Schlüter DK, Ostrenga JS, Carr SB, et al. - In the present study, the researchers sought to compare longitudinal trajectories of lung function in children with cystic fibrosis (CF) between the USA and UK, as well as to investigate the reasons for any differences. Mixed-effects regression analysis was used to model lung function trajectories in the study populations. The sample consisted of 9,463 children from the USA and 3,055 children from the UK with homozygous F508del genotype. Findings revealed that children with CF and homozygous F508del genotype in the USA had better lung function compared with UK children. Early growth or nutrition may not seem to explain these variations, but differences in the use of early treatments should be investigated further.