ATP8B1 and progressive familial intrahepatic cholestasis: Manifestations and severity of PFIC are determined by the loss of function of liver transport proteins caused by mutations such as of ATP8B, ABCB11 and ABCB4 in PFIC1 to 3, resulting in reduced function of PFIC-associated protein 1 (FIC1), bile salt export pump (BSEP) and multidrug resistance protein 3 (MDR3) (1, 4).