Long-term effects of birth order and age at diagnosis in cystic fibrosis: A sibling cohort study

Background Siblings with cystic fibrosis (CF) share many genetic and environmental factors but may present different phenotypes. Younger sibs are mostly earlier diagnosed with CF than their older sibs, but might be at risk for an earlier colonization with Pseudomonas aeruginosa (PA) than their older counterparts due to cross‐infection within families. Aims To analyze the effects of birth order and age at diagnosis on lung function, PA colonization, nutritional status, and survival during the first two decades of life in siblings with CF. Methods A retrospective cohort study of 52 sibling pairs was performed in two Dutch CF centers. Data were analyzed both cross‐sectionally and longitudinally using Kaplan–Meier curves and modified log‐rank tests. Results Median age at diagnosis was significantly higher in the older sib compared with the younger sib (3.0 and 0.2 years, respectively, P