Copy-number variations (CNVs) of the human sex steroid metabolizing genes UGT2B17 and UGT2B28 and their associations with a UGT2B15 functional polymorphism

Abstract

UGT2B17 and UGT2B28 are among the most commonly deleted genes in humans and encode members of the uridine diphosphate (UDP)-glucuronosyltransferase 2B (UGT2B) subfamily. They are involved, along with UGT2B15, in the catabolism of sex-steroid hormones. Despite the recent biomedical interest in UGT2B17 and UGT2B28 copy-number variations (CNVs) within human populations, the impact of their gene dosage has been hampered by the lack of precise molecular identification of the common deletion breakpoints within high homology sequence regions on chromosome 4. We have characterized these common deletions and report their coexistence in Caucasians, along with the p.D85Y (rs1902023:G>T) functional polymorphism of UGT2B15. Segmental duplications of 4.9 kb for UGT2B17 and 6.8 kb for UGT2B28 comprise purine-rich recombination sites located 117 kb and 108 kb apart on both ends of the deletions. CNVs of UGT2B17 and UGT2B28 occur in Caucasians at 27% and 13.5%, respectively. While only 43% have two copies of both genes, 57% harbor at least one deletion. Their co-occurrence on 5% of chromosomes creates a 225-kb genomic gap. CNVs of both UGT2B17 and UGT2B28, with the co-occurrence of UGT2B15:p.D85Y, generate seven distinct haplotypes. Restricting the analyses to CNV of the UGT2B17 gene without evaluating UGT2B28 CNV, along with the genotype of UGT2B15, may over- or underestimate the impact of each gene under physiological conditions or disease states.