The U.S. Food and Drug Administration announced Monday its approval of a drug that treats patients with Duchenne Muscular Dystrophy (DMD).

The drug, Exondys 51 (eteplirsen), is to be used particularly for those with a “confirmed mutation of the dystrophin gene amenable to exon 51 skipping,” a condition said to affect 13 percent of all DMD patients. It is the first drug treatment approved by the FDA to treat the disease.

“Patients with a particular type of Duchenne muscular dystrophy will now have access to an approved treatment for this rare and devastating disease,” Janet Woodcock, director of the agency’s Center for Drug Evaluation and Research, said in a statement.

The agency gave the green light for Exondys 51 despite recommendations from its advisers not to do so.

Although doctors and patients provided testimonies on how the drug was able to allow boys to walk longer, effectively delaying the need for a wheelchair, the agency’s advisers said the drug failed to meet FDA requirements. Additionally, the study presented by the drug’s manufacturer involved only 12 patients.

Woodcock explained drug approval for diseases that affect only a small number of people can be challenging.

“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,” she said.

DMD is a genetic disorder that causes the muscles to weaken and degenerate over time. Symptoms can appear as early as three years of age. It often affects boys, although there are rare cases of girls with DMD.

As the child grows, the muscles continue to weaken until the child can no longer perform normal activities. Upon reaching 12 or early teens, the patient will begin to require a wheelchair. Eventually, heart and respiratory muscles also start to weaken. Patients often die early, surviving up to their 20s or 30s.

One out of 3,600 infants worldwide have DMD.

Murdoch University researcher Steve Wilton, one of the drug developers, said the drug allowed patients to walk “past their loss of ambulation date.”

"These sick kids were on the edge of a cliff, they were about the lose the ability to walk,” he remarked.

With the recent approval of Exondys 51, many families whose lives have been affected by the disease could not help but feel a surge of hope. Fiona and Rob Ball, parents of six-year-old Maddox, are among them.

On the outside, Maddox appears to be functioning normally like other kids, but his movements are already showing telltale signs of the disease. For instance, he displays a slight limp when he runs. Because of this, he cannot run as fast as the other kids.

Maddox would jokingly say he has “naughty muscles.”

"He calls them naughty muscles and he just finds it hard to keep up with everybody else," Fiona said.

Although Exondys 51 does not cover Maddox’s genetic mutation, Fiona is hopeful that it would open up new possibilities for DMD treatment.

"It would completely change our whole lives and change Maddox's life," she said.