Summary
The degree of interpatient variability in the warfarin dose required to achieve the
desired anticoagulant response can only partly be explained by polymorphisms in the
CYP2C9 gene, suggesting that additional genetic factors such as polymorphisms in genes involved
in blood coagulation may influence warfarin dose requirement. In total, 165 Caucasian
outpatients on stable maintenance warfarin treatment previously genotyped for CYP2C9 were analysed for common polymorphisms in FVII, GGCX and VKORC1 genes. The -402G>A polymorphism and a variable number of repeats in intron 7 of FVII gene did not significantly influence warfarin dose.The mean warfarin doses increased
with the number of (CAA) repeats in the GGCX gene, but the differences were significant only in the CYP2C9*1/*1 subgroup of patients (p=0.032). Common polymorphism (6484C>T) in intron 1 of the
VKORC1 gene led to lower warfarin dose requirement; the means were 5.70 (95% C.I. 4.95 -
6.45), 3.49 (3.07 - 3.90) and 2.11 (1.80 - 2.42) mg/day for 6484 CC, CT and TT genotypes,
respectively (p<0.001). In contrast, 9041G>A polymorphism in 3’UTR of theVKORC1 gene led to higher warfarin dose requirement; the means were 3.09 (2.58 - 3.60),
4.26 (3.69 - 4.82) and 5.86 (4.53 - 7.19) mg/day for 9041 GG, GA and AA genotypes,
respectively (p<0.001).With a regression model we explained 60.0% of variability in
warfarin dose, which was due to gene polymorphisms (CYP2C9,VKORC1), age and body-surfacearea. When aiming for individualised warfarin therapy, at least
VKORC1 polymorphisms should be included in predictive genotyping besides CYP2C9.
Keywords
Polymorphism - warfarin - cytochrome P450 2C9 - pharmacodynamic factors - regression
model