Kew word.s : The cytochrome P-4-50-dependent monooxygenasc system is involvcd in the metabolism of both endogeiious compounds and xenobiotics. 'l'he role of these enzymes in toxicological response is exemplified by an autosomal rccessive polymorphism at the cytochrome PJ450 2D6 debrisoquine-4・-hydroxylase locus, which rcsults in thc severely impaired metabolism of many drugs [Gough et al. <1990) Nature S47: 773-7761. The prevalcnce of this polymorphism <poor metabelizer) ditTttrs consiclerably

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... etween ethnic groups. Here we analyzed the P-450 2D6 polymorphism in 25 Japanese and 20 Chinese by DNA-based genetic assay using peripheral lcukocyte, AItheugh the phenotype ot' all the normal metabolizers and 79% of the poor mctabolizers could be iclcntified in Caucasians, this DNA-based genomic assa}, couid not predict poor metabolizers in both the Japanese and Chinese. These results indicate that the genetic mechanism of the phenetypcd poor mctabolizer in Orientals is ditlbrcnt from that in Caucasians. c)ptochrome P-450 2D6, debrisoquine 4-hydroxylation, cthnic diffbrcnce.