CAMBRIDGE, Mass. ( TheStreet) -- Sarepta Therapeutics ( SRPT) said 48 weeks of treatment with an experimental drug eteplirsen produced significant amounts of a critical protein needed for muscle function and helped boys with a form of muscular dystrophy improve their walking ability.

The results from the mid-stage study are not only positive but medically groundbreaking because never before has a drug been shown to reverse the progressive decline in muscle function that is a hallmark of Duchenne muscular dystrophy.

Some of the DMD patients treated with eteplirsen increased the distance they were able to walk in six minutes by 21 meters over the course of the study.

Sarepta intends to meet with the U.S. Food and Drug Administration about seeking early approval for eteplirsen, the company said.

Shares of Sarepta more than doubled in value after Wednesday's announcement, up 115% to $32.50. The stock was already up more than 300% in value since July when positive, interim results from the eteplirsen study were announced.

After 48 weeks of treatment, four DMD patients treated with a 50 mg dose of eteplirsen demonstrated a 21-meter increase in the six-minute walk test from baseline. By comparison, patients who received placebo for 24 weeks followed by 24 weeks of eteplirsen showed a decline of 68.4 meters from baseline in the six-minute walk test. The overall benefit of 89.4 meters was statistically significant.

There was no statistically significant difference in walking distance between patients treated with 30 mg of eteplirsen and the placebo/delayed treatment patients.

Along with the improved walking ability, eteplirsen also caused an increase in levels of dystrophin, a key protein that supports muscle function. Eteplirsen at both doses resulted in a statistically significant increase in dystrophin to 47% of normal. The placebo/delayed treatment group of patients saw a smaller increase of dystrophin to 38% of normal.

Dystrophin is a protein that plays key role in muscle function and repair. The genetic inability to make dystrophin is what causes muscular dystrophy. Eteplirsen is designed to "skip over" the section of damaged gene in DMD patients and therefore restore the gene's ability to produce partially functioning dystrophin.

-- Reported by Adam Feuerstein in Boston.

Adam Feuerstein writes regularly for TheStreet. In keeping with company editorial policy, he doesn't own or short individual stocks, although he owns stock in TheStreet. He also doesn't invest in hedge funds or other private investment partnerships. Feuerstein appreciates your feedback; click here to send him an email.

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