Haplogroup analysis of vitamin-K epoxide reductase (VKORC1) gene: novel element in the optimization of anticoagulant therapy

Warfarin and acenocoumarols are the most commonly prescribed anticoagulants that is difficult to use because of the wide intra- and interpatient variation in the dose requirements, the narrow therapeutic range and the risk of serious bleeding. Vitamin K epoxide reductase (VKORC1) is the site of inhibition by coumarins. Mutations in the VKORC1 gene affect the sensitivity of the epoxy reductase enzyme for warfarin. The three main haplotypes of VKORC1 gene, *2, *3, *4, explain most of the genetic variability in warfarin dose among Caucasians. In the current paper we focus on this subject in view of our experience gained during molecular genetic tests for the main VKORC1 haplotypes in Hungarian patients with anticoagulant therapy and unusual clinical response. A total of 28 selected cases were characterized for VKORC1 G-1639A, G9041A and C6009T alleles. Genotyping has been carried out by molecular biology techniques, including PCR-RFLP assay and direct sequencing. In patients undergoing anticoagulant therapy we could identify VKORC1 *1*2, *2*2, *2*3, *1*4, *2*4 and *3*4 haplotypes. Patients with A haplotype group (14% of the studied patients) require much lower warfarin doses than other patients (2.7+/-0.2 mg/day). In our patients we found some with B haplotype group (25%) who require high warfarin dose (6.2+/-0.3 mg/day). There were also subjects bearing the A/B haplotype group (61%) with intermediate warfarin dose (4.9+/-0.2 mg/day), estimated by the haplotype analyses of the VKORC1 gene. Results presented here underline the need of VKORC1 haplotyping in anticoagulated patients with unusual clinical anticoagulant response, and the examination can have further therapeutic consequences.