In the US disease-progression cohort, which was used in this model-validation exercise, Volkova et al. analyzed 805 people with CF aged ≥6 years who initiated ivacaftor treatment in 2012 as well as 3815 people with CF not eligible for ivacaftor (the only CFTRm available in 2012); the populations were matched on age, sex, and disease severity (by CFTR genotype) [18]. This evidence concerns the gene CFTR and cystic fibrosis.