Polymorphisms of the human UDP-glucuronosyltransferase (UGT) 1A7 gene in colorectal cancer

Background: Genetic polymorphisms in the human UDP-glucuronosyltransferase-1A7 (UGT1A7) gene are detected and significantly correlated with sporadic colorectal carcinoma. UGT1A7, which has recently been demonstrated to glucuronidate environmental carcinogens, is now implicated as a Cancer risk gene. A silent mutation at codon 11 and missense mutations at codons 129, 131, and 208 lead to the description of three polymorphic alleles designated UGT1A7*2, UGT1A7*3, and UGT1A7*4.

Methods: UGT1A7 polymorphisms were analysed by polymerase chain reaction amplification and Sequencing, as well as temperature gradient gel electrophoresis in 210 healthy blood donors and 78 subjects with colorectal Cancer.

Results: Homozygous wild-type UGT1A7 alleles were present in 20% of normal controls but were only detected in 9% of patients with colorectal carcinoma (odds ratio (OR) 0.39 (95% confidence interval (CI) 0.17-0.92); p=0.03). Analysis of individual polymorphic alleles identified a highly significant association between the presence of UGT1A7*3 alleles and colorectal Cancer (OR 2.75 (95% CI 1.6 - 4.71); p<0.001). Recombinant expression of UGT1A7 polymorphic cDNA in eukaryotic Cell Culture showed reduced carcinogen glucuronidation activity in comparison with wild-type UGT1A7. UGT1A7 may therefore represent a modifier gene in colorectal carcinogenesis.

Conclusion: We have identified a potential novel risk factor in sporadic colorectal Cancer which may contribute to the identification of risk groups and to the elucidation of factors involved in colon carcinogenesis.