MDR3 (multidrug resistance3) deficiency in humans (MDR2 in mice)causes progressive familial intrahepatic cholestasis type 3 (PFIC3).PFIC3 is a lethal disease characterized by an early onset of intrahepaticcholestasis progressing to liver cirrhosis, a preneoplastic condition,putting individuals at risk of hepatocellular carcinoma (HCC). The gene discussed is ABCB4; the disease is progressive familial intrahepatic cholestasis type 3.