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 (SRPT 4.69%), 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 (GSK -0.20%) 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.