CYP2D6 genotyping in a Korean cohort: comparative analysis with Asian, Caucasian, and African populations

Background: Cytochrome P450 2D6 (CYP2D6) is a highly polymorphic enzyme responsible for metabolizing approximately 20% of commonly prescribed drugs. Its genetic variability contributes to interindividual and interethnic differences in drug response. However, large-scale studies on CYP2D6 allele distributions in the Korean population remain limited. Methods: We conducted CYP2D6 genotyping, including copy number variation analysis, in 3,874 unrelated Korean individuals recruited from five university hospitals. Genotypes were assigned diplotypes and phenotypes using the CPIC activity score system. Results: The most frequent allele was the decreased-function *10 (44.9%), followed by normal-function *1 (32.8%) and 2 (11.0%). The gene deletion five accounted for 5.7%. Among phenotypes, 62.2% were extensive metabolizers, 36.1% intermediate metabolizers, 0.9% ultrarapid metabolizers, and 0.4% poor metabolizers. We also identified CYP2D6 × 65, previously unreported in Koreans, and a novel duplication variant, CYP2D6 × 49x2. Conclusion: This is the largest study of CYP2D6 polymorphisms in a Korean population to date. It provides a comprehensive reference for Korean pharmacogenomics and highlights important interethnic differences. The findings support the development of personalized medicine strategies based on population-specific pharmacogenetic data.