Genetic insight of schizophrenia: past and future perspectives

[Neurogenetics of schizophrenia: findings from studies based on data sharing and global partnerships]

Schizophrenic psychoses are the result of a multifactorial process in which not only environmental influences but also genetic factors play an important role. These factors are based on a complex mode of inheritance that involves a large number of genetic variants. In the last three decades, biological psychiatric research has focused closely on molecular genetic aspects of the hereditary basis of schizophrenic psychoses. In particular, international consortia are combining cohorts from individual researchers, creating continuously increasing sample sizes and thus increased statistical power. As part of the Psychiatric Genomics Consortium (PGC), genome-wide association studies with tens of thousands of patients and controls have for the first time found robustly replicable markers for schizophrenic psychoses. Through intensive phenotyping, first approaches to a transdiagnostic clinical reclassification of severe mental illnesses have been established in the longitudinal PsyCourse study of the UMG Göttingen and the LMU Munich, allowing new biologically validated disease subgroups with prognostic value to be identified. For the first time environmental factors could even be examined in an African cohort that contribute to the development of the psychosis. In the coming years, the enormous technical progress in the area of genomic high-throughput technologies (next-generation sequencing) is expected to provide new knowledge not only about the influence of frequently occurring single nucleotide polymorphisms but also about rare variants. For the successful use of this technological revolution an exchange of data between research groups is essential.

Evidence for an Interaction Between NEDD4 and Childhood Trauma on Clinical Characters of Schizophrenia With Family History of Psychosis

Background: Neural precursor cell-expressed developmentally downregulated 4 (NEDD4) polymorphisms and childhood trauma (CT) are associated with schizophrenia. However, whether NEDD4 interacts with CT on symptoms of schizophrenia remains unknown. This study aimed to investigate the gene-environment interaction effect. Methods: We recruited 289 schizophrenia patients and 487 controls and genotyped rs2303579, rs3088077, rs7162435, rs11550869, and rs62043855 in their NEDD4 gene. Results: We found significant differences in the rs2303579 and rs3088077 between the two groups. Patients with the rs2303579 CC genotype had higher scores compared with other genotype (P = 0.026) in the test of positive schizophrenia syndrome scores, whereas patients with the rs3088077 TT (P = 0.037) and rs7162435 CC genotypes (P = 0.009) had higher scores compared with the other genotypes in the test of excitement factor. Patients with a family history of psychosis (FH+) reported higher negative scores (P = 0.012) than those without. Patients exposed to physical abuse (PA) reported a lower language learning and memory score (P = 0.017) and working memory score (P = 0.047) than those not. Patients exposed to sexual abuse (SA) reported a lower reasoning and problem-solving skills score (P = 0.025); those exposed to emotional neglect (EN) reported a lower social cognition score (P = 0.044); and those exposed to physical neglect reported a lower social cognition score (P = 0.036) but higher visual learning and memory score (P = 0.032). Rs3088077 could interact with EN to increase risk for schizophrenia. Optimal model rs62043855 × EA, rs3088077 × rs7162435 × rs11550869 × SA × EN and rs2303579 × rs7162435 × rs11550869 × rs62043855 × EA × PA could explain positive symptom, excitement symptom and working memory, respectively, in FH+ group. Conclusion: The study highlighted that the combined interaction of NEDD4 and CT may be associated with symptoms of schizophrenia especially for those with FH+.

ATP-binding cassette transporter 13 mRNA expression level in schizophrenia patients

The objective of this study was to investigate the expression and clinical role of ATP-binding cassette transporter 13 (ABCA13) gene previously shown to be associated with schizophrenia (SZ) through Genome-wide association studies studies. Thirty-two first-episode drug-naive SZ patients and forty-eight age and gender-matched healthy controls were enrolled in this study. We measured ABCA13 mRNA expression levels using quantitative real-time PCR at baseline and 12 weeks after antipsychotic therapy. Moreover, clinical symptoms were measured by the Positive and Negative Syndrome Scale (PANSS) at baseline and 12-week follow-up. We found that ABCA13 mRNA levels were significantly lower in SZ patients compared with healthy controls at baseline. SZ patients’ symptoms were decreased, but ABCA13 mRNA levels were increased after 12 weeks antipsychotic therapy. In addition, there was a significant difference in ABCA13 mRNA levels among SZ patients at baseline and 12-week follow-up. The ABCA13 mRNA levels were not associated with age, BMI, years of education. Of the clinical symptoms measured, the ABCA13 mRNA levels were negatively associated with the PANSS scores at baseline and 12-week follow-up. The results indicated that the ABCA13 mRNA expression level is of interest, and upon further studies, it could be used as a biomarker for SZ treatment outcome.

