Shares of Sarepta Therapeutics soared about 15 percent in premarket trading on Wednesday after the company reported positive results from a clinical trial of an experimental medicine for Duchenne muscular dystrophy.

The drug would be Sarepta’s second to treat the rare, genetic disease, which causes muscle wasting and can be fatal before patients turn 30. The treatment targets a genetic mutation affecting about 8 percent of patients with DMD. Sarepta’s first drug, approved by the FDA last year, treats a mutation affecting about 13 percent.

The results, announced before Wall Street’s open bell, showed the medicine, called golodirsen, increased production of the protein dystrophin to 1.02 percent of normal levels from about 0.095 percent without the drug. Analysts said those results were higher than expected.

Sarepta said the underlying cause of DMD is a mutation in the gene for dystrophin, which is an essential protein involved in muscle fiber function. The study, conducted in Europe, involved 25 boys with confirmed deletions of the DMD gene amenable to skipping exon 53. Exons are part of the DNA code.

“These data … further validate the broad application of our exon-skipping platform and aligns with our strategic imperative to expand and improve the treatment choices for the majority of patients with DMD,” Sarepta CEO Doug Ingram said in a statement.

Sarepta focuses on the discovery and development of precision genetic medicines to treat rare neuromuscular diseases.