However, accumulation of BAs in the liver can be very toxic, something that happens in diseases resulting from impaired BSEP function or expression, like progressive familial intrahepatic cholestasis type 2 (PFIC2), intrahepatic cholestasis of pregnancy, drug-induced cholestasis, and liver cancer [3]. This evidence concerns the gene ABCB11 and progressive familial intrahepatic cholestasis type 2.