Prosensa (UNKNOWN:RNA.DL) and partner GlaxoSmithKline (NYSE:GSK) announced stunning news today. The two partners' experimental drug drisapersen failed to meet the primary endpoint in a late-stage study for treatment of Duchenne muscular dystrophy, or DMD. Prosensa's shares collapsed more than 70% in early trading. Is this biotech now doomed to oblivion?

Assessing the failure
The goal was for drisapersen to significantly improve results in the standard six-minute walking distance test used to assess DMD patients. That didn't happen. 

125 boys were given a 6 mg/kg/week dose of drisapersen, and an additional 61 boys took placebo in a double-blind phase 3 study conducted over a 48-week period. Unfortunately, there were no statistically significant differences in walking ability between the two groups. Furthermore, there weren't significant differences in any of the secondary assessments of motor ability between the groups.

Prosensa CEO Hans Schikan said that, despite the disappointment, his company remains "committed to the overall program" and will continue working with Glaxo. The two companies will now examine the results in more detail. Carlo Russo, head of GlaxoSmithKline's rare diseases research and development, said that this further analysis will help determine what the next steps might be for drisapersen.

The limited information released from the phase 3 study didn't provide even an inkling of good news. Reaction from the market appears to have written off drisapersen's chances. However, we really do have to wait and see what the full analysis reveals. There could still be hope that the drug can help DMD patients, although that hope appears dim right now.

Collateral damage?
Prosensa does have a couple of other drugs in clinical studies. However, both of these drugs rely on exon-skipping just as drisapersen does. The absolute worst-case scenario would be that exon-skipping is found to just not work for DMD. If that's the case, Prosensa can throw in the towel. It's over.

For that matter, Sarepta Therapeutics (NASDAQ:SRPT) would be in the same dire predicament in that scenario. Eteplirsen also uses the exon-skipping approach. It's way too early to assume anything along those lines, though.

The market seemed to be desperately trying to process what the drisapersen news could mean for Sarepta. Shares were up then down in both pre-market trading and after the markets opened. 

One one hand, the failure of its chief rival in developing a treatment for DMD could mean good news for Sarepta. It clears the path for the biotech to basically have the worldwide DMD market to itself if eteplirsen gains approval -- at least for a while.

On the other hand, Prosensa's study including 186 patients highlights just how small Sarepta's mid-stage eteplirsen study with only 12 patients was. The odds that the U.S. Food and Drug Administration demands a larger study from Sarepta seem to have increased after today's news. That would push possible approval for eteplirsen back considerably.

Those of us involved in the world of health care investing often focus more on the companies and investors affected by bad news like this. The sad reality, though, is that the biggest collateral damage of all could be for the young boys suffering from DMD and their families. For their sake, let's all hope that good news somehow comes out of this latest setback.

Fool contributor Keith Speights 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.