Linkage between the distribution of mutations in the CYP2C18 and CYP2C19 genes in the Japanese and Caucasian

1. Two different types of genetic polymorphisms in each of CYP2C18 and CYP2C19 genes were examined and compared with respect to their frequencies in distribution in liver DNA of 39 Japanese and 45 Caucasians. 2. Individuals who were classified into CYP2C19m1 (as detected with SmaI digestion) in exon 5 of CYP2C19 gene were found to display a CYP2C18m1 polymorphism (as detected with DdeI digestion) in the 5-flanking region of CYP2C18 gene in Japanese and Caucasian populations. The Japanese subjects who were classified into CYP2C19m2 (as detected with BamHI digestion) in exon 4 of CYP2C19 gene were found to have a CYP2C18m2 genetic polymorphism (as detected with Tsp509I digestion) in exon 2 of CYP2C18 gene. None of the Caucasians had the CYP2C18m2 nor CYP2C19m2 alleles. 3. Frequencies in two types (C416T in exon 3, A1061C in exon 7) of CYP2C9 genetic polymorphism were found to be independent to those of CYP2C18 and CYP2C19 genetic polymorphisms in these samples. 4. Thus, the results suggest that the CYP2C18 gene is localized very closely to the CYP2C19 gene on the same human chromosome.