Tsuyoshi Kitajima

Association of AKT1 with schizophrenia confirmed in a Japanese population

BACKGROUND Abnormality of the V-akt murine thymoma viral oncogene homologue 1 (AKT1) may be a predisposing factor in schizophrenia. Recent evidence supporting this hypothesis showed decreased AKT1 protein levels in patients with schizophrenia and significant association of AKT1 haplotypes according to the transmission disequilibrium test. METHODS We provide the first replication of this evidence using a relatively large case-control sample (507 Japanese schizophrenia and 437 control subjects). We genotyped five single nucleotide polymorphisms (SNPs) from the original study and one additional SNP. RESULTS We found a positive association with an SNP (SNP5) different from the original studys findings (SNP3) and also significance in the haplotypes constructed from the combination of SNP5. Linkage disequilibrium around SNP5 was complex and may produce this positive association. CONCLUSIONS Our study provides support for the theory that AKT1 is a susceptibility gene for Japanese schizophrenia. Fine linkage disequilibrium mapping is required for a conclusive result.

A Missense Variation in Human Casein Kinase I Epsilon Gene that Induces Functional Alteration and Shows an Inverse Association with Circadian Rhythm Sleep Disorders

Recent studies have shown that functional variations in clock genes, which generate circadian rhythms through interactive positive/negative feedback loops, contribute to the development of circadian rhythm sleep disorders in humans. Another potential candidate for rhythm disorder susceptibility is casein kinase I epsilon (CKIɛ), which phosphorylates clock proteins and plays a pivotal role in the circadian clock. To determine whether variations in CKIɛ induce vulnerability to human circadian rhythm sleep disorders, such as delayed sleep phase syndrome (DSPS) and non-24-h sleep–wake syndrome (N-24), we analyzed all of the coding exons of the human CKIɛ gene. One of the variants identified encoded an amino-acid substitution S408N, eliminating one of the putative autophosphorylation sites in the carboxyl-terminal extension of CKIɛ. The N408 allele was less common in both DSPS (p=0.028) and N-24 patients (p=0.035) compared to controls. When DSPS and N-24 subjects were combined, based on an a priori prediction of a common mechanism underlying both DSPS and N-24, the inverse association between the N408 allele and rhythm disorders was highly significant (p=0.0067, odds ratio=0.42, 95% confidence interval: 0.22–0.79). In vitro kinase assay revealed that CKIɛ with the S408N variation was ∼1.8-fold more active than wild-type CKIɛ. These results indicate that the N408 allele in CKIɛ plays a protective role in the development of DSPS and N-24 through alteration of the enzyme activity.

Copy Number Variation in Schizophrenia in the Japanese Population

BACKGROUND Copy number variants (CNVs) have been shown to increase the risk to develop schizophrenia. The best supported findings are at 1q21.1, 15q11.2, 15q13.3, and 22q11.2 and deletions at the gene neurexin 1 (NRXN1). METHODS In this study, we used Affymetrix 5.0 arrays to investigate the role of rare CNVs in 575 patients with schizophrenia and 564 control subjects from Japan. RESULTS There was a nonsignificant trend for excess of rare CNVs in schizophrenia (p = .087); however, we did not confirm the previously implicated association for very large CNVs (>500 kilobase [kb]) in this population. We provide support for three previous findings in schizophrenia, as we identified one deletion in a case at 1q21.1, one deletion within NRXN1, and four duplications in cases and one in a control subject at 16p13.1, a locus first implicated in autism and later in schizophrenia. CONCLUSIONS In this population, we support some of the previous findings in schizophrenia but could not find an increased burden of very large (>500 kb) CNVs, which was proposed recently. However, we provide support for the role of CNVs at 16p13.1, 1q21.1, and NRXN1.

Variants of dopamine and serotonin candidate genes as predictors of response to risperidone treatment in first-episode schizophrenia.

