ATP8B1 and progressive familial intrahepatic cholestasis: There are three types of PFIC, classified according to the mutated gene as follows: PFIC type 1 (PFIC1) is due to mutations in the ATP8B1 gene (encoding FIC1); PFIC type 2 (PFIC2), mutations in the ABCB11 gene (encoding bile salt export pump); and PFIC type 3 (PFIC3), mutations in the ABCB4 gene (encoding multidrug-resistant protein 3 [MDR3]).