In nonsense mutation DMD (nmDMD), early start of treatment is important and necessary and, therefore, it is relevant to understand the correct and tolerable dose in this age group, particularly since ataluren is dosed by weight. This study included a 4-week screening period, a 52-week treatment period (the first 4 weeks of which included PK parameters), and a 4-week follow-up period for participants who completed the treatment period (60 weeks total duration). The objective of the extension period (treatment period after PK parameters have been completed) was to assess the long-term safety of chronic administration of ataluren in this participant population.