CFTR and cystic fibrosis: Cystic fibrosis (MIM 219700) is a systemic autosomal recessive disorder due to LoF variants in the cystic fibrosis transmembrane conductance regulator gene (CFTR; MIM 602421), causing a defective transport of chloride and bicarbonate through the respiratory, biliary, gastrointestinal and reproductive epithelia, resulting in the secretion of thick mucus [8,9].