There are reports that some variants or a combination of variants is associated with a more severe phenotype but no functional data is available to confirm this.34 Additionally, common variants of the ABCB4 gene have been identified as genetic risk factors for the severe form of ICP in Sweden.22,39 The role of ABCB4 in ICP is further supported by its association with drug-induced cholestasis, where genetic variants of ABCB4 and ABCB11 have been implicated41 including hormonal contraception.42 This evidence concerns the gene ABCB11 and cholestasis.