CFTR and cystic fibrosis: Cystic Fibrosis (CF; MIM: 219700) is a multi-system autosomal recessive rare disease caused by pathogenic, ‘CF-causing’, variants (henceforward mutations) in the Cystic Fibrosis Transmembrane Conductance Regulator (CFTR; MIM: 602421) gene (Riordan et al. 1998).