Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Sarepta Therapeutics (NASDAQ:SRPT), a clinical-stage RNA-based therapeutics company focused on treating rare and infectious diseases, roared higher by as much as 36% after presenting at the JPMorgan Healthcare Conference and reporting positive results for lead drug, eteplirsen, in a phase 2b study.

So what: According to Sarepta's press release the company's exon-skipping Duchenne muscular dystrophy drug, eteplirsen, "showed a continued stabilization of walking ability in eteplirsen-treated patients evaluable on the 6-minute walk test" at the 120-week mark. Based on study statistics, patients in both dosing cohorts experienced a decline of 13.9 meters in walking distance, or less than 5%, from baseline. Study 202, as it's known, also demonstrated a statistically significant treatment benefit of 64.9 meters over the placebo. Even the placebo group, which was switched to eteplirsen from week 25 through 120, demonstrated walk-test improvement and have seen only a decline of 9.5 meters in the week 36 through week 120 time frame.

Now what: Yet again we have data that seems to demonstrate that eteplirsen is effective in treating Duchenne muscular dystrophy. The main hang-ups continue to be what the FDA will accept as a primary indicator of success -- because clearly it didn't like the idea that increased dystrophin production equaled success -- and how critical the FDA will be of eteplirsen given the miserable phase 3 results for GlaxoSmithKline (NYSE:GSK) and Prosensa's (NASDAQ:RNA) drisapersen, which delivered no demonstrable clinical benefit in a larger study. The data from its midstage study looks intriguing, for certain, but I'm still sticking to the sidelines until we see how eteplirsen fares in a much larger patient pool.

Sarepta may be skyrocketing higher, but this top stock may leave it in the dust when all is said and done!
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Fool contributor Sean Williams has no material interest in any companies mentioned in this article. You can follow him on CAPS under the screen name TMFUltraLong, track every pick he makes under the screen name TrackUltraLong, and check him out on Twitter, where he goes by the handle @TMFUltraLong.

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