PTC Therapeutics has started an international pivotal trial of PTC124 in patients with Duchenne or Becker muscular dystrophy due to a nonsense mutation. The primary objective of this registration-directed Phase IIb trial is to demonstrate the efficacy of PTC124 as measured by improvements in the walking ability of patients with this progressive genetic disease. In this double-blind study, patients will be randomized to receive placebo, or one of two dose levels of PTC124, three times per day. Eligible patients will be boys with nonsense-mutation-mediated Duchenne or Becker muscular dystrophy (DMD/BMD) who are at least five years of age and are able to walk at least 75 meters or approximately 80 yards in six minutes. PTC expects to enroll a total of 165 patients at approximately 35 investigational sites; all study subjects will undergo 48 weeks of blinded treatment. Thereafter, all participants, including those who have been receiving placebo, will be eligible to enroll in an open-label PTC124 extension study. The primary outcome measure is the total distance walked during a 6-minute walk test, a test of ambulation that has now been standardized for boys with DMD/BMD. Other outcome measures in the will evaluate activity at home, muscle and heart function, strength, cognitive ability, muscle integrity, and muscle dystrophin expression. Safety parameters, compliance, and PTC124 blood levels will also be monitored. Future plans for PTC124 include the initiation of longer-term studies in cystic fibrosis, as well as additional proof-of-concept studies in other indications.

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