A Phase 3, 2 Part, Randomized, Double-Blind, Placebo Controlled, Parallel Group Study to Evaluate the Pharmacokinetics, Efficacy and Safety of VX 770 in Subjects Aged 6 to 11 Years with Cystic Fibrosis and the G551D Mutation

Part A: To evaluate the pharmacokinetics of a single dose of orally administered VX 770 treatment in subjects 6 to 11 years of age with cystic fibrosis (CF) who have the G551D cystic fibrosis transmembrane conductance regulator (CFTR) mutation on at least 1 allele. Part B: To evaluate the efficacy of VX 770 after 24 weeks of treatment in subjects 6 to 11 years of age with CF who have the G551D CFTR mutation on at least 1 allele.