Exploratory study of selected nucleotide variants in GRIN1, GRIN2A and GRIN2B encoding subunits of the NMDA receptor in a targeted group of schizophrenia patients with chronic cognitive impairment

Background

Schizophrenia is a mental disease that affects approximately 1% of the population. Despite over 100 years of research, its pathomechanism has still not been clarified. Cognitive deficits, which are one of the symptomatic dimensions of schizophrenia, usually appear a few years before the first psychotic episode. Therefore, this is why they are probably the clinical manifestation of the primary pathomechanism of schizophrenia. It is also supposed that N-methyl-d-aspartate receptor (NMDA-R) insufficiency in the prefrontal cortex is responsible for cognitive deficits in schizophrenia. The study aimed to examine whether four selected single nucleotide variants in GRIN1, GRIN2A and GRIN2B encoding NMDA-R subunits, of which two have not been tested before, are linked with the selected clinical phenotype of cognitive dysfunction in schizophrenia.

Methods

The study included the targeted group of 117 patients diagnosed with schizophrenia, all with cognitive deficits and in symptomatic remission. DNA fragments including the studied polymorphisms of the NMDA receptors subunit genes were amplified by polymerase chain reaction and subjected to sequencing.

Results

The study did not confirm the presence of any of the four selected single nucleotide variants in GRIN1, GRIN2A and GRIN2B subunits of NMDA-R.

Conclusions

The finding indicates that selected single nucleotide variants in GRIN2A and GRIN2B encoding subunits of the NMDA receptor are not associated with the presence of cognitive deficits in schizophrenia.

Selected single-nucleotide variants in GRIN1, GRIN2A, and GRIN2B encoding subunits of the NMDA receptor are not biomarkers of schizophrenia resistant to clozapine: exploratory study

Background

Schizophrenia is a common mental illness whose pathogenesis is still unknown. The vulnerability and stress model in schizophrenia assume that susceptibility to the disease is mainly associated with genes. Of the five symptomatic dimensions of schizophrenia, cognitive impairment appears to be most associated with the pathogenesis of schizophrenia. The aim of the study was to explore whether selected nucleotide variants in GRIN1, GRIN2A, and GRIN2B encoding subunits of the N-methyl-d-aspartate receptor (NMDA-R) receptor occur in a selected group of patients with treatment resistant schizophrenia with cognitive impairment.

Methods

The study included 45 patients diagnosed with super refractory schizophrenia, all with cognitive deficits and chronically psychotic. DNA fragments including the studied polymorphisms of the NMDA receptors subunit genes were amplified by polymerase chain reaction and subjected to sequencing.

Results

The study did not confirm the presence of any of the four selected single-nucleotide variants in GRIN1, GRIN2A, and GRIN2B subunits of NMDA-R in the study group.

Conclusion

Results of the study indicated that the selected single-nucleotide variants are not associated both with resistance to clozapine and the presence of cognitive deficits in

schizophrenia. It is possible, however, that a more extensive sequencing along with analyzing the expression of these genes may reveal different single-nucleotide variants than those assumed in the study.

Association of circulating BDNF levels with BDNF rs6265 polymorphism in schizophrenia

Schizophrenia is a severe neuropsychiatric disorder affecting 1% of the world population. Disturbances in neuronal development and synaptic connections are important factors in the pathogenesis of schizophrenia. Brain derived neurotrophic factor (BDNF), a member of the neurotrophin family, plays a critical role in the development of neurons. Among several polymorphisms reported in BDNF, the rs6265 polymorphism is known to be associated with many neuropsychiatric diseases. This study was aimed to determine the effect of BDNF rs6265 functional polymorphism on serum BDNF concentration in patients with schizophrenia. In total, 50 schizophrenia patients and 50 controls were recruited after obtaining written informed consent. Serum BDNF levels were estimated using the ELISA method and BDNF rs6265 polymorphism was genotyped using T-ARMS PCR. Serum BDNF levels were decreased significantly in schizophrenia patients when compared to the healthy controls (p < 0.0001). Further, the rs6265 polymorphism was also not associated with the schizophrenia (p = 0.41). Intragroup analysis between different genotypes revealed no association between the serum BDNF levels and rs6265 polymorphism. Our results suggest that the functional polymorphism rs6265 is not associated with serum BDNF levels, which is in line with previous findings, which indicates that serum BDNF levels depend more on diagnostic effect than genetic effect. Replication studies on a larger study population are needed.

