Low frequency of defective alleles of cytochrome P450 enzymes 2C19 and 2D6 in the Turkish population

Background and Objectives The genetically polymorphic cytochrome P450 enzymes 2C19 (CYP2C19) and 2D6 (CYP2D6) contribute to the metabolism of about 30% of all drugs. For analysis of the ethnic‐related differences in drug disposition and as a preparation for routine genotyping, we examined CYP2C19 and CYP2D6 mutations in a large Turkish population. Methods Cyp2C19 and CYP2D6 alleles were determined with use of genomic deoxyribonucleic acid from 404 unrelated Turkish individuals. CYP2C19 alleles *1 to *5 and CYP2D6 alleles *1 to *12 , and *14, *15 , and *17 were measured by polymerase chain reaction–restriction fragment length polymorphism assays. Results From 404 subjects genotyped for CYP2C19 , allele frequencies of CYP2C19*1 (wt), CYP2C19*2 (m1), and CYP2C19*3 (m2) were 0.88, 0.12, and 0.004, respectively; mutations m3 and m4 were not found. Four individuals (1.0%) were predicted to be poor metabolizers ( CYP2C19*2/*2 ), a significantly lower frequency compared to Middle European populations. Among 404 subjects genotyped for CYP2D6 , most frequent alleles were CYP2D6*1 (allele frequency 0.37), *2 (0.35), *4 (0.11), *10 (0.06), duplications *1×2, *2×2 , or *4×2 (0.06), *5 (0.01), and *17 (0.01). Overall, six subjects (1.49%) were predicted to be CYP2D6 poor metabolizers, and 35 subjects (8.66%) were predicted to be ultrarapid metabolizers as a result of CYP2D6 gene duplications. Conclusion Obviously, within Europe there is a north‐south gradient, with decreasing frequency of poor metabolizers of CYP2C19 and CYP2D6 to the south and a corresponding increase of ultrarapid metabolizers of CYP2D6. As in other white groups, only CYP2C19*2 plays a relevant role for the CYP2C19 poor metabolizer phenotype. The mutational spectrum of CYP2D6 indicated partial ethnic relationships to Asian and African populations. Clinical Pharmacology & Therapeutics (1999) 66 , 185–192; doi: 10.1053/cp.1999.v66.100072001