ABCB4 and progressive familial intrahepatic cholestasis: There are three major proteins affected in PFIC, including the bile salt export pump (BSEP) encoded by ABCB11, multidrug resistance protein 3 (MDR3) encoded by ABCB4, and a membrane lipid composition protein (FIC1) encoded by ATP8B1, while three other reported proteins may be affected in PFIC patients, including tight junction protein 2 encoded by TJP2, the farnesoid X receptor (FXR) encoded by NR1H4, and myosin 5B encoded by MYO5B (Sambrotta et al., 2014; Qiu et al., 2017; Keitel et al., 2019).