Yoshihito Ito

Genome-wide association study of schizophrenia in a Japanese population.

BACKGROUND Genome-wide association studies have detected a small number of weak but strongly supported schizophrenia risk alleles. Moreover, a substantial polygenic component to the disorder consisting of a large number of such alleles has been reported by the International Schizophrenia Consortium. METHOD We report a Japanese genome-wide association study of schizophrenia comprising 575 cases and 564 controls. We attempted to replicate 97 markers, representing a nonredundant panel of markers derived mainly from the top 150 findings, in up to three data sets totaling 1990 cases and 5389 controls. We then attempted to replicate the observation of a polygenic component to the disorder in the Japanese and to determine whether this overlaps that seen in UK populations. RESULTS Single-locus analysis did not reveal genome-wide support for any locus in the genome-wide association study sample (best p = 6.2 × 10(-6)) or in the complete data set in which the best supported locus was SULT6B1 (rs11895771: p = 3.7 × 10(-5) in the meta-analysis). Of loci previously supported by genome-wide association studies, we obtained in the Japanese support for NOTCH4 (rs2071287: p(meta) = 5.1 × 10(-5)). Using the approach reported by the International Schizophrenia Consortium, we replicated the observation of a polygenic component to schizophrenia within the Japanese population (p = .005). Our trans Japan-UK analysis of schizophrenia also revealed a significant correlation (best p = 7.0 × 10(-5)) in the polygenic component across populations. CONCLUSIONS These results indicate a shared polygenic risk of schizophrenia between Japanese and Caucasian samples, although we did not detect unequivocal evidence for a novel susceptibility gene for schizophrenia.

Resequencing and Association Analysis of the KALRN and EPHB1 Genes And Their Contribution to Schizophrenia Susceptibility

BACKGROUND Our genome-wide association study of schizophrenia found association signals at the Kalirin gene (KALRN) and EPH receptor B1 gene (EPHB1) in a Japanese population. The importance of these synaptogenic pathway genes in schizophrenia is gaining independent supports. Although there has been growing interest in rare (<1%) missense mutations as potential contributors to the unexplained heritability of schizophrenia, there are no population-based studies targeting rare (<1%) coding mutations with a larger effect size (eg, OR >1.5) in KALRN or EPHB1. METHODS AND RESULTS The present study design consisted of 3 phases. At the discovery phase, we conducted resequencing analyses for all exon regions of KALRN and EPHB1 using a DNA microarray-based method. Seventeen rare (<1%) missense mutations were discovered in the first sample set (320 schizophrenic patients). After the prioritization phase based on frequencies in the second sample set (729 cases and 562 controls), we performed association analyses for each selected mutation using the third sample set (1511 cases and 1517 controls), along with a combined association analysis across all selected mutations. In KALRN, we detected a significant association between schizophrenia and P2255T (OR = 2.09, corrected P = .048, 1 tailed); this was supported in the combined association analysis (OR = 2.07, corrected P = .006, 1 tailed). We found no evidence of association of EPHB1 with schizophrenia. In silico analysis indicated the functional relevance of these rare missense mutations. CONCLUSION We provide evidence that multiple rare (<1%) missense mutations in KALRN may be genetic risk factors for schizophrenia.

Gene-wide association study between the methylenetetrahydrofolate reductase gene (MTHFR) and schizophrenia in the Japanese population, with an updated meta-analysis on currently available data

Methylenetetrahydrofolate reductase (MTHFR) is a critical molecule for single-carbon transfer reactions. Recent evidence suggests that polymorphisms of MTHFR are related to neural tube deficits and the pathogenesis of schizophrenia. While several studies have demonstrated associations between the gene encoding the MTHFR (MTHFR) polymorphisms and schizophrenia, these studies lack consistency. Therefore, we conducted a gene-wide association study (patients with schizophrenia = 696, control subjects = 747) and performed imputation analysis. Additionally, we performed meta-analysis on currently available data from 18 studies for two common functional polymorphisms (rs1801131 and rs1801133). There were no significant associations with schizophrenia in the single marker analysis for the seven tagging SNPs of MTHFR. In the haplotypic analysis, a nominally significant association was observed between the haplotypes, which included four SNPs (rs1801133, rs17421511, rs17037396, and rs9651118) and the schizophrenic patients. Additionally, the imputation analysis demonstrated there were several associated markers on the MTHFR chromosomal region. However, confirmatory analyses of three tagging SNPs (rs1801133, rs17037396, and rs9651118) and the top SNP (rs17421511) for the imputation results (patients with schizophrenia = 797, control subjects = 1025) failed to replicate the haplotypic analysis and the imputation results. These findings suggest that MTHFR polymorphisms are unlikely to be related to the development of schizophrenia in the Japanese population. However, since our meta-analysis results demonstrated strong support for association of rs1801133 with schizophrenia, further replication studies based on a gene-wide approach need to be considered.

