Association of polymorphisms in four bilirubin metabolism genes with serum bilirubin in three Asian populations.

Numerous studies have shown that the (TA)n repeat polymorphism in the uridine diphosphate glycosyltransferase 1 (UGT1A1) gene promoter is associated with hyperbilirubinemia. Several studies also indicated that single nucleotide polymorphism (SNP) rs4148323:G>A at Exon 1 of UGT1A1 is associated with hyperbilirubinemia. However, it remains unclear what role the polymorphisms play in influencing serum total bilirubin (TBIL) levels in general populations, and whether polymorphisms in other genes involved in the bilirubin metabolism pathway are associated with TBIL levels. The present study addressed these questions by investigating the association of four bilirubin metabolism genes with TBIL levels in three Asian populations: 11 genetic polymorphisms in heme oxygenase-1 (HMOX1); biliverdin reductase A (BLVRA); solute carrier organic anion transporter family member 1B1 (SLCO1B1); and UGT1A1. The populations consisted of 502 Kazak herdsmen, 769 Uyghur farmers, and 789 Han farmers, with distinct genetic backgrounds. UGT1A1 was found to be associated with the (TA)(7) allele of the (TA)n repeat polymorphism. We also showed that the A allele of SNP rs4148323:G>A was strongly associated with high TBIL levels in all three populations (each P<0.005). Among polymorphisms in other genes, only the (GT)n repeat polymorphism in the HMOX1 promoter region showed association with TBIL levels in the Uyghur population, but not in the Han and Kazak populations. We also assessed the contributions of (TA)n polymorphism and rs4148323:G>A to phenotypic variations in all three populations. Finally, we observed that significant differences of TBIL levels existed among the three populations; however, this could not be completely explained by the differences at the (TA)n repeat polymorphism and SNP rs4148323:G>A. (c) 2009 Wiley-Liss, Inc.