BACKGROUND: Polymorphisms in the genes encoding the cytochrome P450 2C9 enzyme 
(CYP2C9) and the vitamin K epoxide reductase (VKORC1) are known to contribute to 
variability in sensitivity to coumarins. Patients with certain common genetic 
variants of CYP2C9 (*2 & *3) or a VKORC1 polymorphism (-1639A Allele) require a 
lower dose of coumarin and are also at higher risk for over-anticoagulation and 
serious bleeding. In August 2007, the FDA label for warfarin was updated to 
highlight the benefit of genetic testing to predict warfarin response.
AIM: Since the prevalence of these variants in the Lebanese population has not 
yet been reported, our aim was to determine the genotypes of CYP2C9 and VKORC1 
in our population and to compare allele frequencies with previous findings from 
other ethnic groups.
MATERIALS AND METHODS: CYP2C9 (*1/*2/*3) and VKORC1 (*A/*G) allelic variants 
were assessed by polymerase chain reaction-restriction fragment length 
polymorphism assays in a diversified sample of 161 unrelated healthy Lebanese 
volunteers.
RESULTS: The allele frequencies of CYP2C9 *2 and *3 were 0.112 and 0.096 
respectively, whereas VKORC1-1639A was 0.528. Carriers of the CYP2C9 *2 or *3 
represented 34.2% of the subjects, whereas those of the VKORC1-1639A represented 
73.9%.
CONCLUSION: Our data show no significant difference in the frequency of CYP2C9 
allelic variants when compared to the Caucasian population, whereas the allelic 
frequency of VKORC1-1639A was very high. Over 50% of the Lebanese population 
seem to be carrying more than two independent risk alleles, and is therefore 
potentially at high risk of over-anticoagulation.