Hiroyuki Hibino

DNA methylation analysis of BDNF gene promoters in peripheral blood cells of schizophrenia patients.

Accumulating evidence suggests that epigenetic alterations in brain-derived neurotrophic factor (BDNF) promoters are associated with the pathophysiology of psychiatric disorders. Epigenetic changes in BDNF were reported not only in brain tissues but also in other tissues, including peripheral blood cells (PBC) and saliva. We examined DNA methylation levels of BDNF promoters I and IV using genomic DNA derived from PBC of healthy controls (n=100), and patients with schizophrenia (n=100), all from the Japanese population, by pyrosequencing. The examined CpG sites were chosen based on previous epigenetic studies that reported altered DNA methylation. We found a significantly higher level of methylation at BDNF promoter I in patients with schizophrenia compared to controls, although the difference was small. Subsequent analysis revealed that in controls, the methylation level of BDNF promoters was associated with sex, and the methylation difference observed in promoter I was more prominent in male patients with schizophrenia. Epigenetic alteration of BDNF in the PBC might reflect the pathophysiology of schizophrenia, and could be a potential biomarker.

Combined analysis of association between personality traits and three functional polymorphisms in the tyrosine hydroxylase, monoamine oxidase A, and catechol-O-methyltransferase genes

Several molecular genetic studies have been conducted with regard to the association between catecholamine-related genes and personality traits. However, the results of replication studies did not always coincide. One of the possible reasons may be that the effect exerted by the individual gene is small. In the present study, we investigated the association between personality traits and systematic combination of functional polymorphisms in three genes that regulate the metabolism of catecholamines, namely, tyrosine hydroxylase (TH), monoamine oxidase A (MAOA), and catechol-O-methyltransferase (COMT). The (TCAT)n repeat in the TH gene, the promoter variable number tandem repeat (VNTR) in the MAOA gene, and Val158Met in the COMT gene were genotyped in 256 healthy Japanese volunteers. Personality traits were evaluated using the NEO Personality Inventory-Revised (NEO PI-R). As a result, the score for Neuroticism increased, and those for Extraversion and Conscientiousness decreased according to the degree of functional polymorphic change, i.e., the lower synthesis/higher catalysis of catecholamines. A statistically significant difference was observed in the change of Extraversion (p=0.04, after Bonferroni correction). These results may provide evidence for the association between metabolic change of catecholamines and personality traits, which may be due to the additive effect of the three genes.

Association study of the dysbindin (DTNBP1) gene in schizophrenia from the Japanese population.

Dysbindin (DTNBP1: dystrobrevin binding protein 1), located on 6p22.3, is a candidate susceptibility gene for schizophrenia. Several studies, mostly in Caucasians, have provided evidence for an association between schizophrenia and the gene, although no common polymorphism or haploytpe has been established. In Asian populations, two studies investigated a limited number of single nucleotide polymorphisms (SNPs) of dysbindin and observed support for the association. In the present study, we investigated 12 SNPs of dysbindin, including those examined in previous Asian studies, and the corresponding haplotypes in a Japanese people with schizophrenia. As a result, no significant difference was observed between patients and controls in allelic frequencies or genotypic distributions of the 12 SNPs. Permutation test however showed significant differences in frequencies of the estimated 10-marker haplotypes between patients and controls (global p = 0.006). The present study may provide further support for an association between dysbindin and schizophrenia in Asian populations. The results might be similar to a previous Asian study, but specific haplotypes suggested for the association differed between the studies. Studies with more markers and subjects may be required before firm conclusions can be reached.

Association between dopamine D4 receptor (DRD4) exon III polymorphism and Neuroticism in the Japanese population

The association between the dopamine D4 receptor (DRD4) exon III polymorphism and personality trait of novelty seeking (NS) has been studied intensively. In the Japanese population, the results of the previous studies did not always coincide. In the present study, we investigated the association between the polymorphism and personality traits evaluated by using the Revised NEO Personality Inventory (NEO PI-R) and State-Trait Anxiety Inventory (STAI) in 196 Japanese subjects. A meta-analysis of the present and previous Japanese studies was also conducted regarding NS. As a result, significant association was observed between the polymorphism and personality traits evaluated by using NEO PI-R as a whole (p=0.022, MANCOVA). Subsequent analyses showed a significant association between short alleles (2-4 repeats) and higher scores for Neuroticism or its subscales, Anxiety, Depression, and Vulnerability (p=0.015, 0.039, 0.021, and 0.008, respectively, uncorrected). No other significant difference in the scores for NEO PI-R was observed in the subsequent analyses. Significant association was also observed between the polymorphism and scores for STAI as a whole (p=0.004, MANCOVA). Subsequent analyses did not show significant association, although a weak trend for the relation between the genotype consisting of short alleles and Trait Anxiety was observed (p=0.10, uncorrected). The meta-analysis showed no significant association between the polymorphism and NS. Thus, the present study suggested the association between the short allele of the DRD4 exon III polymorphism and personality trait of Neuroticism in Japanese subjects.

Association study of monoamine oxidase and catechol-O-methyltransferase genes with smoking behavior.

Objective The genes of catalytic enzymes of dopamine, including monoamine oxidase (MAOA and MAOB) and catechol-O-methyltransferase (COMT), have been major candidates for genes that affect smoking behavior. In this study, we investigated the relationship between smoking behavior and four polymorphisms of these genes, the MAOA variable number tandem repeat polymorphism, the MAOA 1460 T/C polymorphism, the MAOB intron 13 G/A polymorphism, and the COMT Val158Met polymorphism. The association between the MAOB polymorphism and personality traits was also explored. Participants and methods The polymorphisms were genotyped in 451 healthy Japanese volunteers. Data on smoking habits were obtained from structured interviews. In addition to testing the association between each polymorphism and smoking status, epistatic and additive effects between two polymorphisms were also investigated. Results A significant association was observed between the COMT Val158Met polymorphism and smoking status. Male participants with the Val/Val genotype had a significantly higher risk of heavy smoking compared with those with other genotypes, although no significant association was observed in female participants. No evidence was obtained for an association between the MAO genes and smoking behavior, including epistatic or additive effects. No significant association was observed between the MAOB polymorphism and personality traits. Conclusion This study may suggest a role of the COMT Val158Met polymorphism in smoking behavior in Japanese individuals.