Novel genetic susceptibility loci identified by family based whole exome sequencing in Han Chinese schizophrenia patients

Schizophrenia (SCZ) is a highly heritable psychiatric disorder that affects approximately 1% of population around the world. However, early relevant studies did not reach clear conclusions of the genetic mechanisms of SCZ, suggesting that additional susceptibility loci that exert significant influence on SCZ are yet to be revealed. So, in order to identify novel susceptibility genes that account for the genetic risk of SCZ, we performed a systematic family-based study using whole exome sequencing (WES) in 65 Han Chinese families. The analysis of 51 SCZ trios with both unaffected parents identified 22 exonic and 1 splice-site de novo mutations (DNMs) on a total of 23 genes, and showed that 12 genes carried rare protein-altering compound heterozygous mutations in more than one trio. In addition, we identified 26 exonic or splice-site single nucleotide polymorphisms (SNPs) on 18 genes with nominal significance (P < 5 × 10-4) using a transmission disequilibrium test (TDT) in all the families. Moreover, TDT result confirmed a SCZ susceptibility locus on 3p21.1, encompassing the multigenetic region NEK4-ITIH1-ITIH3-ITIH4. Through several different strategies to predict the potential pathogenic genes in silico, we revealed 4 previous discovered susceptibility genes (TSNARE1, PBRM1, STAB1 and OLIG2) and 4 novel susceptibility loci (PSEN1, TLR5, MGAT5B and SSPO) in Han Chinese SCZ patients. In summary, we identified a list of putative candidate genes for SCZ using a family-based WES approach, thus improving our understanding of the pathology of SCZ and providing critical clues to future functional validation.

Understanding the genetics of neuropsychiatric disorders: the potential role of genomic regulatory blocks

Recent genome-wide association studies have identified numerous loci associated with neuropsychiatric disorders. The majority of these are in non-coding regions, and are commonly assigned to the nearest gene along the genome. However, this approach neglects the three-dimensional organisation of the genome, and the fact that the genome contains arrays of extremely conserved non-coding elements termed genomic regulatory blocks (GRBs), which can be utilized to detect genes under long-range developmental regulation. Here we review a GRB-based approach to assign loci in non-coding regions to potential target genes, and apply it to reanalyse the results of one of the largest schizophrenia GWAS (SWG PGC, 2014). We further apply this approach to GWAS data from two related neuropsychiatric disorders-autism spectrum disorder and bipolar disorder-to show that it is applicable to developmental disorders in general. We find that disease-associated SNPs are overrepresented in GRBs and that the GRB model is a powerful tool for linking these SNPs to their correct target genes under long-range regulation. Our analysis identifies novel genes not previously implicated in schizophrenia and corroborates a number of predicted targets from the original study. The results are available as an online resource in which the genomic context and the strength of enhancer-promoter associations can be browsed for each schizophrenia-associated SNP.

Neurotransmitter receptor genotypes associated with mental and behavioral disorders

AIM

Investigation of association studies within the field of mental and behavioral disorders is of value given their complex molecular etiology including epistatic interactions of multiple genes with small effects.

MATERIALS & METHODS

Utilizing biomedical text mining, associations are uncovered for all mental and behavioral conditions listed in Diagnostic and Statistical Manual of Mental Disorders Text Revision. Specifically, a computational pipeline is designed to retrieve neurotransmitter receptor variations from biomedical literature with a text mining approach, where unique polymorphisms are also mined.

RESULTS

Analyses of 1337 unique neurotransmitter receptors and 465 distinct conditions yield 1568 unique gene-disease associations.

CONCLUSION

This study takes an unconventional approach to association studies and generates a novel dataset of associations for disorders such as major depression and schizophrenia, which provides a global perspective for their genetic etiology.

Neuroprotective Actions of Dietary Choline

Choline is an essential nutrient for humans. It is a precursor of membrane phospholipids (e.g., phosphatidylcholine (PC)), the neurotransmitter acetylcholine, and via betaine, the methyl group donor S-adenosylmethionine. High choline intake during gestation and early postnatal development in rat and mouse models improves cognitive function in adulthood, prevents age-related memory decline, and protects the brain from the neuropathological changes associated with Alzheimer’s disease (AD), and neurological damage associated with epilepsy, fetal alcohol syndrome, and inherited conditions such as Down and Rett syndromes. These effects of choline are correlated with modifications in histone and DNA methylation in brain, and with alterations in the expression of genes that encode proteins important for learning and memory processing, suggesting a possible epigenomic mechanism of action. Dietary choline intake in the adult may also influence cognitive function via an effect on PC containing eicosapentaenoic and docosahexaenoic acids; polyunsaturated species of PC whose levels are reduced in brains from AD patients, and is associated with higher memory performance, and resistance to cognitive decline.

