CD is a genetic cholangiopathy caused by mutations in polycystic kidney and hepatic disease 1 (PKHD1), the gene coding for fibrocystin/polyductin (FPC), a large protein with a single transmembrane domain expressed by cilia and centromers of cholangiocytes and renal epithelial cells [144]. The gene discussed is PKHD1; the disease is Cowden disease.