AIMS Abnormalities in dopaminergic and serotonergic transmission systems are thought to be involved in the pathophysiology of schizophrenia and the mechanisms underlying the therapeutic effects of antipsychotics. We conducted a pharmacogenetic study to evaluate whether variants in dopamine-related genes (DRD1-DRD5, AKT1 and GSK3beta) and serotonin receptor genes (HTR1A, HTR1B, HTR1D, HTR2A, HTR2C, HTR6 and HTR7) can be used to predict the efficacy of risperidone treatment for schizophrenia. MATERIALS & METHODS A total of 120 first-episode neuroleptic-naive schizophrenia patients were treated with risperidone monotherapy for 8 weeks and clinical symptoms were evaluated by the Positive and Negative Syndrome Scale. RESULTS Among the 30 variants that we examined, two SNPs in DRD2 (-241A>G [rs1799978] and TaqIA [rs1800497]) and two SNPs in AKT1 (AKT1-SNP1 [rs3803300] and AKT1-SNP5 [rs2494732]) were significant predictors of treatment response to risperidone. CONCLUSION These data suggest that the SNPs in DRD2 and AKT1 may influence the treatment response to risperidone in schizophrenia patients.

Diagnostic classification of schizophrenia by neural network analysis of blood-based gene expression signatures

Gene expression profiling with microarray technology suggests that peripheral blood cells might be a surrogate for postmortem brain tissue in studies of schizophrenia. The development of an accessible peripheral biomarker would substantially help in the diagnosis of this disease. We used a bioinformatics approach to examine whether the gene expression signature in whole blood contains enough information to make a specific diagnosis of schizophrenia. Unpaired t-tests of gene expression datasets from 52 antipsychotics-free schizophrenia patients and 49 normal controls identified 792 differentially expressed probes. Functional profiling with DAVID revealed that eleven of these genes were previously reported to be associated with schizophrenia, and 73 of them were expressed in the brain tissue. We analyzed the datasets with one of the supervised classifiers, artificial neural networks (ANNs). The samples were subdivided into training and testing sets. Quality filtering and stepwise forward selection identified 14 probes as predictors of the diagnosis. ANNs were then trained with the selected probes as the input and the training set for known diagnosis as the output. The constructed model achieved 91.2% diagnostic accuracy in the training set and 87.9% accuracy in the hold-out testing set. On the other hand, hierarchical clustering, a standard but unsupervised classifier, failed to separate patients and controls. These results suggest analysis of a blood-based gene expression signature with the supervised classifier, ANNs, might be a diagnostic tool for schizophrenia.

Association analysis of nuclear receptor Rev-erb alpha gene (NR1D1) with mood disorders in the Japanese population

Several investigations have suggested that alterations in circadian rhythms may lay the foundation for the development of mood disorder (bipolar disorder and major depressive disorder). Recently, the nuclear receptor Rev-erb alpha was reported to be related to circadian rhythms, and was shown to be involved in the biological action of lithium in vitro. These evidences indicate that the nuclear receptor Rev-erb alpha gene (NR1D1) is a good candidate gene for the pathogenesis of mood disorders. To evaluate the association between NR1D1 and mood disorders, we conducted a case-control study of Japanese samples (147 bipolar patients, 322 major depressive disorder patients and 360 controls) with three tagging SNPs selected by HapMap database. One SNP showed an association with bipolar disorder in females. After Bonferroni correction for multiple testing, however, this significance disappeared. No significant association was found with major depressive disorder. In conclusion, our findings suggest that NR1D1 does not play a major role in the pathophysiology of mood disorders in the Japanese population.

SIRT1 gene is associated with major depressive disorder in the Japanese population.

BACKGROUND Many studies including our previous ones as to PROKR2 and CLOCK have suggested that circadian genes may be involved in the mechanisms of mood disorders and their treatment responses. Also several recent investigations have reported that SIRT1 plays an important role in the circadian system as conventional circadian clock genes, and also have some relation to dopaminergic metabolism. So we considered the SIRT1 gene to be a good candidate gene for the pathophysiology for MDD and SSRI responses in MDD, and conducted a case-control study using four tagging SNPs (450 MDD patients, including 261 patients treated by SSRIs and 766 controls). METHOD The MDD patients in this study had scores of 12 or higher on the 17 items of the Structured Interview Guide for Hamilton Rating Scale for Depression (SIGH-D). We defined a clinical response as a decrease of more than 50% in baseline SIGH-D within 8 weeks, and clinical remission as an SIGH-D score of less than 7 at 8 weeks. Marker-trait association analysis was used to evaluate allele and genotype association with the chi-square test, and haplotype association analysis was evaluated with a likelihood ratio test. RESULT We found an association between rs10997875 in SIRT1 gene and MDD in the allele/genotype analysis. In addition, this significance of these associations survived Bonferroni correction. However, we did not find any association between SIRT1 gene and SSRI therapeutic response in MDD in the allele/genotype analysis or haplotype analysis. LIMITATIONS A replication study using larger samples may be required for conclusive results, since our sample size was small. CONCLUSIONS Our results suggest that rs10997875 in SIRT1 gene may play a role in the pathophysiology of MDD in the Japanese population.