The impact of genetics on future drug discovery in schizophrenia

INTRODUCTION

Failures of investigational new drugs (INDs) for schizophrenia have left huge unmet medical needs for patients. Given the recent lackluster results, it is imperative that new drug discovery approaches (and resultant drug candidates) target pathophysiological alterations that are shared in specific, stratified patient populations that are selected based on pre-identified biological signatures. One path to implementing this paradigm is achievable by leveraging recent advances in genetic information and technologies. Genome-wide exome sequencing and meta-analysis of single nucleotide polymorphism (SNP)-based association studies have already revealed rare deleterious variants and SNPs in patient populations. Areas covered: Herein, the authors review the impact that genetics have on the future of schizophrenia drug discovery. The high polygenicity of schizophrenia strongly indicates that this disease is biologically heterogeneous so the identification of unique subgroups (by patient stratification) is becoming increasingly necessary for future investigational new drugs. Expert opinion: The authors propose a pathophysiology-based stratification of genetically-defined subgroups that share deficits in particular biological pathways. Existing tools, including lower-cost genomic sequencing and advanced gene-editing technology render this strategy ever more feasible. Genetically complex psychiatric disorders such as schizophrenia may also benefit from synergistic research with simpler monogenic disorders that share perturbations in similar biological pathways.

DNA methylation analysis of the EGR3 gene in patients of schizophrenia

DNA methylation has been implicated in the pathogenesis of schizophrenia. EGR3 is considered as a potential candidate gene for schizophrenia. We conducted in vitro DNA methylation reaction, Lucia luciferase activity assay, and pyrosequencing assay to assess the DNA methylation of the EGR3 expression underlying the pathophysiology of schizophrenia. We found that DNA methylation of the putative EGR3 regulatory regions attenuated Lucia luciferase activity. There was no difference in the DNA methylation pattern of EGR3 between in 50 schizophrenic patients and 47 controls. Our data suggest that DNA methylation regulated the expression of EGR3 might not be associated with schizophrenia.

The Gut-Brain Axis, BDNF, NMDA and CNS Disorders

Gastro-intestinal (GI) microbiota and the 'gut-brain axis' are proving to be increasingly relevant to early brain development and the emergence of psychiatric disorders. This review focuses on the influence of the GI tract on Brain-Derived Neurotrophic Factor (BDNF) and its relationship with receptors for N-methyl-D-aspartate (NMDAR), as these are believed to be involved in synaptic plasticity and cognitive function. NMDAR may be associated with the development of schizophrenia and a range of other psychopathologies including neurodegenerative disorders, depression and dementias. An analysis of the routes and mechanisms by which the GI microbiota contribute to the pathophysiology of BDNF-induced NMDAR dysfunction could yield new insights relevant to developing novel therapeutics for schizophrenia and related disorders. In the absence of GI microbes, central BDNF levels are reduced and this inhibits the maintenance of NMDAR production. A reduction of NMDAR input onto GABA inhibitory interneurons causes disinhibition of glutamatergic output which disrupts the central signal-to-noise ratio and leads to aberrant synaptic behaviour and cognitive deficits. Gut microbiota can modulate BDNF function in the CNS, via changes in neurotransmitter function by affecting modulatory mechanisms such as the kynurenine pathway, or by changes in the availability and actions of short chain fatty acids (SCFAs) in the brain. Interrupting these cycles by inducing changes in the gut microbiota using probiotics, prebiotics or antimicrobial drugs has been found promising as a preventative or therapeutic measure to counteract behavioural deficits and these may be useful to supplement the actions of drugs in the treatment of CNS disorders.

Association between neurological soft signs, temperament and character in patients with schizophrenia and non-psychotic relatives

The heritability of schizophrenia and most personality traits has been well established, but the role of personality in susceptibility to schizophrenia remains uncertain. The aim of this study was to test for an association between personality traits and Neurological Soft Signs (NSS), a well-known biological marker of schizophrenia, in non-psychotic relatives of patients with schizophrenia. For this purpose, we evaluated the NSS scale and personality measured by the Temperament and Character inventory (TCI-R) in three groups of subjects: 29 patients with schizophrenia, 24 unaffected relatives and 37 controls. The results showed that patients with schizophrenia were more asocial (higher harm avoidance and lower reward dependence), more perseverative (higher persistence), and more schizotypal (lower self-directedness and cooperativeness, higher self-transcendence). The unaffected relatives showed higher harm avoidance, lower self-directedness and cooperativeness than the healthy controls. Higher NSS scores and sub-scores were found in patients and non-psychotic relatives compared with the controls. Among all the patients, total NSS scores were positively correlated with harm avoidance but negatively correlated with novelty seeking and persistence. Total NSS were also correlated with low scores on self-directedness and cooperativeness, which are indicators of personality disorder. Our results show that susceptibility to NSS and to schizophrenia are both related to individual differences in the temperament and character features in non-psychotic relatives of patients with schizophrenia. High harm avoidance, low persistence, low self-directedness and low cooperativeness contribute to both the risk of NSS and schizophrenia. These findings highlight the value of using both assessments to study high risk populations.

