Growth, Body Composition, and Strength of Children With Cystic Fibrosis Treated With Elexacaftor/Tezacaftor/Ivacaftor (ETI)

We prospectively monitored rates of change for growth, body mass and composition, muscle strength, and FEV1 in 6-11-year-olds initiating ETI therapy, comparing them to those of US reference children. We assessed factors potentially contributing to rate of change and report ranges of individual variation. Body composition was assessed using bioelectrical impedance analysis (BIA), and rates of change were analyzed using linear mixed effects regression models. At enrollment, median BMI-Z was 0.6 (IQR: -0.2, 1.1), percent body fat (PBF) was 22.7 (14.0, 31.5), and percent predicted(pp) FEV1 was 100 (90, 106). During ETI treatment, mean Z scores for annualized change rates of BMI (0.02 ± 0.07; p = 0.74), FMI (0.02 ± 0.08; p = 0.76), and FFMI (-0.03 ± 0.07; p = 0.68) were not different from zero. The most rapid weight gain occurred in girls (p = 0.01), 10-11-year-olds (p