Loss of ATP8B1 function and downregulation of cystic fibrosis transmembrane conductance regulator (CFTR) in biliary cells can lead to impaired bile acid excretion and may contribute to the development of extrahepatic cystic fibrosis in PFIC1 patients (Demeilliers et al., 2006). This evidence concerns the gene ATP8B1 and cystic fibrosis.