic disorder that primarily affects boys.

The drug did not meet “substantial evidence of effectiveness,” the agency told drugmaker BioMarin Pharmaceuticals, in a formal response. It followed a tepid review by an FDA subcommittee in November.

The decision hit hard at the home of Gavin Carlone, 9, whose family had lobbied the agency and media in hopes of gaining approval. Tonya Carlone, Gavin’s mother, said the drug has allowed the third-grader to walk, ride bikes and play soccer with friends, despite being diagnosed as a toddler with the rare disorder.

“It’s pretty devastating news,” she said. “I totally disagree with the FDA’s findings.”

Without the drug, Gavin almost certainly will lose function, his mother said. Duchenne prevents formation of a crucial muscle protein, putting most patients in wheelchairs by age 12 and eventually leading to death in young adulthood.

Gavin likely won’t be pulled off the drug immediately, but the future is uncertain, his mother said. BioMarin officials said in a news release the firm would continue to work with the FDA on the drug application.

The decision comes days before an FDA panel is to review an application from drugmaker Sarepta Therapeutics, for another Duchenne treatment, eteplirsen. Both drisapersen and eteplirsen are so-called exon-skipping drugs that bypass the genetic mutation, allowing formation of the protein.

If approved, such drugs could help about 13 percent of all patients with Duchenne, which affects about 1 in every 3,000 to 5,000 male children.