The effect of the CYP 2C19*2 polymorphism on stroke care

Clopidogrel is an inhibitor of platelet-aggregation used in the prevention of secondary stroke. The molecule is activated by the cytochrome P450 2C19 (CYP2C19) enzyme. The frequent CYP2C19*2 point mutation causes loss of enzyme function, a decreased (heterozygous form) or blocked (homozygous form) formation of the active molecule. Thus, for a patient harboring a mutated allele, clopidogrel does not provide effective protection against stroke. Multiple drugs inhibit the CYP2C19 enzyme and their simultaneous use with clopidogrel is especially hazardous for patients with genetically decreased enzyme activity. Frequency of the CYP2C19*2 is variable in different populations, highest rates were detected in some Asian groups. In our study the CYP2C19 genotype was determined in one Hungarian sample of 354 stroke patients and 221 healthy controls. Frequency of the minor allele was found to be 12.87% (12.85% in stroke patients, 12.89% in healthy controls). The proportion of the homozygous CYP2C19*2 variant causing total loss of gene function was 1.74%, rate of the heterozygous allele causing reduced enzyme activity was 22.26% in the total population. Our results for the allele frequencies of the CYP2C19*2 gene are similar to those found in other Caucasian populations. In conclusion, the homozygous mutation, causing ineffectiveness of clopidogrel is relatively rare. However, the heterozygous form in which interaction of CYP2C19 inhibitors causes further decrease in the genetically impaired enzyme activity is present in every fifth drug-taking patient. Based on our findings, we would like to emphasize that it is important to adjust individually antiplatelet treatment in ischemic stroke patients and to take into consideration genetic factors as well as drugs taken for comorbid conditions.