The U.S. Food and Drug Administration (FDA) has approved the first drug for treating patients with Duchenne muscular dystrophy. Patients who have this condition are typically boys who lose their ability to walk by 12 years old and are likely to suffer from heart or respiratory failure by the time they reach their 20s.

The approval went against the recommendation of experts who did not find enough evidence that the drug was effective. The agency's decision, however, showed the growing power of patients and advocates over evaluation of drugs.

It is estimated that between 9,000 and 12,000 Americans have Duchenne muscular dystrophy. Those who have this condition make little or no dystrophin, a protein that serves as a shock absorber to protect muscles from deterioration. Patients typically die young so the agency's decision was welcome news to families and patients who battle with the disease.

"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," said Janet Woodcock, director of FDA's Center for Drug Evaluation and Research.

The newly approved drug eteplirsen can be used by only about 13 percent of the patients. Other drugs are currently being developed for patients who have different mutations.

The drug is supposed to work by partly correcting genetic defect so the muscle cells can produce a somewhat functional form of dystrophin.

Eteplirsen maker Sarepta said that the cost of the drug would be about $300,000 per patient per year.

The decision on the drug was delayed for months and the approval was so controversial it prompted a dispute among FDA employees. While the decision delighted the advocates of the drug who actively lobbied for its approval for years, drug policy experts are worried about FDA's decision.

Earlier this year, an FDA panel of experts said that Sarepta was not able to show significant evidence that its drug can boost the production of dystrophin to a level that can be clinically beneficial to patients. The committee also did not find substantial evidence that the drug is an effective treatment for people who have the degenerative disease.

"The agency has set a dangerous precedent," said National Center for Health Research president Diana Zuckerman. "To prove something works, you have to compare it to something else — a placebo or a treatment. They didn't do that."