ATP8B1 and intrahepatic cholestasis: PFIC1 (ATP8B1 disease, OMIM #211600), formerly Byler's disease [41], is the consequence of a severe defect in the gene encoding ATPase, ATP8B1/FIC1 (familial intrahepatic cholestasis 1), localised in the long arm of the 18th chromosome (18q21) [43, 44].