Sarepta Therapeutics Inc said its experimental drug improved walking ability in patients with a rare muscle disorder, sending its shares soaring in premarket trade.

The drug, eteplirsen, significantly improved walking ability in a in a mid-stage trial involving patients with Duchenne Muscular Dystrophy (DMD) -- a genetic disorder that causes severe and progressive muscle loss in boys. There are no approved treatments for the disease.

The study compared two separate doses of the drug, 50mg/kg and 30mg/kg, with a placebo and the higher dose improved walking ability by 89.4 meters.

The improvement was measured by a standard test called the six-minute walk test that checks the cardiac, respiratory, circulatory, and muscular capacity of patients.

Shares of the company jumped 123 percent in premarket trading to $33.40 on Wednesday. They have more than tripled in value through Tuesday after the drug showed improved walking ability according to trial data announced in late-July.

DMD is caused by mutation in a gene that helps produce dystrophin, a vital protein that plays a key role in muscle fiber function.

Eteplirsen showed statistical significance over a placebo by increasing the dystrophin levels to 47 percent.

The biopharmaceutical company said no safety concerns were reported in the study.

Separately, the company said the U.S. Department of Defense (DoD) terminated its contract to develop drugs for treating fever caused by Ebola virus due to funding constraints.

Hemorrhagic fever caused by Ebola is severe and often fatal.