The emerging spectrum of allelic variation in schizophrenia: current evidence and strategies for the identification and functional characterization of common and rare variants

Exploring functional dysconnectivity in schizophrenia: alterations in eigenvector centrality mapping and insights into related genes from transcriptional profiles

Schizophrenia is a mental health disorder characterized by functional dysconnectivity. Eigenvector centrality mapping (ECM) has been employed to investigate alterations in functional connectivity in schizophrenia, yet the results lack consistency, and the genetic mechanisms underlying these changes remain unclear. In this study, whole-brain voxel-wise ECM analyses were conducted on resting-state functional magnetic resonance imaging data. A cohort of 91 patients with schizophrenia and 91 matched healthy controls were included during the discovery stage. Additionally, in the replication stage, 153 individuals with schizophrenia and 182 healthy individuals participated. Subsequently, a comprehensive analysis was performed using an independent transcriptional database derived from six postmortem healthy adult brains to explore potential genetic factors influencing the observed functional dysconnectivity, and to investigate the roles of identified genes in neural processes and pathways. The results revealed significant and reliable alterations in the ECM across multiple brain regions in schizophrenia. Specifically, there was a significant decrease in ECM in the bilateral superior and middle temporal gyrus, and an increase in the bilateral thalamus in both the discovery and replication stages. Furthermore, transcriptional analysis revealed 420 genes whose expression patterns were related to changes in ECM, and these genes were enriched mainly in biological processes associated with synaptic signaling and transmission. Together, this study enhances our knowledge of the neural processes and pathways involved in schizophrenia, shedding light on the genetic factors that may be linked to functional dysconnectivity in this disorder.

Transcriptional signatures of the whole-brain voxel-wise resting-state functional network centrality alterations in schizophrenia

Neuroimaging studies have revealed that patients with schizophrenia exhibit disrupted resting-state functional connectivity. However, the inconsistent findings across these studies have hindered our comprehensive understanding of the functional connectivity changes associated with schizophrenia, and the molecular mechanisms associated with these alterations remain largely unclear. A quantitative meta-analysis was first conducted on 21 datasets, involving 1057 patients and 1186 healthy controls, to examine disrupted resting-state functional connectivity in schizophrenia, as measured by whole-brain voxel-wise functional network centrality (FNC). Subsequently, partial least squares regression analysis was employed to investigate the relationship between FNC changes and gene expression profiles obtained from the Allen Human Brain Atlas database. Finally, gene enrichment analysis was performed to unveil the biological significance of the altered FNC-related genes. Compared with healthy controls, patients with schizophrenia show consistently increased FNC in the right inferior parietal cortex extending to the supramarginal gyrus, angular gyrus, bilateral medial prefrontal cortex, and right dorsolateral prefrontal cortex, while decreased FNC in the bilateral insula, bilateral postcentral gyrus, and right inferior temporal gyrus. Meta-regression analysis revealed that increased FNC in the right inferior parietal cortex was positively correlated with clinical score. In addition, these observed functional connectivity changes were found to be spatially associated with the brain-wide expression of specific genes, which were enriched in diverse biological pathways and cell types. These findings highlight the aberrant functional connectivity observed in schizophrenia and its potential molecular underpinnings, providing valuable insights into the neuropathology of dysconnectivity associated with this disorder.

ABCB9 polymorphism rs61955196 is associated with schizophrenia in a Chinese Han population

BACKGROUND

Schizophrenia (SCZ) is a complex disease which can be affected by both genetic and environmental factors. Prenatal famine exposure may cause changes in DNA methylation levels of genes. Meanwhile, maternal nutrition during pregnancy is a pivotal environmental factor in the development of SCZ. DNA methylation may be an intermediate factor mediating exposure to famine during pregnancy and SCZ, and DNA methylation quantitative trait loci might serve as a promising tool for linking SCZ and prenatal famine.

AIM

To analyze the association between prenatal famine exposure and SCZ risk in Northeast Han Chinese through analysis of DNA methylation related loci.

METHODS

A total of 954 Han Chinese from Northeast China were recruited, including 443 patients with SCZ and 511 healthy controls. The participants were further divided into famine (born in 1960-1962) and non-famine (born in 1963-1965) groups to investigate the effect of prenatal famine exposure. Four single-nucleotide polymorphisms (SNPs) selected according to the relevant literature were genotyped, namely, rs11917047 in PTPRG, rs2239681 in IGF2, rs3842756 in INSIGF, and rs61955196 in ABCB9. DNA were extracted from peripheral blood samples, and the genotypes of these SNP loci were detected using the improved Multiple Ligase Detection Reaction multiple SNP typing technique. The associations of the DNA methylation related SNPs with SCZ risk and prenatal famine, and their interactions were analyzed using logistic regression analysis and generalized multifactor dimensionality reduction (GMDR) software.

RESULTS

Based on the sequencing data, genotype distributions and allele frequencies of the four selected SNPs were determined. All genotype frequencies of the four SNPs in the healthy control group were tested for deviation from Hardy-Weinberg equilibrium (P > 0.05). Logistic regression analysis showed that rs61955196 was significantly associated with SCZ risk in the log-additive model [odds ratio (OR): 1.22; 95% confidence interval (CI): 1.01-1.48; P = 0.040]. We also found that the rs61955196 allele was related with an enhanced risk of SCZ (G>C, OR: 1.22; 95%CI: 1.01-1.47; P = 0.042). However, no associations were observed between rs11917047, rs2239681, or rs3842756 and SCZ risk. Under the optimal genetic model, no significant association of famine with the four SNPs was seen. Though the gene–gene interactions between rs2239681 and rs61955196 were found in GMDR analysis, none of the gene-gene interactions and gene-famine interactions were associated with the risk of SCZ.

CONCLUSION

Our study suggested that rs61955196 in ABCB9 is associated with SCZ susceptibility in Northeast Han Chinese, providing insight into genetic effects on SCZ.

Polygenic risk for schizophrenia and schizotypal traits in non-clinical subjects

BACKGROUND

Schizotypy is a putative risk phenotype for psychosis liability, but the overlap of its genetic architecture with schizophrenia is poorly understood.

METHODS

We tested the hypothesis that dimensions of schizotypy (assessed with the SPQ-B) are associated with a polygenic risk score (PRS) for schizophrenia in a sample of 623 psychiatrically healthy, non-clinical subjects from the FOR2107 multi-centre study and a second sample of 1133 blood donors.

RESULTS

We did not find correlations of schizophrenia PRS with either overall SPQ or specific dimension scores, nor with adjusted schizotypy scores derived from the SPQ (addressing inter-scale variance). Also, PRS for affective disorders (bipolar disorder and major depression) were not significantly associated with schizotypy.

CONCLUSIONS

This important negative finding demonstrates that despite the hypothesised continuum of schizotypy and schizophrenia, schizotypy might share less genetic risk with schizophrenia than previously assumed (and possibly less compared to psychotic-like experiences).

Transcriptional profile of pyramidal neurons in chronic schizophrenia reveals lamina-specific dysfunction of neuronal immunity

While the pathophysiology of schizophrenia has been extensively investigated using homogenized postmortem brain samples, few studies have examined changes in brain samples with techniques that may attribute perturbations to specific cell types. To fill this gap, we performed microarray assays on mRNA isolated from anterior cingulate cortex (ACC) superficial and deep pyramidal neurons from 12 schizophrenia and 12 control subjects using laser-capture microdissection. Among all the annotated genes, we identified 134 significantly increased and 130 decreased genes in superficial pyramidal neurons, while 93 significantly increased and 101 decreased genes were found in deep pyramidal neurons, in schizophrenia compared to control subjects. In these differentially expressed genes, we detected lamina-specific changes of 55 and 31 genes in superficial and deep neurons in schizophrenia, respectively. Gene set enrichment analysis (GSEA) was applied to the entire pre-ranked differential expression gene lists to gain a complete pathway analysis throughout all annotated genes. Our analysis revealed overrepresented groups of gene sets in schizophrenia, particularly in immunity and synapse-related pathways, suggesting the disruption of these pathways plays an important role in schizophrenia. We also detected other pathways previously demonstrated in schizophrenia pathophysiology, including cytokine and chemotaxis, postsynaptic signaling, and glutamatergic synapses. In addition, we observed several novel pathways, including ubiquitin-independent protein catabolic process. Considering the effects of antipsychotic treatment on gene expression, we applied a novel bioinformatics approach to compare our differential expression gene profiles with 51 antipsychotic treatment datasets, demonstrating that our results were not influenced by antipsychotic treatment. Taken together, we found pyramidal neuron-specific changes in neuronal immunity, synaptic dysfunction, and olfactory dysregulation in schizophrenia, providing new insights for the cell-subtype specific pathophysiology of chronic schizophrenia.

