Association of warfarin dose with genes involved in its action and metabolism

Abstract

We report an extensive study of variability in genes encoding proteins that are believed to be involved in the action and biotransformation of warfarin. Warfarin is a commonly prescribed anticoagulant that is difficult to use because of the wide interindividual variation in dose requirements, the narrow therapeutic range and the risk of serious bleeding. We genotyped 201 patients for polymorphisms in 29 genes in the warfarin interactive pathways and tested them for association with dose requirement. In our study, polymorphisms in or flanking the genes VKORC1, CYP2C9, CYP2C18, CYP2C19, PROC, APOE, EPHX1, CALU, GGCX and ORM1-ORM2 and haplotypes of VKORC1, CYP2C9, CYP2C8, CYP2C19, PROC, F7, GGCX, PROZ, F9, NR1I2 and ORM1-ORM2 were associated with dose (P < 0.05). VKORC1, CYP2C9, CYP2C18 and CYP2C19 were significant after experiment-wise correction for multiple testing (P < 0.000175), however, the association of CYP2C18 and CYP2C19 was fully explained by linkage disequilibrium with CYP2C9*2 and/or *3. PROC and APOE were both significantly associated with dose after correction within each gene. A multiple regression model with VKORC1, CYP2C9, PROC and the non-genetic predictors age, bodyweight, drug interactions and indication for treatment jointly accounted for 62% of variance in warfarin dose. Weaker associations observed for other genes could explain up to approximately 10% additional dose variance, but require testing and validation in an independent and larger data set. Translation of this knowledge into clinical guidelines for warfarin prescription will be likely to have a major impact on the safety and efficacy of warfarin.

Fig. 1

An overview of the interaction between warfarin and the 29 genes. This pathway illustrates genes thought to mediate the effects of warfarin. It also depicts a simplified representation of the biotransformation of warfarin and vitamin K

Fig. 2

Fine mapping of the VKORC1 locus. a Location of SNP markers (MAF ≥ 5%) in a ∼550 kb region surrounding VKORC1 which is coded on the reverse strand and is located at the right end of the LD block. Previously reported SNPs are shown in red (11). b The univariate r² (pink, left axis) and P-value (blue, right axis) are shown for each SNP. The black line near 10⁻³ on the right axis indicates the P-value that is necessary to achieve significance after within-gene Bonferroni correction. c HaploView analysis with pair-wise r² illustrating the extent of LD in the region. The red dotted triangle indicates the LD block defined with data of the HapMap project (CEU panel)