UDP-glucuronosyltransferases (UGTs) play a major role in the conjugation and therefore elimination of potentially toxic xenobiotics and endogenous compounds. The 1-4 isoform UGT1A4 is able to act upon lipophilic bilirubin, the end product of heme breakdown. Defects in UGT1A4 can cause hyperbilirubinemia syndromes ranging from mild forms such as Gilbert syndrome (GILBS; MIM:143500) to the more severe Crigler-Najjar syndromes 1 and 2 (CN1, CN2; MIM:218800 and MIM:606785) (Sticova & Jirsa 2013, Strassburg 2010, Udomuksorn et al. 2007, Costa 2006, Maruo et al. 2000).