Maintenance warfarin dose varies according to two haplotypes of the vitamin K epoxide reductase gene.

Evaluation of: Effect of VKORC1 haplotypes on transcriptional regulation and warfarin dose. Rieder MJ, Reiner AP, Gage BF et al.: N. Engl. J. Med. 352(22) 2285-2293 (2005). Reider and colleagues examined the association between ten single nucleotide polymorphisms in the vitamin K epoxide reductase complex (VKORC)1 gene and maintenance warfarin dose in patients of European ancestry requiring chronic anticoagulation. Two haplotype groups were associated with warfarin dose after adjusting for covariates using stepwise regression analysis. Together, these two haplotype groups accounted for approximately 25% of the variance in dose. Future research will be required in other populations to evaluate the association of VKORC1 haplotypes and warfarin dose, and to evaluate whether adjusting warfarin dose based on VKORC1 haplotype is superior to standard dosing strategies with respect to the efficacy and safety of warfarin.