Multiple Rare Risk Coding Variants in Postsynaptic Density-Related Genes Associated With Schizophrenia Susceptibility

Objective

Schizophrenia is a chronic debilitating neurobiological disorder of aberrant synaptic connectivity and synaptogenesis. Postsynaptic density (PSD)–related proteins in N-methyl-D-aspartate receptor–postsynaptic signaling complexes are crucial to regulating the synaptic transmission and functions of various synaptic receptors. This study examined the role of PSD-related genes in susceptibility to schizophrenia.

Methods

We resequenced 18 genes encoding the disks large-associated protein (DLGAP), HOMER, neuroligin (NLGN), neurexin, and SH3 and multiple ankyrin repeat domains (SHANK) protein families in 98 schizophrenic patients with family psychiatric history using semiconductor sequencing. We analyzed the protein function of the identified rare schizophrenia-associated mutants via immunoblotting and immunocytochemistry.

Results

We identified 50 missense heterozygous mutations in 98 schizophrenic patients with family psychiatric history, and in silico analysis revealed some as damaging or pathological to the protein function. Ten missense mutations were absent from the dbSNP database, the gnomAD (non-neuro) dataset, and 1,517 healthy controls from Taiwan BioBank. Immunoblotting revealed eight missense mutants with altered protein expressions in cultured cells compared with the wild type.

Conclusion

Our findings suggest that PSD-related genes, especially the NLGN, SHANK, and DLGAP families, harbor rare functional mutations that might alter protein expression in some patients with schizophrenia, supporting contributing rare coding variants into the genetic architecture of schizophrenia.

Genes associated with gray matter volume alterations in schizophrenia

Although both schizophrenia and gray matter volume (GMV) show high heritability, however, genes accounting for GMV alterations in schizophrenia remain largely unknown. Based on risk genes identified in schizophrenia by the genome-wide association study of the Schizophrenia Working Group of the Psychiatric Genomics Consortium, we used transcription-neuroimaging association analysis to test that which of these genes are associated with GMV changes in schizophrenia. For each brain tissue sample, the expression profiles of 196 schizophrenia risk genes were extracted from six donated normal brains of the Allen Human Brain Atlas, and GMV differences between patients with schizophrenia and healthy controls were calculated based on five independent case-control structural MRI datasets (276 patients and 284 controls). Genes associated with GMV changes in schizophrenia were identified by performing cross-sample spatial correlations between expression levels of each gene and case-control GMV difference derived from the five MRI datasets integrated by harmonization and meta-analysis. We found that expression levels of 98 genes consistently showed significant cross-sample spatial correlations with GMV changes in schizophrenia. These genes were functionally enriched for chemical synaptic transmission, central nervous system development, and cell projection. Overall, this study provides a set of genes possibly associated with GMV changes in schizophrenia, which could be used as candidate genes to explore biological mechanisms underlying the structural impairments in schizophrenia.

Glutamate in schizophrenia: Neurodevelopmental perspectives and drug development

Research into the neurobiological processes that may lead to the onset of schizophrenia places growing emphasis on the glutamatergic system and brain development. Preclinical studies have shown that neurodevelopmental, genetic, and environmental factors contribute to glutamatergic dysfunction and schizophrenia-related phenotypes. Clinical research has suggested that altered brain glutamate levels may be present before the onset of psychosis and relate to outcome in those at clinical high risk. After psychosis onset, glutamate dysfunction may also relate to the degree of antipsychotic response and clinical outcome. These findings support ongoing efforts to develop pharmacological interventions that target the glutamate system and could suggest that glutamatergic compounds may be more effective in specific patient subgroups or illness stages. In this review, we consider the updated glutamate hypothesis of schizophrenia, from a neurodevelopmental perspective, by reviewing recent preclinical and clinical evidence, and discuss the potential implications for novel therapeutics.

Effects of GSTA1 and GPX3 Polymorphisms on the Risk of Schizophrenia in Chinese Han Population

PURPOSE

Several lines of evidence support the fact that the presence of oxidative stress plays an important role in the pathophysiological mechanisms of schizophrenia (SCZ). The glutathione peroxidases (GPXs) and glutathione S-transferases (GSTs) are the major antioxidant enzymes. Polymorphic variants of GPX and GST can affect the antioxidant activities of their encoded enzymes. This study explored the possible associations of the GSTA1 and GPX3 gene polymorphisms and schizophrenia in Chinese Han population.

METHODS

DNA from 648 healthy controls and 617 schizophrenic patients was genotyped for single-nucleotide polymorphisms (SNPs) rs3957357 in GSTA1 and rs736775 in GPX3 using a PCR-LDR genotyping assay. The χ² test compared differences in genetic distributions between the two groups in a case-control study. The generalized multifactor dimensionality reduction (GMDR) was used to explore the interaction between the GSTA1 gene and the GPX3 gene on the risk of SCZ.

RESULTS

Significant differences in allelic and genotypic frequencies of GSTA1 rs3957357 were present between SCZ and control groups (GSTA1 rs3957357 χ²=6.172, P=0.046 by genotype, χ²=5.847, P=0.016, odds ratio=1.329, 95% confidence interval=1.055-1.674 by allele). No significant differences in allelic or genotypic frequencies of GPX3 rs736775 were detected between cases and controls (GPX3 rs736775: χ²=2.058, P=0.357 by genotype, χ²=1.853, P=0.173, odds ratio=1.131, 95% confidence interval=0.953-1.342 by allele). Moreover, the GMDR model showed that the interaction between GSTA1 rs3957357 and GPX3 rs736775 was associated significantly with SCZ risk, P=0.0107.

CONCLUSION

Our results suggest that GSTA1 rs3957357 SNP has an effect on the risk of SCZ and the interaction between GSTA1 rs3957357and GPX3 rs736775 may affect the development of SCZ in Chinese Han population. However, these results should be validated by replication in different populations with large sample sizes.

Treatment resistant schizophrenia: Clinical, biological, and therapeutic perspectives

Treatment resistant schizophrenia (TRS) refers to the significant proportion of schizophrenia patients who continue to have symptoms and poor outcomes despite treatment. While many definitions of TRS include failure of two different antipsychotics as a minimum criterion, the wide variability in inclusion criteria has challenged the consistency and reproducibility of results from studies of TRS. We begin by reviewing the clinical, neuroimaging, and neurobiological characteristics of TRS. We further review the current treatment strategies available, addressing clozapine, the first-line pharmacological agent for TRS, as well as pharmacological and non-pharmacological augmentation of clozapine including medication combinations, electroconvulsive therapy, repetitive transcranial magnetic stimulation, deep brain stimulation, and psychotherapies. We conclude by highlighting the most recent consensus for defining TRS proposed by the Treatment Response and Resistance in Psychosis Working Group, and provide our overview of future perspectives and directions that could help advance the field of TRS research, including the concept of TRS as a potential subtype of schizophrenia.

Screening for rare epigenetic variations in autism and schizophrenia

While many studies have led to the identification of rare sequence variants linked with susceptibility to autism and schizophrenia, the contribution of rare epigenetic variations (epivariations) in these disorders remains largely unexplored. Previously we presented evidence that epivariations occur relatively frequently in the human genome, and likely contribute to a subset of congenital and neurodevelopmental disorders through the disruption of dosage-sensitive genes. Here we extend this approach, studying methylation profiles from 297 samples with autism and 767 cases with schizophrenia, identifying 84 and 268 rare epivariations in these two cohorts, respectively, that were absent from 4,860 population controls. We observed multiple features associated with these epivariations that support their pathogenic relevance, including (a) a significant enrichment for epivariations in schizophrenic individuals at genes previously linked with schizophrenia, (b) increased brain expression of genes associated with epivariations found in autism cases compared with controls, (c) in autism families, a significant excess of epivariations found specifically in affected versus unaffected sibs, (d) Gene Ontology terms linked with epivariations found in autism, including "D1 dopamine receptor binding." Our study provides additional evidence that rare epivariations likely contribute to the mutational spectra underlying neurodevelopmental disorders.

