Pfizer (NYSE:PFE) released fairly promising data from its trial for the gene therapy PF-06939926 in boys with Duchenne muscular dystrophy. As the long code name implies, the drug is still in an early stage of development, but the data was fairly impressive nonetheless.

In a phase 1b clinical trial, treatment with PF-06939926 resulted in expression of dystrophin, the protein that's missing in patients with Duchenne muscular dystrophy. The three patients given the lower dose had an average of 24% of normal expression of dystrophin in muscle biopsies taken 12 months after treatment with PF-06939926. The three patients treated at the higher dose averaged an even more impressive 51.6% of normal expression of dystrophin.

More importantly, the dystrophin expression appears to be helping the muscles function better. Using the 

The six patients improved their scores on the North Star Ambulatory Assessment (NSAA) -- a measure of muscle function with a top score of 34 -- by an average of 3.5 points. The study didn't have a control group, but based on historical data for untreated Duchenne patients, those patients would have been expected to lose an average of 4 points on the NSAA scale in one year.

Doctor examining a baby's foot

Image source: Getty Images.

Based on the promising data, Pfizer plans to go straight into a phase 3 clinical trial starting in the second half of this year. Beyond the obvious fact that it is aiming to fill an as-yet unmet need for Duchenne patients, Pfizer's decision to skip the phase 2 step may also be due to the competition with Sarepta Therapeutics (NASDAQ:SRPT).

It's hard to compare results from different clinical trials since they may have enrolled patients at different stages of disease progression, but in its clinical trial, Sarepta Therapeutics' gene therapy SRP-9001 produced a 6-point improvement on the NSAA. The biotech expects data from a placebo-controlled clinical trial of SRP-9001 in the first quarter of next year.

Investors seemed to be willing to look past the issues with cross-clinical-trial comparisons and sent shares of Sarepta Therapeutics up by 11.5% as of 3:30 p.m. EDT on Friday, while shares of much-larger Pfizer were trading down a fraction of a percent.