Allele frequency distribution of CYP2C19*2 allelic variants associated with clopidogrel resistance in cardiac patients.

Drug resistance is a phenomenon that has become a critical issue in medical practice. Such is the case in the response to clopidogrel treatment, which is variable inter-individually and inter-ethnically due to genetic polymorphisms in the cytochrome P40 (CYP) gene. Clopidogrel is an anti-platelet agent administered to cardiac patients in the form of a prodrug, which is further metabolized into an active form by CYP enzymes. There are many allelic variants of the CYP gene that are involved in clopidogrel resistance, of which CYP2C19*2 has been demonstrated to be one of the most significant loss-of-function alleles. In the present study, 100 cardiac patients with percutaneous coronary intervention (PCI) or acute coronary syndrome (ACS) who were undergoing treatment with clopidogrel were selected and the patients were analyzed for CYP2C19*2 allelic variants using an allele-specific primer extension polymerase chain reaction method. The variant amplicons were visualized on gel and validated by Sanger sequencing. The observed allelic frequency distribution of CYP2C19*2 variants was 18% heterozygous for CYP2C19*2 A/C/G variants, 35% heterozygous for A/G variants, 13% heterozygous for C/G variants, 6% heterozygous for A/C variants, 7% homozygous for A variant, 5% homozygous for C variant and 16% homozygous for G wild-type. Furthermore, tri-allelic single nucleotide polymorphisms (SNPs) were identified in the CYP2C19*2 allele in cardiac patients for the first time, to the best of our knowledge; these were CYP2C19*2 A/C/G SNPs (18%). The overall frequency observed for new allelic variant C of CYP2C19*2 was 42%. These results suggested that there are significant inter-ethnic variations in the allelic frequencies of CYP2C19*2, which may be responsible for the variable clopidogrel response in cardiac patients.