Serotonin 1A receptor gene and major depressive disorder: an association study and meta-analysis.

Several genetic studies have shown an association between the 5-HT1A receptor gene (HTR1A) and major depressive disorder (MDD); however, results have been rather inconsistent. Moreover, to our knowledge, no association study on HTR1A and MDD in the Japanese population has been reported. Therefore, to evaluate the association between HTR1A and MDD, we conducted a case–control study of Japanese population samples with two single-nucleotide polymorphisms (SNPs), including rs6295 (C-1019G) in HTR1A. In addition, we conducted a meta-analysis of rs6295, which has been examined in other papers. Using one functional SNP (rs6295) and one tagging SNP (rs878567) selected with the HapMap database, we conducted a genetic association analysis of case–control samples (331 patients with MDD and 804 controls) in the Japanese population. Seven population-based association studies, including this study, met our criteria for the meta-analysis of rs6295. We found an association between rs878567 and Japanese MDD patients in the allele-wise analysis, but the significance of this association did not remain after Bonferronis correction. We also did not detect any association between HTR1A and MDD in the allele/genotype-wise or haplotype-wise analysis. On the other hand, we detected an association between rs6295 and MDD in the meta-analysis (P(Z)=0.0327). In an explorative analysis, rs6295 was associated with Asian MDD patients after correction for multiple testing (P(Z)=0.0176), but not with Caucasian MDD patients (P(Z)=0.138). Our results suggest that HTR1A may not have a role in the pathophysiology of Japanese MDD patients. On the other hand, according to the meta-analysis, HTR1A was associated with MDD patients, especially in the Asian population.

BDNF is not associated with schizophrenia: Data from a Japanese population study and meta-analysis

A variety of evidence suggests brain-derived neurotrophic factor (BDNF) as a candidate gene for schizophrenia, and several genetic studies have shown a significant association between the disease and certain SNPs within BDNF (specifically, Val66Met and C270T). According to a recent study, the functional microsatellite marker BDNF-LCPR (BDNF-linked complex polymorphic region), which affects the expression level of BDNF, is associated with bipolar disorder. The goals of our current study were to 1) evaluate the quality of HapMap-based linkage disequilibrium (LD) tagging of BDNF-LCPR, 2) examine whether these tagging SNPs are associated with schizophrenia in a Japanese population, and 3) conduct a meta-analysis of the two most extensively studied polymorphisms: Val66Met and C270T. We genotyped eight tagging SNPs, including Val66Met and C270T. Our LD evaluation showed that BDNF-LCPR could be represented by these tagging SNPs in controls (with 73.5% allelic coverage). However, the functional A1 allele was not captured due to its low minor allele frequency (2.2%). In a case-control study (1117 schizophrenics and 1102 controls), no association was found in single-marker or multimarker analysis. Moreover, in a meta-analysis, the Val66Met polymorphism was not associated with schizophrenia, whereas C270T showed a trend for association in a fixed model (p=0.036), but not in a random model (p=0.053). From these findings, we conclude that if BDNF is indeed associated with schizophrenia, the A1 allele in BDNF-LCPR would be the most promising candidate. Further LD evaluation, as well as an association study in which BDNF-LCPR is genotyped directly, would be required for a more conclusive result.

Positive association of the serotonin 5-HT7 receptor gene with schizophrenia in a Japanese population.

Several lines of evidence suggest that abnormalities in the serotonin system may be related to the pathophysiology of schizophrenia. The 5-HT7 receptor is considered to be a possible schizophrenia-susceptibility factor, based on findings from binding, animal, postmortem, and genomewide linkage studies. In this study, we conducted linkage disequilibrium (LD) mapping of the human 5-HT7 receptor gene (HTR7) and selected four ‘haplotype-tagging (ht) SNPs’. Using these four htSNPs, we then conducted an LD case-control association analysis in 383 Japanese schizophrenia patients and 351 controls. Two htSNPs (SNP2 and SNP5) and haplotypes were found to be associated with schizophrenia. A promoter SNP (SNP2) was further assessed in a dual-luciferase reporter assay, but it was not found to have any functional relevance. Although we failed to find an actual susceptibility variant that could modify the function of HTR7, our results support the supposition that HTR7 is a susceptibility gene for schizophrenia in this ethnic group.