ABCB4 and bile duct carcinoma: Variants in ABCB4 and ABCB11 are involved in up to 25% of patients with severe ICP.16ABCB4 variants also increase the risk of developing drug-induced intrahepatic cholestasis, gallstone disease, gallbladder and bile duct carcinoma, liver cirrhosis and abnormal liver function tests.17 Variants in several other canalicular transporters or their regulators are implicated in the pathogenesis of ICP, for example, ATP8B1 (ATPase phospholipid transporting 8B1),18NR1H4 (FXR, a principal bile acid sensor) gene19,20 and TJP2 (tight junction protein 2),21 although supporting data are more limited.