In adolescents and adults with CF, lung disease severity is associated with a severe CFTR genotype (the association of two CFTR mutations, including homozygosity for Phe508del, leading to either a complete lack of functioning protein or to a highly unstable protein with minimal activity, is considered as a severe genotype; by contrast, a genotype leading to a residual CFTR function is defined as mild), pancreatic insufficiency, chronic infection with Pseudomonas aeruginosa, presence of CF-related diabetes, lung function impairment and dystrophy [38]. This evidence concerns the gene CFTR and diabetes mellitus.