Serotonin transporter-linked promoter region polymorphism and personality traits in a Japanese population

Serotonin transporter gene may play a critical role in a regulation of mood and other aspects of mental status. A large number of association studies have investigated a correlation between the polymorphism in the serotonin transporter-linked promoter region (5-HTTLPR) and anxiety-related personality traits. The results, however, have been inconsistent. Heterogeneity of subjects regarding gender, occupation, social-class and other environmental factors, in addition to effects of other genes, might have confounded the results. Here, we studied an association between the 5-HTTLPR polymorphism and personality traits in primarily female (78%) healthy subjects (n=244), who had homogeneous backgrounds regarding ethnicity (Japanese) and occupation. Personality traits of the subjects were assessed with the revised NEO Personality Inventory. No significant association was observed between the polymorphism and neuroticism or other personality traits, in all subjects, all females (n=190) or female nurses (n=159). Thus, our findings provided no evidence for an association between the 5-HTTLPR polymorphism and anxiety-related or other personality traits.

Mitochondrial DNA polymorphisms and extraversion

Mitochondria is the major site of energy production in cells, therefore, mitochondrial abnormality may affect functions of organs including the brain, which constantly requires high levels of energy consumption. Previous studies have suggested a role of mitochondria and their DNA polymorphisms in neuro‐psychiatric disorders, including Alzheimers disease, Parkinsons disease, schizophrenia and bipolar mood disorder. Thus, we hypothesized that mitochondrial DNA polymorphisms might be related with the development of personality. The present study investigated a role of two mitochondrial DNA polymorphisms, the C5178A and A10398G, in personality traits evaluated using the NEO PI‐R scores in 238 healthy Japanese volunteers. Subjects with the 5178A genotype showed significantly higher extraversion score than those with the 5178C genotype (P = 0.027), while no significant association was observed between the C5178A polymorphism and other scores. No significant association was found between the A10398G polymorphism and any scores. Regarding the 5178–10398 haplotype, the score of extraversion, not other scores, was significantly associated with the A–G haplotype (P = 0.042). Although further studies are recommended for the confirmation, the result may suggest a role of the mitochondrial DNA polymorphism in the personality trait.

Serotonin 2A receptor gene polymorphism and personality traits: no evidence for significant association.

A number of studies have observed associations between the serotonin 2A (5-HT2A) receptor and mental disorders. Here, we investigated correlations between polymorphisms (−1438G/A and 102T/C) of the 5-HT2A gene and personality traits in healthy Japanese volunteers (n=239). The personality traits were evaluated using the Revised NEO Personality Inventory (NEO PI-R). The −1438G/A and 102T/C were in complete linkage disequilibrium. There was a tendency for associations between the genotype and the scores for Agreeableness, Conscientiousness and Neuroticism of the NEO PI-R (P=0.028, 0.039 and 0.062, respectively; analysis of variance, uncorrected for multiple testing). Subjects with the A/A of −1438G/A (or T/T of 102T/C) appeared to be lower in Neuroticism and higher in Conscientiousness than the rest of the subjects. However, the results were statistically non-significant after Bonferronis correction for multiple testing of the five scales of the NEO PI-R. Thus, the present study provided no evidence for statistically significant associations between the 5-HT2A polymorphisms and the personality traits.

Association study between the TNXB locus and schizophrenia in a Japanese population

The chromosome 6p21–24 region, which contains the human leukocyte antigen (HLA) region, has been suggested as an important locus for a susceptibility gene for schizophrenia. Recently, a significant association between schizophrenia and the TNXB locus, located immediately telomeric of the NOTCH4 locus in the HLA region, was observed. Few studies have further investigated the region in schizophrenia. In the present study, we investigated the region in a Japanese population. Subjects included 241 patients with schizophrenia and 290 controls. Twenty‐six single nucleotide polymorphisms (SNPs) and the corresponding haplotypes were analyzed. As a result, exactly the same SNPs in the TNXB locus (rs1009382 and rs204887) as in the previous study were associated with schizophrenia (P = 0.034 and 0.034, respectively, uncorrected). A SNP (rs2071287) in the NOTCH4 locus and haplotype around it were also suggested to associate with the disease, consistent with another previous study (P = 0.041 and permutation P = 0.024, respectively, uncorrected). Although these associations became insignificant after Bonferroni correction, the findings might provide support for the association of the TNXB locus or its adjacent region of the NOTCH4 locus with schizophrenia.

Human leukocyte antigen-A specificities and its relation with season of birth in Japanese patients with schizophrenia

Several studies, including one from Japan, have observed an increase of Human Leukocyte Antigen (HLA)-A24 and A26 in schizophrenia, although others failed to observe the increase. No use of systematic diagnostic criteria and a not-adequately reliable typing technique might have affected the results in the previous studies. We investigated HLA-A specificities in Japanese patients with schizophrenia (DSM-IV), recruited from the same area as in the early Japanese study. A DNA-based technique (polymerase chain reaction-microtiter plate hybridization) was employed. No significant difference was observed in frequencies of any HLA-A specificities between patients and controls, including A24 and A26. No significant association was found between the HLA-A and birth-season in patients. Thus, no evidence was obtained for an association between HLA-A and schizophrenia from the Japanese population.