Eligibility Criteria:
Inclusion Criteria:
* Diagnosis of DMD or BMD
* Presence of a nonsense mutation in the dystrophin gene
* Unable to ambulate independently for ≥1 year due to DMD/BMD
* Presence of sufficient shoulder and elbow function to perform study-related functional procedures (for example, 9-hole peg test)
* Adequate hepatic, renal, and adrenal function
* Ability to provide evaluable pretreatment echocardiogram and lung function assessments
* Willingness and ability to comply with scheduled visits, drug administration plan, study procedures, laboratory tests, and study restrictions
* Ability to provide written informed consent (parental/guardian consent if applicable)/assent (if \<18 years of age)
Exclusion Criteria:
* Initiation of systemic corticosteroid therapy within 6 months prior to start of study treatment or use of systemic aminoglycoside antibiotic within 3 months prior to start of study treatment
* Use of any intermittent systemic corticosteroid therapy regimen (for example, 10 days on followed by 10 days off, weekend dosing, every-other-day dosing); note that participants must have either been receiving a daily dosing regimen of prednisone, prednisolone, or deflazacort at the time of enrollment into the study or must have not been receiving any systemic corticosteroids
* Any change in treatment for congestive heart failure within 3 months prior to start of study treatment
* Ongoing warfarin or phenytoin therapy
* Prior therapy with ataluren
* Known hypersensitivity to any of the ingredients or excipients of ataluren (Litesse® UltraTM \[refined polydextrose\], polyethylene glycol 3350, Lutrol® micro F127 \[poloxamer 407\], mannitol 25C, crospovidone XL10, hydroxyethyl cellulose, vanilla, Cab O Sil® M5P \[colloidal silica\], magnesium stearate).
* Exposure to another investigational drug within 2 months prior to start of study treatment
* History of major surgical procedure within 1 month prior to start of study treatment or expectation of major surgical procedure (for example, scoliosis surgery) during the 48-week treatment period of the study
* Ongoing immunosuppressive therapy (other than corticosteroids)
* Ongoing participation in any other clinical trial
* Requirement for daytime ventilator assistance
* Uncontrolled clinical symptoms and signs of congestive heart failure
* Prior or ongoing medical condition (for example, concomitant illness, psychiatric condition, behavioral disorder, alcoholism, drug abuse), medical history, physical findings, electrocardiogram (ECG) 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