APOE genotype makes a small contribution to warfarin dose requirements.

Alterations in vitamin K availability can significantly influence anticoagulation response to warfarin. Apolipoprotein E (APOE) plays a part in the hepatic uptake of lipid-soluble vitamin K. This study aimed to determine the influence of common polymorphisms in the APOE gene on warfarin dose requirements. patients with stable anticoagulation control and with a target International Normalized Ratio (INR) 2.0-3.0 were genotyped for the APOE epsilon2, epsilon3 and epsilon4 variants. Mean +/- SD daily warfarin doses were significantly lower in patients carrying at least one epsilon4 allele compared to the epsilon3epsilon3 reference genotype (3.3 +/- 1.9 versus 4.0 +/- 1.8; P = 0.03; 95% CI: 0.1-1.2). Multivariate regression analysis showed that patient age, height and CYP2C9, VKORC1 and APOE genotypes significantly contributed to warfarin dose requirement (R = 57%). only the epsilon4 allele of APOE was found to make a significant (P = 0.002) but small contribution to warfarin dose requirement. There was no significant difference in fasted plasma vitamin K concentration between patients with the different APOE genotypes. This study suggests that APOE genotype is unlikely to have a clinically significant effect on warfarin dose requirements.

The impact of CYP2C9 and VKORC1 genetic polymorphism and patient characteristics upon warfarin dose requirements: proposal for a new dosing regimen.

Current dosing algorithms do not account for genetic and environmental factors for warfarin dose determinations. This study investigated the contribution of age, CYP2C9 and VKORC1 genotype, and body size to warfarin-dose requirements. Studied were 297 patients with stable anticoagulation with a target international normalized ratio (INR) of 2.0 to 3.0. Genetic analyses for CYP2C9 (*2 and *3 alleles) and VKORC1 (-1639 polymorphism) were performed and venous INR and plasma R- and S-warfarin concentrations determined. The mean warfarin daily dose requirement was highest in CYP2C9 homozygous wild-type patients, compared with those with the variant *2 and *3 alleles (P < .001) and highest in patients with the VKORC1 (position -1639) GG genotype compared with those with the GA genotype and the AA genotype (P < .001). Mean warfarin daily dose requirements fell by 0.5 to 0.7 mg per decade between the ages of 20 to 90 years. Age, height, and CYP2C9 genotype significantly contributed to S-warfarin and total warfarin clearance, whereas only age and body size significantly contributed to R-warfarin clearance. The multivariate regression model including the variables of age, CYP2C9 and VKORC1 genotype, and height produced the best model for estimating warfarin dose (R2 = 55%). Based upon the data, a new warfarin dosing regimen has been developed. The validity of the dosing regimen was confirmed in a second cohort of patients on warfarin therapy.

Upstream and coding region CYP2C9 polymorphisms: correlation with warfarin dose and metabolism.

OBJECTIVES: To assess whether CYP2C9 alleles other than CYP2C9*2 and *3 are associated with a low-warfarin dose requirement and the relevance of upstream CYP2C9 polymorphisms to dose requirement and metabolism. METHODS: CYP2C9 exons, intron-exon boundaries and 3 kb of upstream sequence in 20 patients requiring or= 0.01, was obtained. In individuals negative for coding region polymorphisms, neither individual genotypes for T-1188C or DeltaG-2664DeltaT-2665 or particular combinations of haplotype pairs were predictive of dose requirement or S-warfarin total clearance, suggesting neither upstream polymorphism was functionally significant. Dose requirements in CYP2C9*11 heterozygotes were not statistically significantly different from homozygous wild-type individuals. CONCLUSIONS: The coding region non-synonymous polymorphisms associated with the CYP2C9*2 and CYP2C9*3 alleles are the major CYP2C9-related factor affecting warfarin dose in UK Caucasians. Upstream CYP2C9 polymorphisms do not appear to be important independent determinants of dose requirement.