Frequencies of CYP2D6 mutant alleles in a normal Japanese population and metabolic activity of dextromethorphan
O‐demethylation in different CYP2D6 genotypes

AIMS: To determine the frequencies of 11 CYP2D6 mutant alleles (CYP2D6*2, *3, *4, *5, *8, *10, *11, *12, *14, *17 and *18), and their relation to the metabolic capacity of CYP2D6 in Japanese subjects. METHODS: One hundred and sixty-two unrelated healthy Japanese subjects were genotyped with the polymerase chain reaction amplification method and 35 subjects were phenotyped with dextromethorphan. RESULTS: The frequencies of CYP2D6*2,*5, *10 and *14 were 12.9, 6.2, 38.6 and 2.2% in our Japanese subjects, respectively. CYP2D6*3, *4, *8, *11, *12, *17 and *18 were not detected. The mean log metabolic ratio of dextromethorphan in subjects with genotypes predicting intermediate metabolizers was significantly greater than that of heterozygotes for functional and defective alleles. CONCLUSIONS: CYP2D6*5 and CYP2D6*14 are the major defective alleles found in Japanese subjects. In addition, CYP2D6*10 may play a more important role than previously thought for the treatment of Japanese patients with drugs metabolized by CYP2D6.