Chicago, IL, March 17, 2014 (GLOBE NEWSWIRE) -- Prosensa Holding N.V. (NASDAQ: RNA), the Dutch biopharmaceutical company focusing on RNA-modulating therapeutics for rare diseases with high unmet need, today reported encouraging 48-week data from its U.S.-based, Phase II placebo-controlled study (DMD114876 or DEMAND V) of its lead compound, drisapersen, for the treatment of Duchenne Muscular Dystrophy (DMD). The results of this study indicate that, compared to placebo, boys in the higher-dose drisapersen group (6 mg/kg once weekly) experienced stabilization and even improvements in their muscle function and physical activity as measured by the six-minute walk test (6MWT) for the 24-week treatment phase and maintained this improvement during the 24-week follow-up period. Additionally, when evaluating the percent-predicted six-minute walk distance (6MWD), a clinically meaningful treatment difference of 5.2% was observed at week 24 and 4.8% at week 48. Principal investigator, Craig M. McDonald, M.D., Professor and Chair of Physical Medicine & Rehabilitation and Professor of Pediatrics at the University of California, Davis School of Medicine, will report the 48 week results in a poster session (Abstract #50) today at the Muscular Dystrophy Association 2014 Clinical Conference in Chicago, Illinois (March 16-19). "Given the severity of the disease and the lack of disease modifying treatment options available, the results of this important study support the use of drisapersen at a dose of 6 mg/kg once weekly in the treatment of boys with DMD eligible for exon 51 skipping" Dr. McDonald said. "The maintenance of the clinically meaningful treatment benefit in the 24-week follow-up phase is very encouraging evidence for the drug's ability to produce prolonged stabilization of disease and may indicate that, at the 6 mg/kg once weekly dose, the drug has a long term treatment effect that helps delay disease progression in younger, less severe boys." The study included 51 boys with DMD who were at least five years old, still able to walk and stand up from the floor without help in less than 15 seconds. As previously reported, boys in the group who received a 6mg/kg dose of drisapersen each week for the 24-week treatment period show a 27.1 meter improvement in the 6MWT (including a 16.1 m increase from baseline) over the boys in the placebo group at the end of the treatment period (p=0.069), indicating a clinically meaningful outcome for the primary endpoint. This study compared 6mg/kg/week with 3mg/kg/week and placebo and was not statistically powered to show a significant difference between the arms. A clinically meaningful treatment difference of 27.9 m over placebo (p=0.177) was maintained for 24 weeks after drisapersen administration ceased. This includes an overall mean increase from baseline of 14.7 m. In the drisapersen 6 mg/kg/week group, an improvement was seen in the percent-predicted 6MWD of 5.2% (p=0.051) and 4.8% (p=0.154) when compared to placebo at weeks 24 and 48, respectively.