WHAT IS KNOWN AND OBJECTIVE

CYP2C1917 allele increases the metabolic activity of CYP2C19 resulting in decreased therapeutic levels of CYP2C19 substrates. There exist inter-ethnic differences in the distribution of this allele. The present study was aimed at establishing the allele and genotype frequencies of CYP2C1917 in a South Indian Tamilian population. Furthermore, we describe the haplotype structure of the three common variant alleles of CYP2C19 in the Tamilian population.

METHODS

Two hundred and six subjects of South Indian Tamilian origin were genotyped for CYP2C1917 allele by nested polymerase chain reaction and restriction fragment length polymorphism. A subset of 87 subjects were also genotyped for CYP2C192 and CYP2C19*3 alleles. After ascertaining linkage disequilibrium (LD), haplotypes were constructed. Allele and genotype frequencies, LD pattern and haplotype frequency were compared with those of the HapMap populations.

RESULTS AND DISCUSSION

The CYP2C1917 allele frequency in the Tamilian population (n = 206) was found to be 19·2% (95% CI: 15·4 - 20·3). The CYP2C192 allele frequency (n = 87) was found to be 40·2% (95% CI: 32·9 - 47·5), whereas the CYP2C193 allele was not detected in the study subjects (n = 97). The high frequency of the CYP2C1917 allele in the study population has resulted in a revision of frequencies for CYP2C19*1/2 (31·0%) and CYP2C191/*1 (16·1%) genotypes in the Tamilian population. We also observed significant differences in haplotype structure and frequencies of these variant alleles in the HapMap population compared to Tamilian population.

WHAT IS NEW AND CONCLUSION

CYP2C1917 allele is present at high frequency in the Tamilian population. This study also demonstrates the need for reassessment of wild-type allele frequencies in view of CYP2C1917 allele. The estimated high frequency of CYP2C19*17 allele will aid in genotype-phenotype association studies in the Tamilian population. Further genotype-phenotype association studies are required to evaluate the clinical utility of this allele in South Indians.