After Sarepta Therapeutics (NASDAQ:SRPT) announced that it was going to have a conference call today to update investors about its plans for a marketing application with the Food and Drug Administration, I joked on Twitter that the lede for my article, "I couldn't have predicted this," worked either way.

History said that the FDA wouldn't approve a drug with so little data.

The FDA's recent rhetoric said otherwise.

As it turns out, the news was the most predictable response from the FDA. The agency punted.

When Sarepta last updated us in April, the company said the FDA wanted more information to help the agency decide if Sarepta should file a marketing application for its Duchenne muscular dystrophy drug, eteplirsen, with the limited phase 2 data or wait for a phase 3 trial.

Instead, the FDA told Sarepta that it wouldn't commit to using dystrophin as an acceptable surrogate endpoint for accelerated approval. The agency plans to make that decision based on the data that the company submits with its New Drug Application in the first half of next year. Increased dystrophin protein -- the mutated gene in Duchenne muscular dystrophy -- is the primary endpoint of Sarepta's phase 2 study.

Sarepta also has data that shows eteplirsen helps patients walk farther, which is more convincing since it's a clinical endpoint rather than a surrogate endpoint. There was talk on the conference call today that the six-minute walk data might facilitate a full approval, but that seems like quite a stretch. Sarepta certainly doesn't see that as a high likelihood since it's moving forward with a phase 3 clinical trial that would be required to confirm the phase 2 findings if it gains accelerated approval.

Ironically, phase 3 data from Sarepta's direct competitor -- GlaxoSmithKline (NYSE:GSK) and Prosensa's (NASDAQ:RNA) drisapersen -- that's due in the fourth quarter could help the FDA answer the question about whether dystrophin is an acceptable surrogate endpoint. If increases in dystrophin correlate with clinical outcomes, it would support approving eteplirsen with less data. It's not clear to me whether Glaxo and Prosensa would have to share that correlation with the FDA -- the clinical phase 3 data should be sufficient for approval -- and if it does make those calculations whether the FDA could legally use it to support the approval of another drug since NDA data is proprietary while under patent.

Shares are trading down as I write this, but I think that's likely just a function of traders exiting since the catalyst has been pushed back until next year. For long-term investors, nothing has really changed except they'll have to wait a little longer for a decision on when eteplirsen will be approvedĀ -- possibly with a few more ups and downs before that.

Fool contributor Brian Orelli has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.