Association of PDE4B Polymorphisms with Susceptibility to Schizophrenia: A Meta-Analysis of Case-Control Studies

Background

The PDE4B single nucleotide polymorphisms (SNPs) have been reported to be associated with schizophrenia risk. However, current findings are ambiguous or even conflicting. To better facilitate the understanding the genetic role played by PDE4B in susceptibility to schizophrenia, we collected currently available data and conducted this meta-analysis.

Methods

A comprehensive electronic literature searching of PubMed, Embase, Web of Science and Cochrane Library was performed. The association between PDE4B SNPs and schizophrenia was evaluated by odds ratios (ORs) and 95% confidence intervals (CIs) under allelic, dominant and recessive genetic models. The random effects model was utilized when high between-study heterogeneity (I² > 50%) existed, otherwise the fixed effects model was used.

Results

Five studies comprising 2376 schizophrenia patients and 3093 controls were finally included for meta-analysis. The rs1040716 was statistically significantly associated with schizophrenia risk in Asian and Caucasian populations under dominant model (OR = 0.87, 95% CI: 0.76–0.99, P = 0.04). The rs2180335 was significantly related with schizophrenia risk in Asian populations under allelic (OR = 0.82, 95% CI: 0.72–0.93, P = 0.003) and dominant (OR = 0.75, 95% CI: 0.64–0.88, P < 0.001) models. A significant association was also observed between rs4320761 and schizophrenia in Asian populations under allelic model (OR = 0.87, 95% CI: 0.75–1.00, P = 0.048). In addition, a strong association tendency was found between rs6588190 and schizophrenia in Asian populations under allelic model (OR = 0.87, 95% CI: 0.76–1.00, P = 0.055).

Conclusion

This meta-analysis suggests that PDE4B SNPs are genetically associated with susceptibility to schizophrenia. However, due to limited sample size, more large-scale, multi-racial association studies are needed to further clarify the genetic association between various PDE4B variants and schizophrenia.

Decoupling of N-acetyl-aspartate and glutamate within the dorsolateral prefrontal cortex in schizophrenia

Aberrant function of glutamatergic pathways is likely to underlie the pathology of schizophrenia. Evidence of oxidative stress in the disease pathology has also been reported. N-Acetylaspartate (NAA) is metabolically linked to both cascades and may be a key marker in exploring the interconnection of glutamatergic pathways and oxidative stress. Several studies have reported positive correlation between the levels of NAA and Glx (the sum of glutamate and glutamine) in several brain regions in healthy subjects, by using proton magnetic resonance spectroscopy ([(1)H]MRS). Interestingly, one research group recently reported decoupling of the relationship between NAA and Glx in the hippocampus of patients with schizophrenia. Here we report levels of NAA and Glx measured using [(1)H]MRS, relative to the level of creatine (Cr) as an internal control. The dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) in 25 patients with schizophrenia and 17 matched healthy controls were studied. In DLPFC, NAA/Cr and Glx/Cr were significantly positively correlated in healthy controls after correction for the effect of age and smoking status and after correction for multiple comparisons (r= 0.627, P= 0.017). However, in patients with schizophrenia, the positive correlation between NAA/Cr and Glx/Cr was not observed even after correcting for these two variables (r= -0.330, P= 0.124). Positive correlation between NAA/Cr and Glx/Cr was not observed in the ACC in both groups. Decoupling of NAA and Glx in the DLPFC may reflect the interconnection of glutamatergic pathways and oxidative stress in the pathology of schizophrenia, and may possibly be a biomarker of the disease.

Individual risk alleles of susceptibility to schizophrenia are associated with poor clinical and social outcomes

Many patients with schizophrenia have poor clinical and social outcomes. Some risk alleles closely related to the onset of schizophrenia have been reported to be associated with their clinical phenotypes, but the direct relationship between genetic vulnerability to schizophrenia and clinical/social outcomes of schizophrenia, as evaluated by both practical clinical scales and 'real-world' function, has not been investigated. We evaluated the clinical and social outcomes of 455 Japanese patients with schizophrenia by severity of illness according to the Clinical Global Impression-Severity Scale (CGI-S) and social outcomes by social adjustment/maladjustment at 5 years after the first visit. We examined whether 46 single nucleotide polymorphisms (SNPs) selected from a Japanese genome-wide association study of susceptibility to schizophrenia were associated with clinical and social outcomes. We also investigated the polygenic risk scores of 46 SNPs. Allele-wise association analysis detected three SNPs, including rs2623659 in the CUB and Sushi multiple domains-1 (CSMD1) gene, associated with severity of illness at end point. The severity of illness at end point was associated with treatment response, but not with the severity of illness at baseline. Three SNPs, including rs2294424 in the C6orf105 gene, were associated with social outcomes. Point estimates of odds ratios showed positive relationships between polygenic risk scores and clinical/social outcomes; however, the results were not statistically significant. Because these results are exploratory, we need to replicate them with a larger sample in a future study.