Genetic risk for schizophrenia and developmental delay is associated with shape and microstructure of midline white-matter structures

Genomic copy number variants (CNVs) are amongst the most highly penetrant genetic risk factors for neuropsychiatric disorders. The scarcity of carriers of individual CNVs and their phenotypical heterogeneity limits investigations of the associated neural mechanisms and endophenotypes. We applied a novel design based on CNV penetrance for schizophrenia (Sz) and developmental delay (DD) that allows us to identify structural sequelae that are most relevant to neuropsychiatric disorders. Our focus on brain structural abnormalities was based on the hypothesis that convergent mechanisms contributing to neurodevelopmental disorders would likely manifest in the macro- and microstructure of white matter and cortical and subcortical grey matter. Twenty one adult participants carrying neuropsychiatric risk CNVs (including those located at 22q11.2, 15q11.2, 1q21.1, 16p11.2 and 17q12) and 15 age- and gender-matched controls underwent T1-weighted structural, diffusion and relaxometry MRI. The macro- and microstructural properties of the cingulum bundles were associated with penetrance for both developmental delay and schizophrenia, in particular curvature along the anterior-posterior axis (Sz: pcorr = 0.026; DD: pcorr = 0.035) and intracellular volume fraction (Sz: pcorr = 0.019; DD: pcorr = 0.064). Further principal component analysis showed alterations in the interrelationships between the volumes of several midline white-matter structures (Sz: pcorr = 0.055; DD: pcorr = 0.027). In particular, the ratio of volumes in the splenium and body of the corpus callosum was significantly associated with both penetrance scores (Sz: p = 0.037; DD; p = 0.006). Our results are consistent with the notion that a significant alteration in developmental trajectories of midline white-matter structures constitutes a common neurodevelopmental aberration contributing to risk for schizophrenia and intellectual disability.

Assessment of a glyoxalase I frameshift variant, p.P122fs, in Japanese patients with schizophrenia

Enhanced carbonyl stress has been observed in a subgroup of patients with schizophrenia. Glyoxalase I, which is encoded by GLO1, is an enzyme that protects against carbonyl stress. In this study, we focused on the association between rare genetic variants of GLO1 and schizophrenia. First, we identified one heterozygous frameshift variant, p.P122fs, in 370 Japanese schizophrenia cases with allele frequencies of up to 1% by exon-targeted mutation screening of GLO1. We then performed an association analysis on 1282 cases and 1764 controls with this variant. The variant was found in three cases and eight controls. There was no statistically significant association between p.P122fs in GLO1 and schizophrenia (P=0.25). This frameshift variant in GLO1 might occur at near-polymorphic frequencies in the Japanese population, although further investigations using larger samples and biological analyses are needed to exclude the possibility of a low-penetrance genetic risk associated with this variant.

Association between schizophrenia polygenic risk and neural correlates of emotion perception

The neural correlates of emotion perception have been shown to be significantly altered in schizophrenia (SCZ) patients as well as their healthy relatives, possibly reflecting genetic susceptibility to the disease. The aim of the study was to investigate the association between SCZ polygenic risk and brain activity whilst testing perception of multisensory, dynamic emotional stimuli. We created SCZ polygenic risk scores (PRS) for a sample of twenty-eight healthy individuals. The PRS was based on data from the Psychiatric Genomics Consortium and was used as a regressor score in the neuroimaging analysis. The results of a multivariate brain-behaviour analysis show that higher SCZ PRS are related to increased activity in brain regions critical for emotion during the perception of threatening (angry) emotions. These results suggest that individuals with higher SCZ PRS over-activate the neural correlates underlying emotion during perception of threat, perhaps due to an increased experience of fear or neural inefficiency in emotion-regulation areas. Moreover, over-recruitment of emotion regulation regions might function as a compensation to maintain normal emotion regulation during threat perception. If replicated in larger studies, these findings may have important implications for understanding the neurophysiological biomarkers relevant in SCZ.

Functional analysis of schizophrenia genes using GeneAnalytics program and integrated databases

Schizophrenia (SCZ) is a chronic debilitating neuropsychiatric disorder with multiple risk factors involving numerous complex genetic influences. We examined and updated a master list of clinically relevant and susceptibility genes associated with SCZ reported in the literature and genomic databases dedicated to gene discovery for characterization of SCZ genes. We used the commercially available GeneAnalytics computer-based gene analysis program and integrated genomic databases to create a molecular profile of the updated list of 608 SCZ genes to model their impact in select categories (tissues and cells, diseases, pathways, biological processes, molecular functions, phenotypes and compounds) using specialized GeneAnalytics algorithms. Genes for schizophrenia were predominantly expressed in the cerebellum, cerebral cortex, medulla oblongata, thalamus and hypothalamus. Psychiatric/behavioral disorders incorporating SCZ genes included ADHD, bipolar disorder, autism spectrum disorder and alcohol dependence as well as cancer, Alzheimer's and Parkinson's disease, sleep disturbances and inflammation. Function based analysis of major biological pathways and mechanisms associated with SCZ genes identified glutaminergic receptors (e.g., GRIA1, GRIN2, GRIK4, GRM5), serotonergic receptors (e.g., HTR2A, HTR2C), GABAergic receptors (e.g., GABRA1, GABRB2), dopaminergic receptors (e.g., DRD1, DRD2), calcium-related channels (e.g., CACNA1H, CACNA1B), solute transporters (e.g., SLC1A1, SLC6A2) and for neurodevelopment (e.g., ADCY1, MEF2C, NOTCH2, SHANK3). Biological mechanisms involving synaptic transmission, regulation of membrane potential and transmembrane ion transport were identified as leading molecular functions associated with SCZ genes. Our approach to interrogate SCZ genes and their interactions at various levels has increased our knowledge and insight into the disease process possibly opening new avenues for therapeutic intervention.

Risk alleles of genes with monoallelic expression are enriched in gain-of-function variants and depleted in loss-of-function variants for neurodevelopmental disorders

Over 3000 human genes can be expressed from a single allele in one cell, and from the other allele-or both-in neighboring cells. Little is known about the consequences of this epigenetic phenomenon, monoallelic expression (MAE). We hypothesized that MAE increases expression variability, with a potential impact on human disease. Here, we use a chromatin signature to infer MAE for genes in lymphoblastoid cell lines and human fetal brain tissue. We confirm that across clones MAE status correlates with expression level, and that in human tissue data sets, MAE genes show increased expression variability. We then compare mono- and biallelic genes at three distinct scales. In the human population, we observe that genes with polymorphisms influencing expression variance are more likely to be MAE (P<1.1 × 10-6). At the trans-species level, we find gene expression differences and directional selection between humans and chimpanzees more common among MAE genes (P<0.05). Extending to human disease, we show that MAE genes are under-represented in neurodevelopmental copy number variants (CNVs) (P<2.2 × 10-10), suggesting that pathogenic variants acting via expression level are less likely to involve MAE genes. Using neuropsychiatric single-nucleotide polymorphism (SNP) and single-nucleotide variant (SNV) data, we see that genes with pathogenic expression-altering or loss-of-function variants are less likely MAE (P<7.5 × 10-11) and genes with only missense or gain-of-function variants are more likely MAE (P<1.4 × 10-6). Together, our results suggest that MAE genes tolerate a greater range of expression level than biallelic expression (BAE) genes, and this information may be useful in prediction of pathogenicity.

GPX1 Pro198Leu polymorphism and GSTP1 Ile105Val polymorphisms are not associated with the risk of schizophrenia in the Chinese Han population

Increasing lines of evidence show that oxidative stress plays a role in the pathophysiological mechanisms of schizophrenia (SCZ). Polymorphic variants of oxidative stress-related candidate genes GPX1 and GST1 can affect the antioxidant activities of their encoded enzymes. Therefore, this study aimed to explore the association between the single nucleotide polymorphisms (SNPs) of GPX1 and GSTP1 and susceptibility to schizophrenia in the Chinese Han population. DNA from 323 healthy controls and 210 schizophrenic patients was genotyped for SNPs rs1050450 in GPX1 and rs1695 in GSTP1 using a predesigned TaqMan SNP genotyping assay. Differences in genetic distributions between cases and controls were compared using the χ-test. No significant differences in allelic or genotypic frequencies of GPX1 rs1050450 or GSTP1 rs1695 were detected between cases and controls (GPX1 rs1050450: χ=0.370, P=0.831 by genotype, χ=0.377, P=0.539, odds ratio=1.145, 95% confidence interval=0.743-1.766 by allele; GSTP1 rs1695: χ=1.537, P=0.464 by genotype, χ=1.623, P=0.203, odds ratio=0.813, 95% confidence interval=0.592-1.118 by allele). Our results suggest that GPX1 rs1050450 and GSTP1 rs1695 SNPs are unlikely to play a major role in the pathogenesis of schizophrenia in the Chinese Han population. However, these results should be validated by replication in larger and independent samples.

