Exome sequencing of Japanese schizophrenia multiplex families supports the involvement of calcium ion channels.

BACKGROUND: Most sequencing studies of schizophrenia (SCZ) have focused on de novo genetic variants due to interpretability. However, investigating shared rare variants among patients in the same multiplex family is also important. Relatively large-scale analyses of SCZ multiplex families have been done in Caucasian populations, but whether detected variants are also pathogenic in the Japanese population is unclear because of ethnic differences in rare variants. MATERIALS AND METHODS: We performed whole-exome sequencing (WES) of 14 Japanese SCZ multiplex families. After quality control and filtering, we identified rare variants shared among affected persons within the same family. A gene ontology (GO) analysis was performed to identify gene categories possibly affected by these candidate variants. RESULTS: We found 530 variants in 486 genes as potential candidate variants from the 14 SCZ multiplex families examined. The GO analysis demonstrated significant enrichment in calcium channel activity. CONCLUSION: This study provides supporting evidence that calcium ion channel activity is involved in SCZ. WES of multiplex families is a potential means of identifying disease-associated rare variants for SCZ.

Functional characterization of rare NRXN1 variants identified in autism spectrum disorders and schizophrenia.

BACKGROUND: Rare genetic variants contribute to the etiology of both autism spectrum disorder (ASD) and schizophrenia (SCZ). Most genetic studies limit their focus to likely gene-disrupting mutations because they are relatively easier to interpret their effects on the gene product. Interpretation of missense variants is also informative to some pathophysiological mechanisms of these neurodevelopmental disorders; however, their contribution has not been elucidated because of relatively small effects. Therefore, we characterized missense variants detected in NRXN1, a well-known neurodevelopmental disease-causing gene, from individuals with ASD and SCZ. METHODS: To discover rare variants with large effect size and to evaluate their role in the shared etiopathophysiology of ASD and SCZ, we sequenced NRXN1 coding exons with a sample comprising 562 Japanese ASD and SCZ patients, followed by a genetic association analysis in 4273 unrelated individuals. Impact of each missense variant detected here on cell surface expression, interaction with NLGN1, and synaptogenic activity was analyzed using an in vitro functional assay and in silico three-dimensional (3D) structural modeling. RESULTS: Through mutation screening, we regarded three ultra-rare missense variants (T737M, D772G, and R856W), all of which affected the LNS4 domain of NRXN1α isoform, as disease-associated variants. Diagnosis of individuals with T737M, D772G, and R856W was 1ASD and 1SCZ, 1ASD, and 1SCZ, respectively. We observed the following phenotypic and functional burden caused by each variant. (i) D772G and R856W carriers had more serious social disabilities than T737M carriers. (ii) In vitro assay showed reduced cell surface expression of NRXN1α by D772G and R856W mutations. In vitro functional analysis showed decreased NRXN1α-NLGN1 interaction of T737M and D772G mutants. (iii) In silico 3D structural modeling indicated that T737M and D772G mutations could destabilize the rod-shaped structure of LNS2-LNS5 domains, and D772G and R856W could disturb N-glycan conformations for the transport signal. CONCLUSIONS: The combined data suggest that missense variants in NRXN1 could be associated with phenotypes of neurodevelopmental disorders beyond the diagnosis of ASD and/or SCZ.

Aberrant functional connectivity between the thalamus and visual cortex is related to attentional impairment in schizophrenia.

