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 (for example, concomitant illness, psychiatric
condition, behavioral disorder), medical history, physical findings or laboratory
abnormality that, in the investigator's opinion, could adversely affect the safety of
the participant, makes it unlikely that the course of treatment or follow-up would be
completed, or could impair the assessment of study results.