Rare genetic variants in CX3CR1 and their contribution to the increased risk of schizophrenia and autism spectrum disorders

CX3CR1, a G protein-coupled receptor solely expressed by microglia in the brain, has been repeatedly reported to be associated with neurodevelopmental disorders including schizophrenia (SCZ) and autism spectrum disorders (ASD) in transcriptomic and animal studies but not in genetic studies. To address the impacts of variants in CX3CR1 on neurodevelopmental disorders, we conducted coding exon-targeted resequencing of CX3CR1 in 370 Japanese SCZ and 192 ASD patients using next-generation sequencing technology, followed by a genetic association study in a sample comprising 7054 unrelated individuals (2653 SCZ, 574 ASD and 3827 controls). We then performed in silico three-dimensional (3D) structural modeling and in vivo disruption of Akt phosphorylation to determine the impact of the detected variant on CX3CR1-dependent signal transduction. We detected a statistically significant association between the variant Ala55Thr in CX3CR1 with SCZ and ASD phenotypes (odds ratio=8.3, P=0.020). A 3D structural model indicated that Ala55Thr could destabilize the conformation of the CX3CR1 helix 8 and affect its interaction with a heterotrimeric G protein. In vitro functional analysis showed that the CX3CR1-Ala55Thr mutation inhibited cell signaling induced by fractalkine, the ligand for CX3CR1. The combined data suggested that the variant Ala55Thr in CX3CR1 might result in the disruption of CX3CR1 signaling. Our results strengthen the association between microglia-specific genes and neurodevelopmental disorders.

Minor allele C of rs12807809 polymorphism in NRGN contributes to the severity of psychosis in patients with Schizophrenia in South Indian population

Schizophrenia (SCZ) as a severe and complex neuropsychiatric disorder and is characterized by positive symptoms, negative symptoms and cognitive dysfunctions. Genome-wide association studies (GWAS) have identified a strong association between the single nucleotide polymorphism (SNP) rs12807809 upstream of Neurogranin (NRGN) in a European population. This evidence prompted us to conduct an association study among 1005 schizophrenia cases and 1069 controls in a South Indian Population using TaqMan Allelic discrimination method. We observed an association of rs12807809 with SCZ in this study population. Allele frequencies and genotype frequencies of rs12807809 showed significant differences between cases and control subjects [p=0.0019; OR=0.69; 95% CI=(0.55-0.87)] and (p=0.0062). Further Genotype-Phenotype correlation revealed a moderate association of rs12807809 with flat affect (p=0.039) and Hallucinations (p=0.012). The ancestral non-risk C allele contributes to the severity of psychosis (p=0.039) in this population.

An Examination of Polygenic Score Risk Prediction in Individuals With First-Episode Psychosis

BACKGROUND

Polygenic risk scores (PRSs) have successfully summarized genome-wide effects of genetic variants in schizophrenia with significant predictive power. In a clinical sample of first-episode psychosis (FEP) patients, we estimated the ability of PRSs to discriminate case-control status and to predict the development of schizophrenia as opposed to other psychoses.

METHODS

The sample (445 case and 265 control subjects) was genotyped on the Illumina HumanCore Exome BeadChip with an additional 828 control subjects of African ancestry genotyped on the Illumina Multi-Ethnic Genotyping Array. To calculate PRSs, we used the results from the latest Psychiatric Genomics Consortium schizophrenia meta-analysis. We examined the association of PRSs with case-control status and with schizophrenia versus other psychoses in European and African ancestry FEP patients and in a second sample of 248 case subjects with chronic psychosis.

RESULTS

PRS had good discriminative ability of case-control status in FEP European ancestry individuals (9.4% of the variance explained, p < 10^-6), but lower in individuals of African ancestry (R² = 1.1%, p = .004). Furthermore, PRS distinguished European ancestry case subjects who went on to acquire a schizophrenia diagnosis from those who developed other psychotic disorders (R² = 9.2%, p = .002).

CONCLUSIONS

PRS was a powerful predictor of case-control status in a European sample of patients with FEP, even though a large proportion did not have an established diagnosis of schizophrenia at the time of assessment. PRS was significantly different between those case subjects who developed schizophrenia from those who did not, although the discriminative accuracy may not yet be sufficient for clinical utility in FEP.

KCNH2-3.1 expression impairs cognition and alters neuronal function in a model of molecular pathology associated with schizophrenia

Overexpression in humans of KCNH2-3.1, which encodes a primate-specific and brain-selective isoform of the human ether-a-go-go-related potassium channel, is associated with impaired cognition, inefficient neural processing and schizophrenia. Here, we describe a new mouse model that incorporates the KCNH2-3.1 molecular phenotype. KCNH2-3.1 transgenic mice are viable and display normal sensorimotor behaviors. However, they show alterations in neuronal structure and microcircuit function in the hippocampus and prefrontal cortex, areas affected in schizophrenia. Specifically, in slice preparations from the CA1 region of the hippocampus, KCNH2-3.1 transgenic mice have fewer mature dendrites and impaired theta burst stimulation long-term potentiation. Abnormal neuronal firing patterns characteristic of the fast deactivation kinetics of the KCNH2-3.1 isoform were also observed in prefrontal cortex. Transgenic mice showed significant deficits in a hippocampal-dependent object location task and a prefrontal cortex-dependent T-maze working memory task. Interestingly, the hippocampal-dependent alterations were not present in juvenile transgenic mice, suggesting a developmental trajectory to the phenotype. Suppressing KCNH2-3.1 expression in adult mice rescues both the behavioral and physiological phenotypes. These data provide insight into the mechanism of association of KCNH2-3.1 with variation in human cognition and neuronal physiology and may explain its role in schizophrenia.

Neuropsychiatric Features in Primary Mitochondrial Disease

Mitochondrial diseases are a clinically heterogeneous group of disorders that ultimately result from dysfunction of the mitochondrial respiratory chain. There is some evidence to suggest that mitochondrial dysfunction plays a role in neuropsychiatric illness; however, the data are inconclusive. This article summarizes the available literature published in the area of neuropsychiatric manifestations in both children and adults with primary mitochondrial disease, with a focus on autism spectrum disorder in children and mood disorders and schizophrenia in adults.

The Human MSI2 Gene is Associated with Schizophrenia in the Chinese Han Population

It has been suggested that altered neurogenesis may be involved in the etiology of schizophrenia, so genes impacting on neurogenesis could be potential candidates for schizophrenia. A member of the Musashi family, the human MSI2 gene plays a substantial role in stem-cell maintenance, asymmetric division, and differentiation during neurogenesis. Our previous genome-wide association study (GWAS) implied an association of MSI2 with schizophrenia in a Han Chinese population. To further explore this association, three single-nucleotide polymorphisms (SNPs), rs9892791, rs11657292, and rs1822381, were selected for a replication study involving 921 schizophrenia cases and 1244 controls. After rigorous Bonferroni correction, two of the SNPs (rs9892791 and rs11657292) displayed significant differences in allele and genotype distribution frequencies between the case and control groups. When our GWAS and replication samples were combined, the three MSI2 SNPs were all strongly associated with schizophrenia (rs9892791: allelic P = 1.07E-5; rs11657292: allelic P = 1.95E-12; rs1822381: allelic P = 1.44E-4). These results indicate that the human MSI2 gene might be a susceptibility gene for schizophrenia and encourage future research on the functional relationship between this gene and schizophrenia.

