BOTHELL, Wash. (


) --

Sarepta Therapeutics

(SRPT) - Get Report

unveiled the first data demonstrating that an experimental "genetic fix" can significantly improve the walking performance of patients with muscular dystrophy.

Results from the small study are still preliminary but the Sarepta drug, known as eteplirsen, is a potential medical breakthrough because it may be the first to treat the underlying cause of Duchenne muscular dystrophy (DMD), a rare genetic disease for which there is no effective treatment.

Last April, Sarepta presented data showing that eteplirsen

increases levels of a key protein involved in muscle function

but Tuesday's results were the first to show a more tangible, or real-world, benefit measured by an improvement in the distance a patient can walk over six minutes.

Sarepta shares more than doubled in value to $8.58 after the new eteplirsen data were released. The stock's rapid rise can be attributed not only to the promising eteplirsen data but also because Sarepta may be able to seek FDA approval without having to conduct another clinical trial under new regulations designed to speed the development and approval of drugs for rare diseases.

Sarepta recently changed its corporate name from AVI Biopharma.

In the study, DMD patients treated weekly with 50 mg of eteplirsen and followed for 36 weeks demonstrated a decline of 8.7 meters in a six-minute walk test compared to baseline. Patients treated with a placebo for 24 weeks followed by eteplirsen for 12 weeks -- the study's control arm -- took the same walking test but showed a decline of 78 meters from baseline.

The treatment benefit favoring eteplirsen as measured by walking distance was 69.4 meters over 36 weeks and was statistically significant, Sarepta said.

"The magnitude of this clinical benefit is an unprecedented treatment effect in DMD. This result represents a major advance in the pursuit of a disease modifying treatment for this severe, progressive and life-threatening disease," said Dr. Jerry Mendell, Director of the Centers for Gene Therapy and Muscular Dystrophy at Nationwide Children's Hospital and principal investigator of the Phase IIb study, in a statement.

DMD is a rare disease and as such, Sarepta enrolled a very small number of patients in this initial study. Just four patients were treated with the 50 mg dose of eteplirsen compared against four patients treated with a placebo and delayed eteplirsen.

The significant, relative improvement in walking ability was sustained when Sarepta analyzed six patients, including two patients treated with a lower, 30 mg dose of eteplirsen. Another two patients treated at the lower dose were excluded because they experienced a sudden and rapid decline in function soon after the study started.

There was no difference in walking ability between patients treated exclusively with the lower eteplirsen dose compared to the control arm, Sarepta said.

Sarepta continues to follow the patients in the study and will have updated results after 48 weeks of treatment ready for presentation at a medical conference in October. On a conference call Tuesday, Sarepta said if the benefit observed in the 36-week data are confirmed at 48 weeks, the company will meet with FDA to discuss regulatory options.

One of those options could be an accelerated approval filing under new FDA regulations designed to speed the development of drugs for rare diseases. Sarepta would still have to conduct a larger clinical trial to confirm eteplirsen's benefit, but the trial could be done post approval.

Last April, Sarepta presented data showing eteplirsen treatment for six months resulted in a statistically significant increase in the production of dystrophin compared to placebo.

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.

In many ways, the science Sarepta is using to find an effective treatment for DMD is similar to the work done successfully by

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What was missing from the April eteplirsen data -- until Tuesday -- was evidence linking increased production of dystrophin to an improved ability to walk. The new data suggests that longer treatment is required before meaningful levels of dystrophin are produced such that it significantly delays progression of DMD and improves walking function, Sarepta said.

--Written by Adam Feuerstein in Boston.

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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;

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