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.

Electrophysiological endophenotypes in rodent models of schizophrenia and psychosis

Schizophrenia is caused by a diverse array of risk factors and results in a similarly diverse set of symptoms. Electrophysiological endophenotypes lie between risks and symptoms and have the potential to link the two. Electrophysiological studies in rodent models, described here, demonstrate that widely differing risk factors result in a similar set of core electrophysiological endophenotypes, suggesting the possibility of a shared neurobiological substrate.

Converging evidence implicates the abnormal microRNA system in schizophrenia

BACKGROUND

Previous findings are inconsistent; yet, converging evidence suggests an association between schizophrenia (SZ) and the impairment of posttranscriptional regulation of brain development through microRNA (miRNA) systems.

METHODS

This study aims to (1) compare the overall frequency of 121 rare variants (RVs) in 59 genes associated with the miRNA system in genome-wide association studies (GWAS)-derived data including 768 SZ cases and 1348 healthy controls and validated in an independent GWAS data including 1802 SZ cases and 1447 controls; (2) profile genome-wide miRNA expression in blood collected from 15 early-onset SZ (EOS) cases and 15 healthy controls; and (3) construct a miRNA-messenger RNA (mRNA) regulatory network using our previous genome-wide mRNA expression data generated from a separate sample of 18 EOS cases and 12 healthy controls.

RESULTS

Our findings indicate that: (1) In genes associated with the control of miRNAs, there are approximately 50% more RVs in SZ cases than in controls (P ≤ 2.62E-10); (2) The observed lower miRNA activity in EOS patients compared with the healthy controls suggests that miRNAs are abnormally downregulated; (3) There exists a predicted regulatory network among some downregulated miRNAs and some upregulated mRNAs.

CONCLUSIONS

Collectively, results from all 3 lines of evidence, suggest that the genetically based dysregulation of miRNA systems undermines miRNAs' inhibitory effects, resulting in the abnormal upregulation of genome transcription in the development of SZ.

Complexin2 modulates working memory-related neural activity in patients with schizophrenia

The specific contribution of risk or candidate gene variants to the complex phenotype of schizophrenia is largely unknown. Studying the effects of such variants on brain function can provide insight into disease-associated mechanisms on a neural systems level. Previous studies found common variants in the complexin2 (CPLX2) gene to be highly associated with cognitive dysfunction in schizophrenia patients. Similarly, cognitive functioning was found to be impaired in Cplx2 gene-deficient mice if they were subjected to maternal deprivation or mild brain trauma during puberty. Here, we aimed to study seven common CPLX2 single-nucleotide polymorphisms (SNPs) and their neurogenetic risk mechanisms by investigating their relationship to a schizophrenia-related functional neuroimaging intermediate phenotype. We examined functional MRI and genotype data collected from 104 patients with DSM-IV-diagnosed schizophrenia and 122 healthy controls who participated in the Mind Clinical Imaging Consortium study of schizophrenia. Seven SNPs distributed over the whole CPLX2 gene were tested for association with working memory-elicited neural activity in a frontoparietal neural network. Three CPLX2 SNPs were significantly associated with increased neural activity in the dorsolateral prefrontal cortex and intraparietal sulcus in the schizophrenia sample, but showed no association in healthy controls. Since increased working memory-related neural activity in individuals with or at risk for schizophrenia has been interpreted as 'neural inefficiency,' these findings suggest that certain variants of CPLX2 may contribute to impaired brain function in schizophrenia, possibly combined with other deleterious genetic variants, adverse environmental events, or developmental insults.

Schizophrenia and the gut-brain axis

Several risk factors for the development of schizophrenia can be linked through a common pathway in the intestinal tract. It is now increasingly recognized that bidirectional communication exists between the brain and the gut that uses neural, hormonal, and immunological routes. An increased incidence of gastrointestinal (GI) barrier dysfunction, food antigen sensitivity, inflammation, and the metabolic syndrome is seen in schizophrenia. These findings may be influenced by the composition of the gut microbiota. A significant subgroup of patients may benefit from the initiation of a gluten and casein-free diet. Antimicrobials and probiotics have therapeutic potential for reducing the metabolic dysfunction and immune dysregulation seen in patients with schizophrenia.

