CAMBRIDGE, Mass. (TheStreet) -- Sarepta Therapeutics (SRPT) - Get Report is revealing for the first time Thursday new data on its Duchenne muscular dystrophy drug eteplirsen which the company believes make a strong case supporting U.S. approval early next year.

The new findings include an analysis showing all of the Duchenne patients treated with eteplirsen in Sarepta's phase II study had a significantly slower rate of disease progression over three years compared to a matched set of untreated Duchenne patients culled from external studies.

Independent analysis of muscle tissue samples also showed increased production of dystrophin, a key protein necessary for proper muscle function, in Duchenne patients treated with eteplirsen compared to untreated patients. Duchenne patients have a genetic mutation which renders them unable to make functional dystrophin. Eteplirsen is designed to correct this defect.

Sarepta interim CEO Ed Kaye says the new eteplirsen data were compiled in response to questions raised by the U.S. Food and Drug Administration about the small size of Sarepta's phase II study, which enrolled just 12 boys with Duchenne.

"We know there were concerns about the limited number of patients, so we listened to the FDA and came up with ways to supplement the database," said Kaye, speaking to me from near London late Wednesday night (very early Thursday morning for him), where the new eteplirsen data are being presented at a meeting of the World Muscle Society.

Sarepta is asking FDA to approve eteplirsen on an accelerated, or conditional, basis. This would make eteplirsen available to Duchenne patients now (and allow Sarepta to generate revenue) while the company completes an ongoing, larger study to confirm the drug's efficacy and safety.

There are no drugs approved currently to treat Duchenne, which causes kids to become wheelchair-bound in their teens and die as young adults.

"There are [Duchenne] kids who have been waiting since 2007 to get a drug. With this supplemented eteplirsen dataset, I think we make a very good case that the time is now for accelerated approval," said Kaye.

In the past, Sarepta has presented efficacy data from its phase II study by comparing the walking ability of six patients treated with eteplirsen continuously against four patients treated initially with a placebo but who then transitioned to eteplirsen. Another two patients enrolled in the study were treated with eteplirsen but dropped out because they lost the ability to walk.

At the FDA's request, Sarepta is now comparing all 12 Duchenne patients enrolled in its phase II study against 13 Duchenne patients culled from two different natural history studies. Sarepta chose these 13 patients for the comparator arm because they all had baseline characteristics which matched up well against the eteplirsen-treated patients.

Measured at three years, the 12 eteplirsen-treated patients were able to walk 151 meters more in six minutes compared to the 13 patients in the matched external control arm. The difference in walking ability benefiting eteplirsen was statistically significant, Sarepta said.

At three years, only two eteplirsen-treated patients out of 12 enrolled became wheelchair-bound compared to six of the 13 untreated patients in the matched control arm.

Ten of the 12 eteplirsen-treated patients maintain the ability to walk four years after enrolling in the phase II study.

Sarepta has previously presented findings from biopsies of muscle tissue taken from the 12 patients in its phase II study showing that eteplirsen could produce functional dystrophin. These data were controversial and deemed somewhat unreliable, however, because the methods used to measure dystrophin are imprecise.

Again at FDA's request, Sarepta used a new method, the western blot, to measure dystrophin production in new muscle tissue samples taken from 11 of the 12 patients treated with eteplirsen in the phase II study. The result: nine of the 11 eteplirsen-treated patients has measurable dystrophin production, assessed by independent monitors.

Sarepta also conducted the same western blot analysis on muscle tissue from nine untreated Duchenne patients, but only one of these samples showed measureable dystrophin.

All the eteplirsen data presented Thursday has been submitted to the FDA as part of the company's approval package. The FDA is expected to make an approval decision by Feb. 26, 2016.

Before that happens, FDA is expected to convene a panel of outside experts to review the eteplirsen data. Sarepta CEO Kaye says FDA has still not informed the company about a final date for the advisory panel, but Nov. 23 to 24 remains listed on the FDA Web site as tentative dates.

The same FDA advisory panel, whenever it is scheduled, will also review Biomarin Pharmaceuticals' (BMRN) - Get Reportcompeting Duchenne drug drisapersen. Biomarin submitted drisapersen to FDA two months ahead of Sarepta, so its approval decision date is Dec. 27.

During our phone call Wednesday night, I asked Kaye if providing FDA with the new eteplirsen data in response to its questions about the phase II study improved the odds for approval.

"I can tell you that the FDA tone is completely different today from what it was six months ago. We've had about 70 correspondences since the new drug application was filed. We've had several meetings with them to make sure they understood the data and that it was presented in a format that they wanted," Kaye said.

He continued, "Ultimately, the decision will come down to the [advisory] panel and the FDA. They have the responsibility to approve the drug and we have the responsibility to make sure we present the data as best we can. Let me put it this way, I'm not embarrassed to stand up in front of the FDA and present these data because I believe it's a reasonable data set for accelerated approval."

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.