[The c.-1639g > A polymorphism of the VKORC1 gene and his influence on the therapeutic response during oral anticoagulants use].

Background/aim: A single nucleotide polymorphism c.-1639G > A in the promoter region of vitamin K-epoxide reductase (VKORC1) gene has been found to account for most of the variability in response to oral anticoagulants (OA). The aim of the study was to determine the incidence and the effect of c.-1639G > A polymorphism on the acenocoumarol dosage requirements in the group of patients under stable anticoagulation, and to estimate the variability in response to OA.

Methods: Our study included 200 consecutive patients requiring low (n = 43), medium (n = 127) and high (n = 30) acenocoumarol dose.

Results: Out of 43 low dose patients, 40 (93%) carried the A allele. The A allele was less frequent in the group of 30 patients requiring high dose: among these patients 13 (43.3%) carried the A allele in the heterozygous form and none of them carried AA genotype. The patients with GG genotype required 2.6 times higher dose than the patients carriers of AA genotype (p < 0.0001). In 33 patients (16.5%) the overdose occurred during the initiation of anticoagulant therapy and in 11 patients (5.5%) it was associated with bleeding. Out of the group of 33 overdosed patients, 27 and 6 patients carried AA and GA genotype, respectively (p < 0.000001).

Conclusion: VKORC1 significantly influenced OA dose and predicted individuals predisposed to unstable anticoagulation. The carriers of AA genotype required 2.6 time lower doses of OA than the carriares of GG genotype. Pharmacogenetic testing could predict a high risk of overdose among 28.5% of our patients--carriers of AA genotype, before anticoagulation therapy initiation.