Microbiota regulation of the Mammalian gut-brain axis

The realization that the microbiota-gut-brain axis plays a critical role in health and disease has emerged over the past decade. The brain-gut axis is a bidirectional communication system between the central nervous system (CNS) and the gastrointestinal tract. Regulation of the microbiota-brain-gut axis is essential for maintaining homeostasis, including that of the CNS. The routes of this communication are not fully elucidated but include neural, humoral, immune, and metabolic pathways. A number of approaches have been used to interrogate this axis including the use of germ-free animals, probiotic agents, antibiotics, or animals exposed to pathogenic bacterial infections. Together, it is clear that the gut microbiota can be a key regulator of mood, cognition, pain, and obesity. Understanding microbiota-brain interactions is an exciting area of research which may contribute new insights into individual variations in cognition, personality, mood, sleep, and eating behavior, and how they contribute to a range of neuropsychiatric diseases ranging from affective disorders to autism and schizophrenia. Finally, the concept of psychobiotics, bacterial-based interventions with mental health benefit, is also emerging.

Significant association between DRD3 gene body methylation and schizophrenia

The current study was the first one to reveal the contribution of DRD3 methylation to the risk of different (SCZ) subtypes. This study comprised a total of 30 paranoid (15 males and 15 females) and 29 undifferentiated (15 males and 14 females) SCZ patients and 26 age- and gender-matched controls. Our results showed a significant association of CpG2 with SCZ. A breakdown analysis by gender showed that CpG2 and CpG3 methylation were significantly higher in male patients than male controls, and that CpG5 methylation was significantly higher in female patients than female controls. A further breakdown analysis by both gender and SCZ subtype showed that CpG2 and CpG3 methylation were significantly higher in male paranoid SCZ and male undifferentiated SCZ than male controls. In contrast, CpG2 and CpG3 methylation were significantly lower in female undifferentiated SCZ than female controls. Additionally, CpG5 methylation was significantly higher in female paranoid SCZ than female controls. In conclusion, our findings supported that DRD3 gene body hypermethylation was significantly associated with the risk of SCZ. Future study is needed to clarify the mechanisms by which DRD3 gene body hypermethylation contributes to the risk of SCZ.

Genomics of schizophrenia: time to consider the gut microbiome?

Research into the genomics of schizophrenia promises much, but so far is resplendent with failures to replicate, and has yielded little of therapeutic potential. Within our bodies resides a dynamic population of gut microbes forming a symbiotic superorganism comprising a myriad of bacteria of approximately 10(14) cells, containing 100 times the number of genes of the human genome and weighing approximately the same as the human brain. Recent preclinical investigations indicate that these microbes majorly impact on cognitive function and fundamental behavior patterns, such as social interaction and stress management. We are pivotally dependent on the neuroactive substances produced by such bacteria. The biological diversity of this ecosystem is established in the initial months of life and is highly impacted upon by environmental factors. To date, this vast quantity of DNA has been largely ignored in schizophrenia research. Perhaps it is time to reconsider this omission.

Towards indicated prevention of psychosis: using probabilistic assessments of transition risk in psychosis prodrome

The concept of indicated prevention has proliferated in psychiatry, and accumulating evidence suggests that it may indeed be possible to prevent or delay the onset of a first episode of psychosis though adequate interventions in individuals deemed at clinical high risk (CHR) for such an event. One challenge undermining these efforts is the relatively poor predictive accuracy of clinical assessments used in practice for CHR individuals, often leading to diagnostic and therapeutic uncertainty reflected in clinical guidelines promoting a 'watch and wait' approach to CHR patients. Using data from published studies, and employing predictive models based on the odds-ratio form of Bayes' rule, we simulated scenarios where clinical interview, neurocognitive testing, structural magnetic resonance imaging and electrophysiology are part of the initial assessment process of a CHR individual (extended diagnostic approach). Our findings indicate that for most at-risk patients, at least three of these assessments are necessary to arrive at a clinically meaningful differentiation into high- intermediate-, and low-risk groups. In particular, patients with equivocal results in the initial assessments require additional diagnostic testing to produce an accurate risk profile forming part of the comprehensive initial assessment. The findings may inform future research into reliable identification and personalized therapeutic targeting of CHR patients, to prevent transition to full-blown psychosis.

