Uridine diphosphate (UDP)-glucuronosyl transferase 1A1 (UGT1A1) is responsible for bilirubin conjugation with glucuronic acid.Genetic mutations in the UGT1A1 gene may cause reduced or absent UGT1A1 enzymatic activity resulting in hyperbilirubinemia (eg, Gilbert syndrome, Crigler-Najjar syndrome).
There are case reprots suggesting that patients on irinotecan can have severe toxicity if they have a mutaiton of this gene. There are no guidelines that recomemdn routine testing of all patients prior to inrinotecan chemotherapy.
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Oncology: an evidence-based approach By Alfred E. Chang, p.37, 2005