A Study to Assess Dystrophin Levels in Participants With Nonsense Mutation Duchenne Muscular Dystrophy (nmDMD) Who Have Been Treated With Ataluren

Inclusion Criteria: * Evidence of signed and dated informed consent/assent document(s) indicating that the participant (and/or his parent/legal guardian) has been informed of all pertinent aspects of the trial. * Ambulatory (10 meters walk/run in less than \[\<\] 30 seconds) and functional grade on the Brooke Upper Extremity Scale of a 1 or a 2. * Currently being treated with ataluren 10, 10, 20 mg/kg for \>=9 months, with no gap in treatment of greater than (\>) 1 month, in an ongoing PTC-sponsored nmDMD clinical trial prior to study entry. * Phenotypic evidence of duchenne muscular dystrophy (DMD) based on the onset of characteristic clinical symptoms or signs (for example, proximal muscle weakness, waddling gait, and Gowers' maneuver) by 6 years of age and an elevated serum creatine kinase (CK). Medical documentation of phenotypic evidence of DMD needs to be provided upon request by the medical monitor. * Willing to undergo muscle biopsy. Exclusion Criteria: * Known contra-indication to muscle biopsy (such as bleeding or clotting disorders). * Exposure to another investigational drug within 2 months prior to study enrollment or ongoing participation in any non-ataluren interventional clinical trial. * Requirement for daytime ventilator assistance or any use of invasive mechanical ventilation via tracheostomy. Note: Evening non-invasive mechanical ventilation such as use of bilevel positive airway pressure (Bi-PAP) therapy is allowed. * Prior or ongoing medical condition…