Dysbindin-associated proteome in the p2 synaptosome fraction of mouse brain

The gene DTNBP1 encodes the protein dysbindin and is among the most promising and highly investigated schizophrenia-risk genes. Accumulating evidence suggests that dysbindin plays an important role in the regulation of neuroplasticity. Dysbindin was reported to be a stable component of BLOC-1 complex in the cytosol. However, little is known about the endogenous dysbindin-containing complex in the brain synaptosome. In this study, we investigated the associated proteome of dysbindin in the P2 synaptosome fraction of mouse brain. Our data suggest that dysbindin has three isoforms associating with different complexes in the P2 fraction of mouse brain. To facilitate immunopurification, BAC transgenic mice expressing a tagged dysbindin were generated, and 47 putative dysbindin-associated proteins, including all components of BLOC-1, were identified by mass spectrometry in the dysbindin-containing complex purified from P2. The interactions of several selected candidates, including WDR11, FAM91A1, snapin, muted, pallidin, and two proteasome subunits, PSMD9 and PSMA4, were verified by coimmunoprecipitation. The specific proteasomal activity is significantly reduced in the P2 fraction of the brains of the dysbindin-null mutant (sandy) mice. Our data suggest that dysbindin is functionally interrelated to the ubiquitin-proteasome system and offer a molecular repertoire for future study of dysbindin functional networks in brain.

Inflammatory molecular signature associated with infectious agents in psychosis

Schizophrenia (SZ) is a devastating mental condition with onset in young adulthood. The identification of molecular biomarkers that reflect illness pathology is crucial. Recent evidence suggested immune and inflammatory cascades in conjunction with infection may play a role in the pathology. To address this question, we investigated molecular changes in cerebrospinal fluid (CSF) from antipsychotic-naïve patients with SZ and at risk mental status for psychosis (ARMS), in comparison with healthy controls (HCs). We measured 90 analytes using a broad multiplex platform focusing on immune and inflammatory cascades then selected 35 with our quality reporting criteria for further analysis. We also examined Toxoplasma gondii (TG) and herpes simplex virus 1 antibody levels in CSF. We report that expression of 15 molecules was significantly altered in the patient groups (SZ and ARMS) compared with HCs. The majority of these molecular changes (alpha-2-macroglobulin [α2M], fibrinogen, interleukin-6 receptor [IL-6R], stem cell factor [SCF], transforming growth factor alpha [TGFα], tumor necrosis factor receptor 2 [TNFR2], IL-8, monocyte chemotactic protein 2 [MCP-2/CCL8], testosterone [for males], angiotensin converting enzyme [ACE], and epidermal growth factor receptor) were consistent between SZ and ARMS patients, suggesting these may represent trait changes associated with psychotic conditions in general. Interestingly, many of these analytes (α2M, fibrinogen, IL-6R, SCF, TGFα, TNFR2, IL-8, MCP-2/CCL8, and testosterone [for males]) were exacerbated in subjects with ARMS compared with subjects with SZ. Although further studies are needed, we optimistically propose that these molecules may be good candidates for predictive markers for psychosis from an early stage. Lastly, reduction of IL-6R, TGFα, and ACE was correlated with positivity of TG antibody in the CSF, suggesting possible involvement of TG infection in the pathology.

Meta-analyses of 10 polymorphisms associated with the risk of schizophrenia

Schizophrenia (SCZ) is a severe complex psychiatric disorder that generates problems for the associated family and society and causes disability with regards to work for patients. The aim of the present study was to assess the contribution of 10 genetic polymorphisms to SCZ susceptibility. Meta-analyses were conducted using the data without a limitation for time or language. A total of 27 studies with 7 genes and 10 polymorphisms were selected for the meta-analyses. Two polymorphisms were found to be significantly associated with SCZ. SNAP25 rs3746544 was shown to increase the SCZ risk by 18% [P=0.01; odds ratio (OR), 1.18; 95% confidence interval (CI), 1.05-1.34] and GRIK3 rs6691840 was found to increase the risk by 30% (P=0.008; OR, 1.30; 95% CI, 1.07-1.58). Significant results were found under the dominant (P=0.001; OR, 1.36; 95% CI, 1.13-1.65) and additive (P=0.02; OR, 1.45; 95% CI, 1.06-1.98) model for the SNAP25 rs3746544 polymorphism and under the additive model for the GRIK3 rs6691840 polymorphism (P=0.03; OR, 1.73; 95% CI, 1.04-2.85). There were no significant results observed for the other eight polymorphisms, which were CCKAR rs1800857, CHRNA7 rs904952, CHRNA7 rs6494223, CHRNA7 rs2337506, DBH Ins>Del, FEZ1 rs559668, FEZ1 rs597570 and GCLM rs2301022. In conclusion, the present meta-analyses indicated that the SNAP25 rs3746544 and GRIK3 rs6691840 polymorphisms were risk factors of SCZ, which may provide valuable information for the clinical diagnosis of SCZ.