The CYP2C9 gene is localized on chromosome 10 (locus 10q24); its length is 55,000 base pairs (bp). To date, more than 20 allelic variants have been identified for this gene. The most common allelic variant is CYP2C9 *! (wild-type allele). In individuals in whose genotype only wild-type alleles are present, the biotransformation of coumarins proceeds with a normal intensity, and average therapeutic doses and levels of MHO are most acceptable for such people. The study of allelic variants CYP2C9 * 2 and CYP2C9 * 3, as the most common after the "wild type" allele, showed that they are associated with higher concentrations of S-warfarin in blood plasma, as well as with lower values ​​of its clearance, due to for slowing down biotransformation. Moreover, it has been shown that the risk of bleeding in patients whose genotype contains allelic variants CYP2C9 * 2 and CYP2C9 * 3 increases 2-3 times.

Despite the large number of allelic variants of the CYP2C9 gene discovered to date (which indicates a high research interest in this issue), most of them have not been sufficiently studied. The CYP2C9 * 4 allele is found only in Mongoloids, and its frequency is low. Variants CYP2C9 * 5 and CYP2C9 * 6 occur with a frequency of no more than 1% in Negroids and are practically absent in Mongoloids and Caucasians. The most common and well-studied variations in influencing drug response with warfarin are the CYP2C9 * !, CYP2C9 * 2 and CYP2C9 * 3 alleles [Herman et al., 2005].

Allelic variants CYP2C9 * 2 and CYP2C9 * 3 differ in the rate of biotransformation of the corresponding drugs. Thus, in homozygotes CYP2C9 * 2 / * 2 and CYP2C9 * 3 / * 3, the biotransformation of warfarin is reduced to a greater extent than in heterozygotes CYP2C9 * l / * 2 and CYP2C9 * l / * 3. The lowest iotransformational activity is observed in CYP2C9 * 3 / * 3 homozygotes, it is, according to some authors, about 5% of the norm.

Dose, mg / day = [0.628-0.0135x age-0.24xGGR2C5? * 2-0.37xCYP2C9 * 3-0.241xVKORCl + 0.0162xgrowth (cm)] 2

where the CYP2C9 indices are "O", "1" or "2", depending on how many "functionally defective" alleles of this type are present in the patient's genotype, and the VKORC1 indicator, depending on the patient's genotype, according to the haplotype groups of the given locus ( see above) is "1" for genotype BB, "2" for AB, and "3" for AA. This formula was successfully applied in a group of 297 English patients who were prescribed warfarin, with a target MHO of 2.0-3.0 [Sconce Е.А. et al., Blood]. Nevertheless, many authors were skeptical about this attempt to apply a pharmacogenetic approach to the prescription of warfarin. First, the dosing accuracy (the coincidence of the calculated dose with the actually selected one) was, on average, 54%. Secondly, the authors did not divide patients into those who took warfarin for a long time, and those to whom this drug was recently prescribed. Also, all patients significantly differed in the prescribed concomitant therapy.

Dose, mg / day = 6.6-0.035 x age + 0.031 x weight (kg)

This averaged algorithm is intended for patients who do not have “functionally defective” alleles at the CYP2C9 locus in their genotype. In the case of the presence of the CYP2C9 * 2 allele (regardless of whether the patient is homozygous or heterozygous for this allele), the authors propose to reduce the dose calculated according to this algorithm by 1.3 mg.

If the CYP2C9 * 3 allele is present in the patient's genotype, it is proposed to reduce the dose by 2.9 mg [Takahashi et al., 2006]. An obvious disadvantage of this work is the ignorance of the ethnic characteristics of the patients, i.e. the absence in the equation of an argument that takes into account the race of the patient.

American researchers [Hillman et al., 2005] have developed their own method for selecting the dose of warfarin, based on a study of 453 patients with various pathologies. The clinical group for this study was well selected, in particular, pathologies affecting the selection of doses were excluded: malignant tumors, liver and kidney diseases, long-term therapy with barbiturates was excluded. The parameters used in developing the algorithm included: CYP2C9 genotype (CP2C9 * 1 / * 1> CYP2C9 * l / * 2, CYP2C9 * 2 / * 2, CYP2C9 * l / * 3, CYP2C9 * 3 / * 3 and CYP2C9 * 2 / * 3), age, sex, presence of diabetes mellitus and body surface area PPT, calculated by the formula:

PPT = weight 425 x height 725 x 0.007184

For patients with genotype CYP2C9 * 1 / * 1, the average dose of warfarin was 36.5-15.5 mg / week (approximately 5 mg / day), and for homozygotes CYP2C9 * 3 / * 3 - 5.5 mg / week (approximately 1 mg / day) ... As a result, the authors compiled graphs and tables of dose change coefficients, which were proposed as an algorithm for dosing warfarin.

Primers were selected using the "PrimerSelect 4.05" computer program (DNAStar, Inc). The selection was carried out on matrices from the NCBI databank containing the complete sequences of the CYP2C9 and VKORC1 genes, including all exons and introns, reference numbers NC_000010.10 and NC_000016.9, respectively. When selecting primers, we used the conditions set by the authors of the program "by default"; from the primers proposed by the program, we selected those that had the maximum rating, all other things being equal.

Sergey Viktorovich Pushkin thank you for your detailed response. Why would it screen for CYP2C9 gene variants and not VKORC1?

Dear Nori Jan

If you have to investigate the activity of warfarin, then you need to know about those mutations about which I wrote in the previous answer. There are doses in it. For some, due to the production of specific proteins, warfarin practically does not work even in large doses. The CYP2C9 gene triggers protein coding. The CYP2C9 gene encodes the amino acid sequence of the cytochrome 2C9 (C2C9) enzyme. 2C9 is one of the enzymes of the body's detoxification system from xenobiotics; it affects the effectiveness of a number of drugs, especially those used in anticoagulation therapy.

The VKORC1 gene is located on chromosome 16. Encodes the structure of the protein epoxide reductase of vitamin K. This is an enzyme that converts vitamin K from an inactive form (2,3-epoxy vitamin K) to an active form (vitamin K hydroquinolone), which takes part in the carboxylation of vitamin K-dependent blood proteins. Deficiency of vitamin K or vitamin K-dependent blood clotting factors of various origins can lead to bleeding, especially when taking coumarin anticoagulants (they block the enzyme vitamin K epoxide reductase, which, in the presence of mutations in the VKORC1 gene, does not function properly anyway).

These are two important genes that together determine the success / failure of warforin therapy.

Regards, Sergey