ABCB4 and progressive familial intrahepatic cholestasis: In the case of PFIC type 3 (PFIC3, or MDR3 deficiency associated with PFIC), mutations affect the ABCB4 gene, which encodes for multidrug resistance protein 3 (MDR3), a floppase involved in the translocation of phosphatidylcholine (PC) from the hepatocyte membrane to the bile.