Investigation of Rare Single-Nucleotide PCDH15 Variants in Schizophrenia and Autism Spectrum Disorders

Both schizophrenia (SCZ) and autism spectrum disorders (ASD) are neuropsychiatric disorders with overlapping genetic etiology. Protocadherin 15 (PCDH15), which encodes a member of the cadherin super family that contributes to neural development and function, has been cited as a risk gene for neuropsychiatric disorders. Recently, rare variants of large effect have been paid attention to understand the etiopathology of these complex disorders. Thus, we evaluated the impacts of rare, single-nucleotide variants (SNVs) in PCDH15 on SCZ or ASD. First, we conducted coding exon-targeted resequencing of PCDH15 with next-generation sequencing technology in 562 Japanese patients (370 SCZ and 192 ASD) and detected 16 heterozygous SNVs. We then performed association analyses on 2,096 cases (1,714 SCZ and 382 ASD) and 1,917 controls with six novel variants of these 16 SNVs. Of these six variants, four (p.R219K, p.T281A, p.D642N, c.3010-1G>C) were ultra-rare variants (minor allele frequency < 0.0005) that may increase disease susceptibility. Finally, no statistically significant association between any of these rare, heterozygous PCDH15 point variants and SCZ or ASD was found. Our results suggest that a larger sample size of resequencing subjects is necessary to detect associations between rare PCDH15 variants and neuropsychiatric disorders.

An integrated analysis tool for analyzing hybridization intensities and genotypes using new-generation population-optimized human arrays

BACKGROUND

Affymetrix Axiom single nucleotide polymorphism (SNP) arrays provide a cost-effective, high-density, and high-throughput genotyping solution for population-optimized analyses. However, no public software is available for the integrated genomic analysis of hybridization intensities and genotypes for this new-generation population-optimized genotyping platform.

RESULTS

A set of statistical methods was developed for an integrated analysis of allele frequency (AF), allelic imbalance (AI), loss of heterozygosity (LOH), long contiguous stretch of homozygosity (LCSH), and copy number variation or alteration (CNV/CNA) on the basis of SNP probe hybridization intensities and genotypes. This study analyzed 3,236 samples that were genotyped using different SNP platforms. The proposed AF adjustment method considerably increased the accuracy of AF estimation. The proposed quick circular binary segmentation algorithm for segmenting copy number reduced the computation time of the original segmentation method by 30-67 %. The proposed CNV/CNA detection, which integrates AI and LOH/LCSH detection, had a promising true positive rate and well-controlled false positive rate in simulation studies. Moreover, our real-time quantitative polymerase chain reaction experiments successfully validated the CNVs/CNAs that were identified in the Axiom data analyses using the proposed methods; some of the validated CNVs/CNAs were not detected in the Affymetrix Array 6.0 data analysis using the Affymetrix Genotyping Console. All the analysis functions are packaged into the ALICE (AF/LOH/LCSH/AI/CNV/CNA Enterprise) software.

CONCLUSIONS

ALICE and the used genomic reference databases, which can be downloaded from http://hcyang.stat.sinica.edu.tw/software/ALICE.html , are useful resources for analyzing genomic data from the Axiom and other SNP arrays.

Genetic Evaluation of Schizophrenia Using the Illumina HumanExome Chip

INTRODUCTION

Schizophrenia is a genetically heterogeneous disorder that is associated with several common and rare genetic variants. As technology involved, cost advantages of chip based genotyping was combined with information about rare variants, resulting in the Infinium HumanExome Beadchip. Using this chip, a sample of 493 patients with schizophrenia or schizoaffective disorder and 484 healthy controls was genotyped.

RESULTS

From the initial 242901 SNVs, 88306 had at least one minor allele and passed quality control. No variant reached genomewide-significant results (p<10(-8)). The SNP with the lowest p-value was rs1230345 in WISP3 (p = 3.05*10(-6)), followed by rs9311525 in CACNA2D3 (p = 1.03*10(-5)) and rs1558557 (p = 3.85*10(-05)) on chromosome 7. At the gene level, 3 genes were of interest: WISP3, on chromosome 6q21, a signally protein from the extracellular matrix. A second candidate gene is CACNA2D3, a regulator of the intracerebral calcium pathway. A third gene is TNFSF10, associated with p53 mediated apoptosis.

Increased rare duplication burden genomewide in patients with treatment-resistant schizophrenia

BACKGROUND

A significant number of patients with schizophrenia fail to respond to antipsychotic medication. Although several studies have investigated associated patient characteristics, the emerging findings from genetic studies offer further scope for study.

METHOD

In 612 schizophrenia patients with detailed clinical information, common genetic variants indexed by polygenic risk scores, and rare variants indexed by deletion and duplication burden genomewide, we explored potential genetic predictors alongside other established risk factors for treatment resistance. Clinical outcomes of treatment resistance were also calculated using lifetime measures of positive, negative/disorganized and mood symptoms as well as number of hospitalizations and suicide attempts.

RESULTS

Logistic regression models identified a significant relationship between treatment resistance and total duplication burden genomewide, years of formal schooling and age at onset. Clinically, treatment-resistant patients were characterized by greater negative/disorganized and positive symptoms and greater number of hospitalizations.

CONCLUSIONS

Taken together, these findings suggest genetic information, specifically the genomewide burden of rare copy number variants, may increase our understanding and clinical management of patients with treatment-resistant schizophrenia.

Evidence for Association of Cell Adhesion Molecules Pathway and NLGN1 Polymorphisms with Schizophrenia in Chinese Han Population

Multiple risk variants of schizophrenia have been identified by Genome-wide association studies (GWAS). As a complement for GWAS, previous pathway-based analysis has indicated that cell adhesion molecules (CAMs) pathway might be involved in the pathogenesis of schizophrenia. However, less replication studies have been reported. Our objective was to investigate the association between CAMs pathway and schizophrenia in the Chinese Han population. We first performed a pathway analysis utilizing our previous GWAS data. The CAMs pathway (hsa04514) was significantly associated with schizophrenia using hybrid gene set-based test (P = 1.03×10⁻¹⁰) and hypergeometric test (P = 5.04×10⁻⁶). Moreover, 12 genes (HLA-A, HLA-C, HLA-DOB, HLA-DPB1, HLA-DQA2, HLA-DRB1, MPZ, CD276, NLGN1, NRCAM, CLDN1 and ICAM3) were modestly significantly associated with schizophrenia (P<0.01). Then, we selected one promising gene neuroligin 1 (NLGN1) to further investigate the association between eight significant SNPs and schizophrenia in an independent sample (1814 schizophrenia cases and 1487 healthy controls). Our study showed that seven SNPs of NLGN1 and two haplotype blocks were significantly associated with schizophrenia. This association was confirmed by the results of combined analysis. Among them, SNP rs9835385 had the most significant association with schizophrenia (P = 2.83×10⁻⁷). Furthermore, in silico analysis we demonstrated that NLGN1 is preferentially expressed in human brain and SNP rs1488547 was related to the expression level. We validated the association of CAMs pathway with schizophrenia in pathway-level and identified one susceptibility gene NLGN1. Further investigation of the roles of CAMs pathway in the pathogenesis of schizophrenia is warranted.

Cognitive endophenotypes, gene-environment interactions and experience-dependent plasticity in animal models of schizophrenia

Schizophrenia is a devastating brain disorder caused by a complex and heterogeneous combination of genetic and environmental factors. In order to develop effective new strategies to prevent and treat schizophrenia, valid animal models are required which accurately model the disorder, and ideally provide construct, face and predictive validity. The cognitive deficits in schizophrenia represent some of the most debilitating symptoms and are also currently the most poorly treated. Therefore it is crucial that animal models are able to capture the cognitive dysfunction that characterizes schizophrenia, as well as the negative and psychotic symptoms. The genomes of mice have, prior to the recent gene-editing revolution, proven the most easily manipulable of mammalian laboratory species, and hence most genetic targeting has been performed using mouse models. Importantly, when key environmental factors of relevance to schizophrenia are experimentally manipulated, dramatic changes in the phenotypes of these animal models are often observed. We will review recent studies in rodent models which provide insight into gene-environment interactions in schizophrenia. We will focus specifically on environmental factors which modulate levels of experience-dependent plasticity, including environmental enrichment, cognitive stimulation, physical activity and stress. The insights provided by this research will not only help refine the establishment of optimally valid animal models which facilitate development of novel therapeutics, but will also provide insight into the pathogenesis of schizophrenia, thus identifying molecular and cellular targets for future preclinical and clinical investigations.

Common genetic risk variants are associated with positive symptoms and decision-making ability in patients with schizophrenia

Schizophrenia is a clinically heterogeneous disorder associated with broad deficits across cognitive domains. As large genomewide association studies uncover the genetic architecture of schizophrenia, the relationship between common genetic variants and clinical and cognitive characteristics will form part of an integrative approach to understanding genetic effects on the clinical phenotype. In the current study, association between common genetic risk variants and clinical and cognitive variables was investigated. Common risk variants were associated with positive symptoms and decision-making ability from the Cambridge Gambling Task with trends in other domains.

