A novel functional VKORC1 promoter polymorphism is associated with inter-individual and inter-ethnic differences in warfarin sensitivity

Abstract

Warfarin, a commonly prescribed anticoagulant, exhibited large inter-individual and inter-ethnic differences in the dose required for its anticoagulation effect. Asian populations, including Chinese, require a much lower maintenance dose than Caucasians, for which the mechanisms still remain unknown. We determined DNA sequence variants in CYP2C9 and VKORC1 in 16 Chinese patients having warfarin sensitivity (< or = 1.5 mg/day, n = 11) or resistance (> or = 6.0 mg/day, n = 5), 104 randomly selected Chinese patients receiving warfarin, 95 normal Chinese controls and 92 normal Caucasians. We identified three CYP2C9 variants, CYP2C9*3, T299A and P382L, in four warfarin-sensitive patients. A novel VKORC1 promoter polymorphism (-1639 G > A) presented in the homozygous form (genotype AA) was found in all warfarin-sensitive patients. The resistant patients were either AG or GG. Among the 104 randomly selected Chinese patients receiving warfarin, AA genotype also had lower dose than the AG/GG genotype (P < 0.0001). Frequencies of AA, AG and GG genotypes were comparable in Chinese patients receiving warfarin (79.7, 17.6 and 2.7%) and normal Chinese controls (82, 18 and 0%), but differed significantly from Caucasians (14, 47 and 39%) (P < 0.0001). The promoter polymorphism abolished the E-box consensus sequences and dual luciferase assay revealed that VOKRC1 promoter with the G allele had a 44% increase of activity when compared with the A allele. The differences in allele frequencies of A/G allele and its levels of VKORC1 promoter activity may underscore the inter-individual differences in warfarin dosage as well as inter-ethnic differences between Chinese and Caucasians.

Association of VKORC1 and CYP2C9 polymorphisms with warfarin dose requirements in Japanese patients

“…1). Recently, several groups have demonstrated that polymorphisms in VKORC1 are associated with warfarin sensitivity (D'Andrea et al 2005;Wadelius et al 2005;Yuan et al 2005;Rieder et al 2005;Sconce et al 2005). In a Swedish study, weekly warfarin doses varied significantly, and were associated with four VKORC1 SNPs (5¢ flankingÀ1413A>G, intron 1À136T>C, intron 2+837T>C and exon 3 343G>A), similar to our results (Wadelius et al 2005).…”

“…In a Swedish study, weekly warfarin doses varied significantly, and were associated with four VKORC1 SNPs (5¢ flankingÀ1413A>G, intron 1À136T>C, intron 2+837T>C and exon 3 343G>A), similar to our results (Wadelius et al 2005). Yuan et al (2005) demonstrated that Chinese patients homozygous for the major allele of the À1413A>G polymorphism required a lower warfarin dose than those with other genotypes. The authors also suggested that the promoter polymorphism abolished the E-box consensus sequences, leading to a 44% increase in promoter activity for the minor allele compared to the major allele.…”

“…In the present study, the frequency of allele G in 5¢ flankingÀ1413A>G of VKORC1 in the Japanese population (0.09) was much lower than that in the Swedish population (0.61; Wadelius et al 2005). Thus, the frequency of the AA genotype associated with warfarin sensitivity in Japanese patients (0.83) was much higher than that in Caucasians (0.14) but comparable to Chinese (0.82;Yuan at al. 2005), suggesting that VKORC1 genotype frequencies could account for the interethnic differences in warfarin dose requirements.…”

“…Recently, several groups have demonstrated that noncoding SNPs in VKORC1 influenced warfarin sensitivity (D'Andrea et al 2005;Wadelius et al 2005;Yuan et al 2005;Rieder et al 2005;Sconce et al 2005). These data strongly suggest that differences in genetic variations in both CYP2C9 and VKORC1 could explain the diversity in warfarin sensitivity and dose requirement.…”

The promises of personalized medicine

“…A prospective study addressing the question of whether a priori knowledge of CYP2C9 genotype may improve warfarin therapy demonstrated that patients who were treated applying a CYP2C9 genotype-adjusted algorithm reached a significantly earlier stable anticoagulation state and experienced less minor bleeding [3] than those who were not. Moreover, subjects who are carriers of variants in the vitamin K epoxide reductase complex, subunit 1 (VKORC1) gene require significantly higher warfarin doses than usually recommended [5,30]. In order to estimate appropriate warfarin dosing, algorithms based on both clinical and genetic data obtained from a broad population base have been calculated in a large cohort, thereby achieving a better prediction of subjects requiring lower doses of warfarin for therapeutic anticoagulation [15].…”