Resting-state (rs) functional magnetic resonance imaging (fMRI) studies have revealed dysfunctional thalamocortical functional connectivity (FC) in schizophrenia. However, the relationship between thalamocortical FC and cognitive impairment has not been thoroughly investigated. We hypothesized that aberrant thalamocortical FC is related to attention deficits in schizophrenia. Thirty-eight patients with schizophrenia and 38 matched healthy controls underwent rs-fMRI and task fMRI while performing a Flanker task. We observed decreased left thalamic activation in patients with schizophrenia using task fMRI to determine the thalamic seed. A seed-based analysis using this seed was performed in the whole brain to assess differences in thalamocortical FC between the groups. Significantly worse performance was observed in the patient group. The rs-fMRI analysis revealed significantly increased FC between the left thalamus seed and the occipital cortices/postcentral gyri in patients when compared to controls. In the patient group, significant positive correlations were observed between the degree of FC from the left thalamus to the bilateral occipital gyri, which correspond to the visual cortex, and the Flanker effect. No significant correlation was detected in the control group. These results indicate that aberrant FC between the left thalamus and the visual cortex is related to attention deficits in schizophrenia.

An association between serotonin receptor 3B gene (HTR3B) and treatment-resistant schizophrenia (TRS) in a Japanese population.

Genetic factors are thought to be involved in the development of treatment-resistant schizophrenia (TRS). Since several antipsychotic drugs inhibit the release of neurotransmitters via the serotonin receptors 3 (5-HT3), a dysfunction of this kind of receptor might be associated with the development of TRS. Thus, single-marker and haplotype analyses of the tag-single nucleotide polymorphisms (SNPs) of the 5-HT3B subunit gene (HTR3B) were performed in TRS (n = 101) and non-TRS (n = 244) patients. The deletion allele at the 3 bp-insertion/deletion polymorphism site (-100_-102delAAG) located in the putative HTR3B promoter region is significantly more frequent in the TRS group than the insertion allele by a single-marker comparison (p = 0.031). In addition, luciferase promoter assays showed that the deletion allele exhibited significantly higher transcriptional activity than the insertion allele in COS7 cells (p < 0.05). These results suggest that HTR3B is involved in the development of TRS in the Japanese population.

Association of SOX10 with schizophrenia in the Japanese population.

BACKGROUND: Microarray studies of schizophrenic brains revealed decreases in the expression of myelin and oligodendrocyte-related genes. Of these genes, sex-determining region Y-box 10 (SOX10) is a major transcription factor modulating the expression of proteins involved in neurogenesis and myelination. The SOX10 gene is located on chromosome 22q13.1, a region repeatedly reported to show positive signals in linkage studies on schizophrenia. OBJECTIVE: This study was conducted to clarify the exact role of SOX10 in the pathophysiology of schizophrenia. METHODS: We performed an association analysis of SOX10 in a Japanese population of 915 schizophrenic patients and 927 controls. Genotyping was carried out using polymerase chain reaction restriction fragment length polymorphism. MAIN RESULTS: One single nucleotide polymorphism of the SOX10 gene (rs139,887) was selected as a haplotype tag single nucleotide polymorphism using 96 controls. A significant association was observed in the genotype and allelic frequency of this single nucleotide polymorphism between schizophrenic patients and controls (P=0.025 and P=0.009, respectively). Especially, a significant association was found in male patients, but not female patients. We also performed a mutational search of the whole coding region, branch site, and promoter region of SOX10 in 96 schizophrenic patients, but no potential functional polymorphisms were detected. CONCLUSION: This study suggests that the SOX10 gene is related to the development of schizophrenia in the Japanese population.

Association study between the transferrin gene and schizophrenia in the Japanese population.

Several lines of evidence, including diffusion tensor imaging and microarray studies, indicate that abnormalities in myelination play an important role in the pathophysiology of schizophrenia. Of myelin and oligodendrocyte-related genes, a significant decrease in the mRNA levels of transferrin in schizophrenics has been reported by both microarray and quantitative polymerase chain reaction studies. We performed an association analysis of the transferrin gene in a Japanese population of 384 schizophrenic patients and 384 controls. Six single nucleotide polymorphisms were genotyped by polymerase chain reaction-restriction fragment length polymorphism and a TaqMan assay. No significant differences in genotype, allele, or haplotype frequencies of the six single nucleotide polymorphisms were observed between schizophrenic patients and controls. The present results suggest that the transferrin gene is not related to the development of schizophrenia in the Japanese population.