Gsx1 expression defines neurons required for prepulse inhibition

In schizophrenia, cognitive overload is thought to reflect an inability to suppress non-salient information, a process which is studied using prepulse inhibition (PPI) of the startle response. PPI is reduced in schizophrenia and routinely tested in animal models and preclinical trials of antipsychotic drugs. However, the underlying neuronal circuitry is not well understood. We used a novel genetic screen in larval zebrafish to reveal the molecular identity of neurons that are required for PPI in fish and mice. Ablation or optogenetic silencing of neurons with developmental expression of the transcription factor genomic screen homeobox 1 (gsx1) produced profound defects in PPI in zebrafish, and PPI was similarly impaired in Gsx1 knockout mice. Gsx1-expressing neurons reside in the dorsal brainstem and form synapses closely apposed to neurons that initiate the startle response. Surprisingly, brainstem Gsx1 neurons are primarily glutamatergic despite their role in a functionally inhibitory pathway. As Gsx1 has an important role in regulating interneuron development in the forebrain, these findings reveal a molecular link between control of interneuron specification and circuits that gate sensory information across brain regions.

Clinical and parental age characteristics of rare copy number variant burden in patients with schizophrenia

Copy number variant (CNV) burden, especially for rare deletions, has been associated with risk for schizophrenia as well as phenotypic differences within cognitive and neuroimaging domains. The current study investigated clinical and parental age characteristics of rare CNV burden in patients with schizophrenia. Clinical data was collected for 629 patients with schizophrenia who formed part of a genomewide association study, which included CNV data. Parental age was available for 368 patients. Correlations were calculated between burden scores and positive, negative, and mood symptoms from the Lifetime Diagnostic Psychosis Scale as well as age at onset. Patients were grouped according to number of rare deletions, duplications, or total CNVs and MANOVAs used to investigate differences in clinical and parental age characteristics. Patients with the least number of CNVs had older fathers and larger parental age difference. Patients with no deletions had older mothers and those with five or more deletions had younger mothers. Total deletion, duplication, and CNV burden, as measured by number of base pairs, were not associated with clinical or parental age differences although total rare duplication burden had a negative correlation with positive symptoms that did not survive correction for multiple testing. Likewise, a positive correlation between age at onset and total CNV burden did not survive correction. Rare CNVs are associated with differences in parental age in patients with schizophrenia. No robust clinical differences were identified. However, duplication burden may have a small protective effect against positive symptoms and age at onset may be influenced by total CNV burden. No clinical differences were associated with deletion burden measures.

Investigation of the role of TCF4 rare sequence variants in schizophrenia

Transcription factor 4 (TCF4) is one of the most robust of all reported schizophrenia risk loci and is supported by several genetic and functional lines of evidence. While numerous studies have implicated common genetic variation at TCF4 in schizophrenia risk, the role of rare, small-sized variants at this locus-such as single nucleotide variants and short indels which are below the resolution of chip-based arrays requires further exploration. The aim of the present study was to investigate the association between rare TCF4 sequence variants and schizophrenia. Exon-targeted resequencing was performed in 190 German schizophrenia patients. Six rare variants at the coding exons and flanking sequences of the TCF4 gene were identified, including two missense variants and one splice site variant. These six variants were then pooled with nine additional rare variants identified in 379 European participants of the 1000 Genomes Project, and all 15 variants were genotyped in an independent German sample (n = 1,808 patients; n = 2,261 controls). These data were then analyzed using six statistical methods developed for the association analysis of rare variants. No significant association (P < 0.05) was found. However, the results from our association and power analyses suggest that further research into the possible involvement of rare TCF4 sequence variants in schizophrenia risk is warranted by the assessment of larger cohorts with higher statistical power to identify rare variant associations.

Understanding complex transcriptome dynamics in schizophrenia and other neurological diseases using RNA sequencing

How the human brain develops and adapts with its trillions of functionally integrated synapses remains one of the greatest mysteries of life. With tremendous advances in neuroscience, genetics, and molecular biology, we are beginning to appreciate the scope of this complexity and define some of the parameters of the systems that make it possible. These same tools are also leading to advances in our understanding of the pathophysiology of neurocognitive and neuropsychiatric disorders. Like the substrate for these problems, the etiology is usually complex-involving an array of genetic and environmental influences. To resolve these influences and derive better interventions, we need to reveal every aspect of this complexity and model their interactions and define the systems and their regulatory structure. This is particularly important at the tissue-specific molecular interface between the underlying genetic and environmental influence defined by the transcriptome. Recent advances in transcriptome analysis facilitated by RNA sequencing (RNA-Seq) can provide unprecedented insight into the functional genomics of neurological disorders. In this review, we outline the advantages of this approach and highlight some early application of this technology in the investigation of the neuropathology of schizophrenia. Recent progress of RNA-Seq studies in schizophrenia has shown that there is extraordinary transcriptome dynamics with significant levels of alternative splicing. These studies only scratch the surface of this complexity and therefore future studies with greater depth and samples size will be vital to fully explore transcriptional diversity and its underlying influences in schizophrenia and provide the basis for new biomarkers and improved treatments.

The current and potential impact of genetics and genomics on neuropsychopharmacology

One justification for the major scientific and financial investments in genetic and genomic studies in medicine is their therapeutic potential, both for revealing novel targets for drugs which treat the disease process, as well as allowing for more effective and safe use of existing medications. This review considers the extent to which this promise has yet been realised within psychopharmacology, how things are likely to develop in the foreseeable future, and the key issues involved. It draws primarily on examples from schizophrenia and its treatments. One observation is that there is evidence for a range of genetic influences on different aspects of psychopharmacology in terms of discovery science, but far less evidence that meets the standards required before such discoveries impact upon clinical practice. One reason is that results reveal complex genetic influences that are hard to replicate and usually of very small effect. Similarly, the slow progress being made in revealing the genes that underlie the major psychiatric syndromes hampers attempts to apply the findings to identify novel drug targets. Nevertheless, there are some intriguing positive findings of various kinds, and clear potential for genetics and genomics to play an increasing and major role in psychiatric drug discovery.

S-SCAM, a rare copy number variation gene, induces schizophrenia-related endophenotypes in transgenic mouse model

Accumulating genetic evidence suggests that schizophrenia (SZ) is associated with individually rare copy number variations (CNVs) of diverse genes, often specific to single cases. However, the causality of these rare mutations remains unknown. One of the rare CNVs found in SZ cohorts is the duplication of Synaptic Scaffolding Molecule (S-SCAM, also called MAGI-2), which encodes a postsynaptic scaffolding protein controlling synaptic AMPA receptor levels, and thus the strength of excitatory synaptic transmission. Here we report that, in a transgenic mouse model simulating the duplication conditions, elevation of S-SCAM levels in excitatory neurons of the forebrain was sufficient to induce multiple SZ-related endophenotypes. S-SCAM transgenic mice showed an increased number of lateral ventricles and a reduced number of parvalbumin-stained neurons. In addition, the mice exhibited SZ-like behavioral abnormalities, including hyperlocomotor activity, deficits in prepulse inhibition, increased anxiety, impaired social interaction, and working memory deficit. Notably, the S-SCAM transgenic mice showed a unique sex difference in showing these behavioral symptoms, which is reminiscent of human conditions. These behavioral abnormalities were accompanied by hyperglutamatergic function associated with increased synaptic AMPA receptor levels and impaired long-term potentiation. Importantly, reducing glutamate release by the group 2 metabotropic glutamate receptor agonist LY379268 ameliorated the working memory deficits in the transgenic mice, suggesting that hyperglutamatergic function underlies the cognitive functional deficits. Together, these results contribute to validate a causal relationship of the rare S-SCAM CNV and provide supporting evidence for the rare CNV hypothesis in SZ pathogenesis. Furthermore, the S-SCAM transgenic mice provide a valuable new animal model for studying SZ pathogenesis.

Altered gene expression in schizophrenia: findings from transcriptional signatures in fibroblasts and blood

BACKGROUND

Whole-genome expression studies in the peripheral tissues of patients affected by schizophrenia (SCZ) can provide new insight into the molecular basis of the disorder and innovative biomarkers that may be of great utility in clinical practice. Recent evidence suggests that skin fibroblasts could represent a non-neural peripheral model useful for investigating molecular alterations in psychiatric disorders.