Genetic analysis of the gene coding for DARPP-32 (PPP1R1B) in Japanese patients with schizophrenia or bipolar disorder

Several lines of evidence, including genome-wide linkage scans and postmortem brain studies of patients with schizophrenia or bipolar disorder, have suggested that DARPP-32 (dopamine- and cAMP-regulated phosphoprotein, 32 kDa), a key regulatory molecule in the dopaminergic signaling pathway, is involved in these disorders. After evaluating the linkage disequilibrium pattern of the gene encoding DARPP-32 (PPP1R1B; located on 17q12), we conducted association analyses of this gene with schizophrenia and bipolar disorder. Single-marker and haplotypic analyses of four single nucleotide polymorphisms (SNPs; rs879606, rs12601930, rs907094, and rs3764352) in a sample set (subjects with schizophrenia=384, subjects with bipolar disorder=318, control subjects=384) showed that PPP1R1B polymorphisms were not significantly associated with schizophrenia, whereas, even after Bonferroni corrections, significant associations with bipolar disorder were observed for rs12601930 (corrected genotypic p=0.00059) and rs907094 (corrected allelic p=0.040). We, however, could not confirm these results in a second independent sample set (subjects with bipolar disorder=366, control subjects=370). We now believe that the significant association observed with the first sample set was a result of copy number aberrations in the region surrounding these SNPs. Our findings suggest that PPP1R1B SNPs are unlikely to be related to the development of schizophrenia and bipolar disorder in the Japanese population.

Genetic association study of KREMEN1 and DKK1 and schizophrenia in a Japanese population.

The aim of the current study was to examine the association of KREMEN1 and DKK1, two wnt pathway-related genes with schizophrenia in Japanese subjects. We genotyped 16 common genetic variants within the aforementioned genes and examined their associations with schizophrenia. Results demonstrated that a common variant in the promoter region of KREMEN1 might modulate the risk of schizophrenia in the Japanese. However, further replication will be needed for conclusive interpretation of the effect of this locus on the pathogenesis of schizophrenia.

Influence of HTR2A polymorphisms and parental rearing on personality traits in healthy Japanese subjects

Genetic factors and environmental influences contribute to the determination of human personality traits. This study examined the influence of serotonin receptor 2A polymorphisms and parental rearing on temperament. Subjects included 1245 Japanese volunteers (592 males and 653 females). Three single-nucleotide polymorphisms (SNPs) (rs6311, rs6313 and rs643627) were selected for genotyping. All subjects completed the 125-item Japanese short version of the temperament and character inventory, and 572 completed the Japanese version of the Parental Bonding Instrument. All SNPs were in Hardy–Weinberg equilibrium. A significant association (P=0.0026) was observed between rs643627 and novelty seeking in females. On the other hand, significant effects of maternal overprotection to harm avoidance (HA) were seen for rs6311 (P=0.0005), rs6313 (P=0.0004) and rs643627 (P=0.0003) in males only. In terms of the interaction of genotype and maternal overprotection with HA, interaction was observed in rs6311 (P=0.0290) and rs6313 (P=0.0230) in females only. Our results indicate a relationship between the rs643627 polymorphism and novelty seeking in females. In terms of serotonin receptor 2A gene polymorphisms and maternal overprotection, our findings suggest the existence of a gene–environmental interaction that influences HA.

