UDP-glucuronosyltransferase 1A1 (UGT1A1) gene haplotypes and their effect on serum bilirubin concentration in healthy Indian adults.

The aim of the present study was to investigate the allele and genotype frequencies and haplotype structures of the variants in the UGT1A1 gene and their association with serum bilirubin levels in healthy adults. Total serum bilirubin levels were measured in 300 healthy adults (normal hematology and liver function test) and genotyping of seven SNPs was performed by PCR-RFLP, Gene Scan analysis and direct sequencing on the ABI Prism 310 Genetic Analyzer. Of the seven SNPs, four were found to be polymorphic and the frequencies of minor alleles were 0.336, 0.431, 0.353 and 0.066 for -53(TA)7, -3279G, -3156A and 211A respectively. Individuals who carried the -53(TA)7, -3279G and -3156A mutant alleles in homozygous or heterozygous states had significantly higher mean serum bilirubin levels. Five major promoter haplotypes were observed: -53(TA)6/-3279T/-3156G was the most common haplotype, followed by -53(TA)7/-3279G/-3156A, -53(TA)6/-3279G/-3156G, -53(TA)6/-3279G/-3156A and -53(TA)7/-3279T/-3156G with an estimated frequency of 0.445, 0.230, 0.083, 0.065 and 0.050 respectively. Furthermore, the mutant haplotype (-53(TA)7/-3279G/-3156A) was found to have a significant effect on bilirubin concentrations. Promoter polymorphisms and a common haplotype of the UGT1A1 gene are associated with serum bilirubin concentrations and could be a genetic risk factor for hyperbilirubinemia in Indians.