METHODS

A microarray expression study was conducted comparing skin fibroblast transcriptomic profiles from 20 SCZ patients and 20 controls. All genes strongly differentially expressed were validated by real-time quantitative PCR (RT-qPCR) in fibroblasts and analyzed in a sample of peripheral blood cell (PBC) RNA from patients (n = 25) and controls (n = 22). To evaluate the specificity for SCZ, alterations in gene expression were tested in additional samples of fibroblasts and PBCs RNA from Major Depressive Disorder (MDD) (n = 16; n = 21, respectively) and Bipolar Disorder (BD) patients (n = 15; n = 20, respectively).

RESULTS

Six genes (JUN, HIST2H2BE, FOSB, FOS, EGR1, TCF4) were significantly upregulated in SCZ compared to control fibroblasts. In blood, an increase in expression levels was confirmed only for EGR1, whereas JUN was downregulated; no significant differences were observed for the other genes. EGR1 upregulation was specific for SCZ compared to MDD and BD.

CONCLUSIONS

Our study reports the upregulation of JUN, HIST2H2BE, FOSB, FOS, EGR1 and TCF4 in the fibroblasts of SCZ patients. A significant alteration in EGR1 expression is also present in SCZ PBCs compared to controls and to MDD and BD patients, suggesting that this gene could be a specific biomarker helpful in the differential diagnosis of major psychoses.

Genetic studies of schizophrenia: an update

Schizophrenia (SCZ) is a complex and heterogeneous mental disorder that affects about 1% of global population. In recent years, considerable progress has been made in genetic studies of SCZ. A number of common variants with small effects and rare variants with relatively larger effects have been identified. These variants include risk loci identified by genome-wide association studies, rare copy-number variants identified by comparative genomic analyses, and de novo mutations identified by high-throughput DNA sequencing. Collectively, they contribute to the heterogeneity of the disease. In this review, we update recent discoveries in the field of SCZ genetics, and outline the perspectives of future directions.

Recent genetic findings in schizophrenia and their therapeutic relevance

Over 100 loci are now associated with schizophrenia risk as identified by single nucleotide polymorphisms (SNPs) in genome-wide association studies. These findings mean that 'genes for schizophrenia' have unquestionably been found. However, many questions remain unanswered, including several which affect their therapeutic significance. The SNPs individually have minor effects, and even cumulatively explain only a modest fraction of the genetic predisposition. The remainder likely results from many more loci, from rare variants, and from gene-gene and gene-environment interactions. The risk SNPs are almost all non-coding, meaning that their biological significance is unclear; probably their effects are mediated via an influence on gene regulation, and emerging evidence suggests that some key molecular events occur during early brain development. The loci include novel genes of unknown function as well as genes and pathways previously implicated in the pathophysiology of schizophrenia, e.g. NMDA receptor signalling. Genes in the latter category have the clearer therapeutic potential, although even this will be a challenging process because of the many complexities concerning the genetic architecture and mediating mechanisms. This review summarises recent schizophrenia genetic findings and some key issues they raise, particularly with regard to their implications for identifying and validating novel drug targets.

Neurodevelopment, GABA system dysfunction, and schizophrenia

The origins of schizophrenia have eluded clinicians and researchers since Kraepelin and Bleuler began documenting their findings. However, large clinical research efforts in recent decades have identified numerous genetic and environmental risk factors for schizophrenia. The combined data strongly support the neurodevelopmental hypothesis of schizophrenia and underscore the importance of the common converging effects of diverse insults. In this review, we discuss the evidence that genetic and environmental risk factors that predispose to schizophrenia disrupt the development and normal functioning of the GABAergic system.

Genetic risk for schizophrenia: convergence on synaptic pathways involved in plasticity

Recent large-scale genomic studies have revealed two broad classes of risk alleles for schizophrenia: a polygenic component of risk mediated through multiple common risk variants and rarer more highly penetrant submicroscopic chromosomal deletions and duplications, known as copy number variants. The focus of this review is on the emerging findings from the latter and subsequent exome sequencing data of smaller, deleterious single nucleotide variants and indels. In these studies, schizophrenia patients were found to have enriched de novo mutations in genes belonging to the postsynaptic density at glutamatergic synapses, particularly components of the N-methyl-D-aspartate receptor signaling complex, including the PSD-95 complex, activity-regulated cytoskeleton-associated protein interactors, the fragile X mental retardation protein complex, voltage-gated calcium channels, and genes implicated in actin cytoskeletal dynamics. The convergence of these implicated genes onto a coherent biological pathway at the synapse, with a specific role in plasticity, provides a significant advance in understanding pathogenesis and points to new targets for biological investigation. We consider the implications of these studies in the context of existing genetic data and the potential need to reassess diagnostic boundaries of neuropsychiatric disorders before discussing ways forward for more directed mechanistic studies to develop stratified, novel therapeutic approaches in the future.

Cognitive and structural neuroimaging characteristics of schizophrenia patients with large, rare copy number deletions

Large (>500 Kb), rare (frequency <1%) deletions are associated with risk for schizophrenia. The aim of the study was to characterise patients with these deletions using measures of cognition, grey-matter volume and white-matter integrity. Patients with schizophrenia and large, rare deletions (SZ-del) (n=17) were assessed on a test of intelligence, the Wechsler Abbreviated Scale of Intelligence (WASI), and compared with age- and sex-matched schizophrenia patients without large, rare deletions (SZ-nodel) (n=65), and healthy controls (HCs) (n=50). Regional grey-matter differences were investigated using voxel-based morphometry (SZ-del=9; SZ-nodel=26; HC=19). White-matter integrity was assessed using fractional anisotropy (SZ-del=9; SZ-nodel=24; HC=15). Compared with schizophrenia patients without large, rare deletions, those with large, rare deletions had lower IQ; greater grey-matter volume in clusters with peaks in the left and right cerebellum, left hippocampus, and right rectal gyrus; and increased white-matter anisotropy in the body and genu of the corpus callosum. Compared with healthy controls, patients with large, rare deletions had reduced grey matter volume in the right calcarine gyrus. In sum, patients with large, rare deletions had structural profiles intermediate to those observed in healthy controls and schizophrenia patients without large, rare deletions, but had greater impairment in intelligence.

Excess of homozygosity in the major histocompatibility complex in schizophrenia

Genome-wide association studies (GWAS) in schizophrenia have focused on additive allelic effects to identify disease risk loci. In order to examine potential recessive effects, we applied a novel approach to identify regions of excess homozygosity in an ethnically homogenous cohort: 904 schizophrenia cases and 1640 controls drawn from the Ashkenazi Jewish (AJ) population. Genome-wide examination of runs of homozygosity identified an excess in cases localized to the major histocompatibility complex (MHC). To refine this signal, we used the recently developed GERMLINE algorithm to identify chromosomal segments shared identical-by-descent (IBD) and compared homozygosity at such segments in cases and controls. We found a significant excess of homozygosity in schizophrenia cases compared with controls in the MHC (P-value = 0.003). An independent replication cohort of 548 schizophrenia cases from Japan and 542 matched healthy controls demonstrated similar effects. The strongest case-control recessive effects (P = 8.81 × 10(-8)) were localized to a 53-kb region near HLA-A, in a segment encompassing three poorly annotated genes, TRIM10, TRIM15 and TRIM40. At the same time, an adjacent segment in the Class I MHC demonstrated clear additive effects on schizophrenia risk, demonstrating the complexity of association in the MHC and the ability of our IBD approach to refine localization of broad signals derived from conventional GWAS. In sum, homozygosity in the classical MHC region appears to convey significant risk for schizophrenia, consistent with the ecological literature suggesting that homozygosity at the MHC locus may be associated with vulnerability to disease.

The onset and offset of psychosis--and what happens in between--a commentary on ‘Reappraising the long-term course and outcome of psychotic disorders: the AESOP-10 Study’ by Morgan et al. (2014)

As one would expect for a heterogeneous syndrome like schizophrenia, at the individual level the course of symptoms and disability vary widely. Mindful that the definition of recovery/remission varies widely between studies, a recent systematic review and meta-analysis reported that the proportion of those with schizophrenia who recover on both symptom and functional outcome is modest (approximately 14%). A 10-year follow-up of the English multicentre AESOP incidence study provides more 'fine-grained' insights into the time course of symptom fluctuation for schizophrenia and other psychotic disorders. We highlight selected findings from the new study and speculate on the role of different outcome domains for future study (e.g., symptom, occupational/functional, cognition, physical health, patient-nominated outcomes). Because recovery is a multifaceted process, we need to develop a panel of practical and operationalizable criteria for remission and recovery.