Analysis of the VAV3 as Candidate Gene for Schizophrenia: Evidences From Voxel-Based Morphometry and Mutation Screening

In recently completed Japanese genome-wide association studies (GWAS) of schizophrenia (JPN_GWAS) one of the top association signals was detected in the region of VAV3, a gene that maps to the chromosome 1p13.3. In order to complement JPN_GWAS findings, we tested the association of rs1410403 with brain structure in healthy individuals and schizophrenic patients and performed exon resequencing of VAV3. We performed voxel-based morphometry (VBM) and mutation screening of VAV3. Four independent samples were used in the present study: (1) for VBM analysis, we used case-control sample comprising 100 patients with schizophrenia and 264 healthy controls, (2) mutation analysis was performed on a total of 321 patients suffering from schizophrenia, and 2 case-control samples (3) 729 unrelated patients with schizophrenia and 564 healthy comparison subjects, and (4) sample comprising 1511 cases and 1517 healthy comparison subjects and were used for genetic association analysis of novel coding variants with schizophrenia. The VBM analysis suggests that rs1410403 might affect the volume of the left superior and middle temporal gyri (P=.011 and P=.013, respectively), which were reduced in patients with schizophrenia compared with healthy subjects. Moreover, 4 rare novel missense variants were detected. The mutations were followed-up in large independent sample, and one of the novel variants (Glu741Gly) was associated with schizophrenia (P=.02). These findings demonstrate that VAV3 can be seen as novel candidate gene for schizophrenia in which both rare and common variants may be related to increased genetic risk for schizophrenia in Japanese population.

The expression of HMGA1a is increased in lymphoblastoid cell lines from schizophrenia patients

The high-mobility group A protein 1a (HMGA1a) is a well-documented DNA-binding protein acting as an architectural transcription regulator. Recently, HMGA1a protein has been identified as a hypoxia-inducible RNA-binding trans-acting factor for aberrant splicing of presenilin-2 (PS2) pre-mRNA observed in the brains of sporadic Alzheimers disease. Interestingly, this aberrant splicing of PS2 was also observed in the brains of bipolar disorder and schizophrenia. Many downstream genes under the control of HMGA1a could be associated with schizophrenia. On the other hand, many gene transcripts are aberrantly spliced in schizophrenia. Therefore, we examined the expression at the mRNA and protein levels of this DNA- and RNA-binding factor HMGA1a in the lymphoblastoid cell lines obtained from 16 schizophrenia patients with age-matched controls. We observed markedly higher HMGA1a mRNA and the increased HMGA1a protein in the nuclear fractions of schizophrenia patients. In contrast, there were no significant differences in the expression levels of HMGA1b, which is an alternatively spliced isoform of HMGA1a. The present study is the first to report a significant upregulation of HMGA1a in schizophrenia, suggesting its potential roles in both transcription and splicing of target genes linked with schizophrenia.

Association study of ubiquitin-specific peptidase 46 (USP46) with bipolar disorder and schizophrenia in a Japanese population

Recently, ubiquitin-specific peptidase 46 (Usp46) has been identified as a quantitative trait gene responsible for immobility in the tail suspension test and forced swimming test in mice. Mice with 3-bp deletion in Usp46 exhibited loss of ‘behavioral despair’ under inescapable stresses in addition to abnormalities in circadian behavioral rhythms and the GABAergic system. Considering the face and construct validity as an animal model for bipolar disorder, we explored an association of USP46 and bipolar disorder in a Japanese population. We also examined an association of USP46 and schizophrenia. We found nominal evidence for an association of rs12646800 and schizophrenia. This association was not significant after correction for multiple testing. No significant association was detected for bipolar disorder. In conclusion, our data argue against the presence of any strong genetic susceptibility factors for bipolar disorder or schizophrenia in the region USP46.

No association between the protein tyrosine phosphatase, receptor‐type, Z Polypeptide 1 (PTPRZ1) gene and schizophrenia in the Japanese population

NRG1‐ERBB signaling influences the risk for schizophrenia pathology. A recent study has reported that MAGI1, MAGI2, and protein tyrosine phosphatase, receptor‐type, Z polypeptide 1 (PTPRZ1; located on 7q31.3) gene products regulate the NRG1‐ERBB4 signaling pathway, and PTPRZ1 is associated with schizophrenia in a Caucasian population. By applying a gene‐based association concept, we analyzed any association between PTPRZ1 tagging SNPs and schizophrenia in the Japanese population (576 schizophrenics and 768 controls). After linkage disequilibrium analysis, 29 single nucleotide polymorphisms (SNPs) were genotyped using a 5′‐exonuclease allelic discrimination assay. We found a significant association of one tagging SNP in a genotype‐wise analysis (P = 0.007); however, this might be resulted from type I error due to multiple testing (P = 0.17 after SNPSpD correction). No association was observed between schizophrenic patients and controls in either allelic, genotypic, or haplotypic analyses. Our results therefore suggest that PTPRZ1 is unlikely to be related to the development of schizophrenia in the Japanese population.