The age-of-onset of chronic P. aeruginosa infection of the lungs in individuals with CF varies widely, and the heritability for age-of-onset of chronic/persistent P. aeruginosa infection of the airway, independent of CFTR genotype, has been estimated to be 0.85 (on a scale of 0 to 1) [12]. This evidence concerns the gene CFTR and cystic fibrosis.