GlaxoSmithKline and Prosensa have suffered a major disappointment after drisapersen, their investigational drug for Duchenne muscular dystrophy failed a late-stage trial.

GSK’s Phase III study of drisapersen did not meet the primary endpoint of a statistically significant improvement of distance walked in six minutes compared to placebo. There was no treatment difference in key secondary assessments of motor function, notably a ten-metre walk/run test and a four-stair climb.

The trial involved 186 boys suffering from DMD, a severely debilitating childhood neuromuscular disease that affects one in 3,500 live male births and is caused by mutations in the dystrophin gene. The failure comes just three months after the US Food and Drug Administration granted breakthrough therapy designation to drisapersen.

Carlo Russo, head of GSK rare diseases R&D, said "we are committed to evaluating the outcome of this study in the context of the overall development programme with experts in the field, and we expect such evaluation to help inform our next steps for drisapersen". Prosensa chief executive Hans Schikan added that “while we are disappointed that this study did not meet its primary endpoint, we remain committed to the overall programme and will continue to work closely with GSK".

The news saw Prosensa shares collapse 70.3% to 7.14 euros, while those of Sarepta Therapeutics, which is developing a rival treatment for DMD called eteplirsen (which is also an exon-skipping drug) leapt 18.2% to $43.30.

Commenting on the news, Debra Miller, chief executive of CureDuchenne, a US nonprofit organisation, said that while the results were disappointing, "we hold out hope that they will provide critical information to the research community that can be applied in future studies". She went on to say that "we are fully confident in the exon-skipping technology as a viable platform to develop a treatment for Duchenne and Duchenne families should not give up hope".