Although the pancreatic status is closely related to the CFTR genotype [4], there is a wide clinical heterogeneity in CF patients, even between those carrying the same CFTR genotype or between siblings with CF [5], partly explained by environmental factors or by the relevant role of genes other than CFTR, defined as “modifying genes” [6–8]. The gene discussed is CFTR; the disease is cystic fibrosis.