UGT1A1 (Uridine Diphosphate Glucuronosyltransferase 1A1) belongs to the UGT family, responsible for conjugating glucuronic acid with small molecule substrates, enhancing their solubility and promoting excretion. UGT1A1 is primarily expressed in the liver, and also found in the intestine, kidneys, and other tissues. It plays a key role in drug metabolism and bilirubin clearance. Its specific expression pattern plays a significant role in individual differences in drug responses. Mutations in the UGT1A1 gene, such as polymorphisms seen in Gilbert's syndrome, can lead to bilirubin metabolism disorders and jaundice.