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Objective It has been suggested that cytochrome P450 2D6 (CYP2D6) is involved in dopamine metabolism within the brain. The dopamine system is suggested to play a role in determining normal character. The purpose of this study was to examine whether character traits are dependent on cytochrome P450 2D6 activity. Methods We investigated the association between temperament and CYP2D6 gene polymorphism. The subjects were all Japanese and the polymorphism genotyped in the present study was CYP2D6*10. Character traits were assessed using the Temperament and Character Inventory. Results There was no overall or specific association between personality traits and the CYP2D6*10 allele and genotype frequencies. Conclusions The present results do not support the hypothesis that CYP2D6 activity affects temperament and character.

Objective The purpose of this study was to examine whether the neuroleptic-induced extrapyramidal symptoms are associated with the CYP2D6 activity. Methods The CYP2D6 gene polymorphisms (CYP2D6*2, CYP2D6*3, CYP2D6*4, CYP2D6*10, and CYP2D6*12) were genotyped in 196 normal controls and 320 schizophrenic patients receiving neuroleptics. The relationships with susceptibility to extrapyramidal symptoms (EPS) and tardive dyskinesia, and with steady-state serum haloperidol levels in maintenance therapy, were investigated. Results The allele frequency of CYP2D6*2 was significantly higher, while that of CYP2D6*10 tended to be higher in the schizophrenic patients susceptible to acute EPS. The steady-state serum haloperidol levels per daily dosage were observed to be significantly higher in schizophrenic patients with the mutant-type homozygote of CYP2D6*2, while this difference was trend level in those of CYP2D6*10. However, no significant difference was observed in the distribution of both CYP2D6*2 (C2938T) and CYP2D6*10 (C188T) polymorphisms between schizophrenic patients with or without tardive dyskinesia. Conclusion The present results suggest that the homozygotes of CYP2D6*2 and CYP2D6*10 appear to be a susceptibility factor for developing acute EPS in schizophrenic patients and for impaired neuroleptic metabolism in Japanese schizophrenic patients.