Pharmacogenetics research on chemotherapy resistance in colorectal cancer over the last 20 years

Figure 6 Graphic representation of the human UGT1A gene locus encoding the UGT1A enzymes and the major UGT1A1, 1A7 and 1A9 polymorphisms that are responsible for glucuronidation of SN-38. Individual first exons are positioned at the 5’ end of the chromosome and common exons 2-5 at the 3’ end. Individual exon 1 sequences are combined with exons 2-5 sequence, which is present in every UDP-glycosyltransferase 1A1 (UGT1A1) transcript, the intervening sequence of the primary transcript is eliminated by splicing[404]. The promoter variant, UGT1A1*28, *36 and *37 results from a TA insertion/deletion in the (TA)₆TAA element of the UGT1A1 promoter region. This alteration leads to decreased/increased gene expression[184].