(Reuters) - PTC Therapeutics Inc’s experimental drug to treat Duchenne muscular dystrophy, a devastating degenerative disease that mostly affects young boys, may work but the company will need to do more work to prove it, an advisory panel to the U.S. Food and Drug Administration concluded on Thursday.

FILE PHOTO: A view shows the U.S. Food and Drug Administration (FDA) headquarters in Silver Spring, Maryland August 14, 2012. REUTERS/Jason Reed/File Photo

The panel’s vote reduces the chance the drug will be approved soon since the FDA generally follows the advice of its advisors. Even so, the vote could have been worse for PTC. The panel could have rejected the drug outright, which in turn could have imperiled European sales of the product.

In Europe the drug is approved on a conditional basis, meaning approval must be renewed every year. It could win full European approval if data definitively proving effectiveness is submitted during the conditional period.

FDA scientists argued strongly that the company had failed to prove that the drug works. More fundamentally, said Dr. Billy Dunn, director of neurology products at the FDA, the company had sliced and diced data to try to extract a positive result, making the entire data set untrustworthy.

“We are not arguing about the numbers,” Dunn said. “Our concern is much more fundamental and concerns the basis of the scientific method.”

Panelists tended to agree. Ten out of 11 voted that the data were inconclusive.

Dr. Aaron Kesselheim, Associate Professor of Medicine at Harvard Medical School, said he was concerned about the possibility that the way the data was analyzed could be misleading.

Duchenne muscular dystrophy (DMD) starts in childhood and mainly affects males. More than 90 percent of patients become wheelchair-bound by the age of 15. There is no cure.

PTC argued that the FDA has the flexibility to approve the drug, even though it failed to meet the goal of multiple clinical trials. It noted that ataluren increased the production of dystrophin, a protein needed for muscle development.

Earlier this year Dr. Janet Woodcock, head of the FDA’s pharmaceuticals division, ordered the approval of a Duchenne treatment made by Sarepta Therapeutics Inc even though the advisory panel and the agency’s own scientists recommended against approval, saying there was almost no evidence the drug worked.

FDA scientists warned that approval for Sarepta’s drug, Exondys 51, or eteplirsen, would lower the bar for approval of other drugs.

Dr. Joe McIntosh, PTC’s head of clinical development, insisted that “the totality of the data” showed ataluren can slow the loss of muscle function. He said the drug produced an increase in dystrophin and that “FDA has approved another therapy for Duchenne based solely on dystrophin production.”

Ataluren is designed for patients with DMD caused by a mutation in the DMD gene known as a nonsense mutation, which prevents the body from producing a key protein needed for muscle development.

The FDA in 2016 refused to review ataluren because of its failure in clinical trials. PTC proceeded to file its application “over protest” under a rarely used procedural move that allows a company to have its application reviewed when there is a disagreement with regulators over the application’s acceptability.

If approved the drug would be marketed under the name Translarna. PTC’s shares we halted for the all-day meeting. They closed on Wednesday at $17.46.