What: Shares of clinical-stage Sarepta Therapeutics (NASDAQ:SPRT) dropped more than 11% as of 3:30 p.m. ET after the company received news that its PDUFA decision date has been extended.

So what: The Food and Drug Administration informed Sarepta today that it needed more time to review its New Drug Application for eteplirsen, its potential treatment for Duchenne muscular dystrophy, or DMD. The FDA pushed its decision date back three months and now expects to have an answer by May 26, 2016.

The reason for the delayed decision date can be traced back to additional clinical data that Sarepta handed to the FDA on Jan. 8. That data has been designated by the FDA as a major amendment to the company's NDA submission, and the FDA is demanding an additional three months' time to review the additional data. 

News of having to wait an additional 90 days to hear a decision has put the market in a foul mood, hence why shares are falling. 

Now what: Sarepta Therapeutics' shares have been a basket case for months now as eteplirsen's original PDUFA date has drawn closer. Investors were initially excited about its chances for gaining approval, especially after a competing DMD drug from BioMarin Pharmaceutical (NASDAQ:BMRN) called Kyndrisa received some harsh words at its FDA advisory committee meeting. That seemed to tilt the likelihood of approval in Sarepta's favor, especially since eteplirsen had already been granted priority review and fast-track status. 

However, in January, an FDA advisory committee report raised some serious concerns about Sarepta's eteplirsen, calling into question how efficacious the drug really is and the methodology that the company used to collect data in its clinical trial. Shares of Sarepta tanked after the report was released.

It now looks like we won't have a definitive answer either way until May. There's not much that investors can do between now and then but wait and hope for the best.