What causes aberrant salience in schizophrenia? A role for impaired short-term habituation and the GRIA1 (GluA1) AMPA receptor subunit

The GRIA1 locus, encoding the GluA1 (also known as GluRA or GluR1) AMPA glutamate receptor subunit, shows genome-wide association to schizophrenia. As well as extending the evidence that glutamatergic abnormalities have a key role in the disorder, this finding draws attention to the behavioural phenotype of Gria1 knockout mice. These mice show deficits in short-term habituation. Importantly, under some conditions the attention being paid to a recently presented neutral stimulus can actually increase rather than decrease (sensitization). We propose that this mouse phenotype represents a cause of aberrant salience and, in turn, that aberrant salience (and the resulting positive symptoms) in schizophrenia may arise, at least in part, from a glutamatergic genetic predisposition and a deficit in short-term habituation. This proposal links an established risk gene with a psychological process central to psychosis and is supported by findings of comparable deficits in short-term habituation in mice lacking the NMDAR receptor subunit Grin2a (which also shows association to schizophrenia). As aberrant salience is primarily a dopaminergic phenomenon, the model supports the view that the dopaminergic abnormalities can be downstream of a glutamatergic aetiology. Finally, we suggest that, as illustrated here, the real value of genetically modified mice is not as 'models of schizophrenia' but as experimental tools that can link genomic discoveries with psychological processes and help elucidate the underlying neural mechanisms.

Pre-pulse inhibition and antisaccade performance indicate impaired attention modulation of cognitive inhibition in 22q11.2 deletion syndrome (22q11DS)

BACKGROUND

22q11.2 deletion syndrome (22q11DS) is associated with a number of physical anomalies and neuropsychological deficits including impairments in executive and sensorimotor function. It is estimated that 25% of children with 22q11DS will develop schizophrenia and other psychotic disorders later in life. Evidence of genetic transmission of information processing deficits in schizophrenia suggests performance in 22q11DS individuals will enhance understanding of the neurobiological and genetic substrates associated with information processing. In this report, we examine information processing in 22q11DS using measures of startle eyeblink modification and antisaccade inhibition to explore similarities with schizophrenia and associations with neurocognitive performance.

METHODS

Startle modification (passive and active tasks; 120- and 480-ms pre-pulse intervals) and antisaccade inhibition were measured in 25 individuals with genetically confirmed 22q11DS and 30 healthy control subjects.

RESULTS

Individuals with 22q11DS exhibited increased antisaccade error as well as some evidence (trend-level effect) of impaired sensorimotor gating during the active condition, suggesting a dysfunction in controlled attentional processing, rather than a pre-attentive dysfunction using this paradigm.

CONCLUSIONS

The findings from the present study show similarities with previous studies in clinical populations associated with 22q11DS such as schizophrenia that may indicate shared dysfunction of inhibition pathways in these groups.

DSM-IV "criterion A" schizophrenia symptoms across ethnically different populations: evidence for differing psychotic symptom content or structural organization?

There is significant variation in the expression of schizophrenia across ethnically different populations, and the optimal structural and diagnostic representation of schizophrenia are contested. We contrasted both lifetime frequencies of DSM-IV criterion A (the core symptom criterion of the internationally recognized DSM classification system) symptoms and types/content of delusions and hallucinations in transethnic schizophrenia populations from Australia (n = 776), India (n = 504) and Sarawak, Malaysia (n = 259), to elucidate clinical heterogeneity. Differences in both criterion A symptom composition and symptom content were apparent. Indian individuals with schizophrenia reported negative symptoms more frequently than other sites, whereas individuals from Sarawak reported disorganized symptoms more frequently. Delusions of control and thought broadcast, insertion, or withdrawal were less frequent in Sarawak than Australia. Curiously, a subgroup of 20 Indian individuals with schizophrenia reported no lifetime delusions or hallucinations. These findings potentially challenge the long-held view in psychiatry that schizophrenia is fundamentally similar across cultural groups, with differences in only the content of psychotic symptoms, but equivalence in structural form.

Reduced CHRNA7 expression in C3H mice is associated with increases in hippocampal parvalbumin and glutamate decarboxylase-67 (GAD67) as well as altered levels of GABA(A) receptor subunits

Decreased expression of CHRNA7, the gene encoding the α7(∗) subtype of nicotinic receptor, may contribute to the cognitive dysfunction observed in schizophrenia by disrupting the inhibitory/excitatory balance in the hippocampus. C3H mice with reduced Chrna7 expression have significant reductions in hippocampal α7(∗) receptor density, deficits in hippocampal auditory gating, increased hippocampal activity as well as significant decreases in hippocampal glutamate decarboxylase-65 (GAD65) and γ-aminobutyric acid-A (GABAA) receptor levels. The current study investigated whether altered Chrna7 expression is associated with changes in the levels of parvalbumin, GAD67 and/or GABAA receptor subunits in the hippocampus from male and female C3H Chrna7 wildtype, C3H Chrna7 heterozygous and C3H Chrna7 knockout (KO) mice using quantitative Western immunoblotting. Reduced Chrna7 expression was associated with significant increases in hippocampal parvalbumin and GAD67 and with complex alterations in GABAA receptor subunits. A decrease in α3 subunit protein was seen in both female C3H Chrna7 Het and KO mice while a decrease in α4 subunit protein was also detected in C3H Chrna7 KO mice with no sex difference. In contrast, an increase in δ subunit protein was observed in C3H Chrna7 Het mice while a decrease in this subunit was observed in C3H Chrna7 KO mice, with δ subunit protein levels being greater in males than in females. Finally, an increase in γ2 subunit protein was found in C3H Chrna7 KO mice with the levels of this subunit again being greater in males than in females. The increases in hippocampal parvalbumin and GAD67 observed in C3H Chrna7 mice are contrary to reports of reductions in these proteins in the postmortem hippocampus from schizophrenic individuals. We hypothesize that the disparate results may occur because of the influence of factors other than CHRNA7 that have been found to be abnormal in schizophrenia.

Cannabis abuse and age at onset in schizophrenia patients with large, rare copy number variants

BACKGROUND

Large deletions are found to a greater extent in patients with schizophrenia compared with healthy controls. This study aims to investigate clinical symptomatology and substance abuse rates in patients with large (>500kb), rare (<1% of cohort) deletions and duplications compared with schizophrenia patients in general.

METHODS

633 schizophrenia patients, including 60 with large (>500kb), rare (<1% of cohort) deletions and 74 with large, rare duplications, who formed part of a large genome-wide association study, were assessed for alcohol and cannabis abuse rates as well as a range of symptom measures using the Diagnostic Interview for Genetic Studies (DIGS), Family Interview for Genetic Studies (FIGS), and medical records.

RESULTS

Patients with large, rare deletions had significantly less cannabis abuse rates but comparable alcohol abuse rates, with an age at onset later than those without large, rare deletions. There was no significant difference in any substance abuse or clinical symptom rates between patients with and without large, rare duplications, but an interaction did exist between cannabis abuse, duplication status, and age at onset, with cannabis abuse resulting in an earlier age at onset only in those without a large, rare duplication. Similarly, patients with a large, rare duplication had a later onset age for cannabis abuse/dependence.

CONCLUSIONS

Schizophrenia patients with large, rare deletions were less likely to have comorbid cannabis abuse over their lifetime. This provides support for a threshold model of risk with those carrying a schizophrenia-associated copy number variation less reliant on environmental insults. Patients with large, rare duplications were protected against earlier onset of schizophrenia in the presence of comorbid cannabis abuse in addition to later onset of cannabis abuse itself.

The role of prefrontal catecholamines in attention and working memory

While much progress has been made in identifying the brain regions and neurochemical systems involved in the cognitive processes disrupted in mental illnesses, to date, the level of detail at which neurobiologists can describe the chain of events giving rise to cognitive functions is very rudimentary. Much of the intense interest in understanding cognitive functions is motivated by the hope that it might be possible to understand these complex functions at the level of neurons and neural circuits. Here, we review the current state of the literature regarding how modulations in catecholamine levels within the prefrontal cortex (PFC) alter the neuronal and behavioral correlates of cognitive functions, particularly attention and working memory.