CFTR and exocrine pancreatic insufficiency: Cystic fibrosis is caused by mutations in the CFTR gene with manifestations of pancreatic insufficiency, pulmonary abnormalities such as recurrent and chronic bronchopulmonary infections, bronchiectasis, and chronic obstructive pulmonary disease, and congenital bilateral absence of the vas deferens (CBAVD), which causes male infertility [20, 21].