Association of pharmacokinetic (CYP2C9) and pharmacodynamic (factors II, VII, IX, and X; proteins S and C; and γ-glutamyl carboxylase) gene variants with warfarin sensitivity

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Abstract
We analyzed mutations of 7 vitamin K—dependent protein and cytochrome P450 2C9 genes in 45 patients and investigated whether any contribute to the large interpatient variability in the warfarin dose-effect relationship. Total clearance and daily dose, INR and INR/Cp, were used as pharmacokinetic and pharmacodynamic indexes, respectively. Patients were grouped by genotype based on a single polymorphism and combinations of polymorphisms. Among the 30 sequence variants identified, CYP2C9*3, 165Thr → Met of the factor II gene, -402G → A, (37-bp repeat)n, and -746T → C of the factor VII gene, and (CAA repeat)n of the γ-glutamyl carboxylase gene were selected as candidate polymorphisms. As the analysis of single polymorphisms implied, the highest INR/Cp mean values and the lowest warfarin maintenance doses were observed in patients homozygous for the 165Met, -402G, (37-bp repeat)6 and -746T alleles. Multiple regression analysis revealed that warfarin sensitivity was independently associated with -402G → A, (CAA repeat)n, CYP2C9*3, and 165Thr → Met, which accounted for 50% of variance. These results suggest that part of the considerable interpatient variation is attributable to genetic variation, and the combined genotyping of CYP2C9 and certain vitamin K—dependent protein genes is useful for predicting anticoagulant responses.