LAUSR

Abstract The role that the phase-II reaction, glucuronidation, plays in the biotransformation of endo and xenobiotics is discussed with particular emphasis given to the UGT1A1 isoenzyme. This individual isoenzyme is responsible for both the mono and di-glucuronidation of bilirubin together with the glucuronidation of a number of xenobiotics of clinical interest (irinotecan, belinostat, atazanavir, pegvisomant). The review then discusses the roles that the various allelic variants of the UGT1A1 gene play in bilirubin metabolism and in particular how these allelic variants are involved in the clinical manifestation of the diseases of GS, CN1 and CN2. The review concludes with the roles that the UGT1A1*28 and UGT1A1*6 alleles play in adverse drug reactions (decreased glucuronidation of irinotecan, belinostat, atazanavir, pegvisomant) leading to increased exposure, reduced clearance and neutropenia (irinotecan, belinostat), increased risk for jaundice and hyperbilirubinaemia (atazanavir) and liver toxicity (pegvisomant) before discussing the future role of UGT1A1 in personalised medicine.