Molecular genetic gene-environment studies using candidate genes in schizophrenia: a systematic review

Synergistic effects of childhood adversity and polygenic risk in first-episode psychosis: the EU-GEI study

BACKGROUND

A history of childhood adversity is associated with psychotic disorder, with an increase in risk according to the number of exposures. However, it is not known why only some exposed individuals go on to develop psychosis. One possibility is pre-existing polygenic vulnerability. Here, we investigated, in the largest sample of first-episode psychosis (FEP) cases to date, whether childhood adversity and high polygenic risk scores for schizophrenia (SZ-PRS) combine synergistically to increase the risk of psychosis, over and above the effect of each alone.

METHODS

We assigned a schizophrenia-polygenic risk score (SZ-PRS), calculated from the Psychiatric Genomics Consortium (PGC2), to all participants in a sample of 384 FEP patients and 690 controls from the case-control component of the EU-GEI study. Only participants of European ancestry were included in the study. A history of childhood adversity was collected using the Childhood Trauma Questionnaire (CTQ). Synergistic effects were estimated using the interaction contrast ratio (ICR) [odds ratio (OR)exposure and PRS - ORexposure - ORPRS + 1] with adjustment for potential confounders.

RESULTS

There was some evidence that the combined effect of childhood adversities and polygenic risk was greater than the sum of each alone, as indicated by an ICR greater than zero [i.e. ICR 1.28, 95% confidence interval (CI) -1.29 to 3.85]. Examining subtypes of childhood adversities, the strongest synergetic effect was observed for physical abuse (ICR 6.25, 95% CI -6.25 to 20.88).

CONCLUSIONS

Our findings suggest possible synergistic effects of genetic liability and childhood adversity experiences in the onset of FEP, but larger samples are needed to increase precision of estimates.

Study protocol of the Berlin Research Initiative for Diagnostics, Genetics and Environmental Factors in Schizophrenia (BRIDGE-S)

BACKGROUND

Large-scale collaborative efforts in the field of psychiatric genetics have made substantial progress in unraveling the biological architecture of schizophrenia (SCZ). Although both genetic and environmental factors are known to play a role in schizophrenia etiology our mechanistic understanding of how they shape risk, resilience and disease trajectories remains limited.

METHODS

Here, we present the study protocol of the Berlin Research Initiative for Diagnostics, Genetic and Environmental Factors of Schizophrenia (BRIDGE-S), which aims to collect a densely phenotyped genetic cohort of 1,000 schizophrenia cases and 1,000 controls. The study's main objectives are to build a resource for i) promoting genetic discoveries and ii) genotype-phenotype associations to infer specific disease subtypes, and iii) exploring gene-environment interactions using polyrisk models. All subjects provide a biological sample for genotyping and complete a core questionnaire capturing a variety of environmental exposures, demographic, psychological and health data. Approximately 50% of individuals in the sample will further undergo a comprehensive clinical and neurocognitive assessment.

DISCUSSION

With BRIDGE-S we created a valuable database to study genomic and environmental contributions to schizophrenia risk, onset, and outcomes. Results of the BRIDGE-S study could yield insights into the etiological mechanisms of schizophrenia that could ultimately inform risk prediction, and early intervention and treatment strategies.

Is 'another' psychiatry possible?

In this paper, we examine a number of approaches that propose new models for psychiatric theory and practices: in the way that they incorporate 'social' dimensions, in the way they involve 'communities' in treatment, in the ways that they engage mental health service users, and in the ways that they try to shift the power relations within the psychiatric encounter. We examine the extent to which 'alternatives' - including 'Postpsychiatry', 'Open Dialogue', the 'Power, Threat and Meaning Framework' and Service User Involvement in Research - really do depart from mainstream models in terms of theory, practice and empirical research and identify some shortcomings in each. We propose an approach which seeks more firmly to ground mental distress within the lifeworld of those who experience it, with a particular focus on the biopsychosocial niches within which we make our lives, and the impact of systematic disadvantage, structural violence and other toxic exposures within the spaces and places that constitute and constrain many everyday lives. Further, we argue that a truly alternative psychiatry requires psychiatric professionals to go beyond simply listening to the voices of service users: to overcome epistemic injustice requires professionals to recognise that those who have experience of mental health services have their own expertise in accounting for their distress and in evaluating alternative forms of treatment. Finally we suggest that, if 'another psychiatry' is possible, this requires a radical reimagination of the role and responsibilities of the medically trained psychiatrist within and outside the clinical encounter.

Perceived stress and its associated factors among people living in post-war Districts of Northern Ethiopia: A cross-sectional study

BACKGROUND

War and conflict environments result in long-term physical and psychological consequences. Sexual violence, displacement, malnutrition, death, illness, injury, torture, and disability are some of the physical effects, whereas stress, depression, aggressive behaviors, and anxiety are some of the emotional complications of war. Hence, evidence-based interventions are required particularly to monitor mental health disorders. Thus, we aimed to investigate the prevalence of perceived stress and its associated factors among people living in post-war situations, Northern Ethiopia.

METHOD

A community-based cross-sectional study design was employed among 812 samples from April 1 to May 15, 2022. The study participants were selected using a multistage sampling technique. The data was collected through face-to-face interviews using a structured and pre-tested tool. Data were cleaned and entered into Epi-Data version 4.6 and transferred to SPSS version 25 for analysis. Binary logistic regression analysis was performed to identify determinants of perceived stress. The Hosmer-Lemeshow goodness-of-fit was applied to test for model fitness and a p-value of <0.05 was considered statistically significant.

RESULT

The prevalence of perceived stress was 76.1%, 95% CI (72.9-78.8). Age above 45 years (AOR (CI) = 2.45 (1.07-5.62), poor educational level (AOR (CI) = 5.92 (2.36-14.8), large family size (AOR (CI) = 0.48 (0.31-0.74), alcohol consumption (AOR (CI) = 0.63 (0.42-0.94), smoking (AOR (CI) = 0.17 (0.06-0.56), and exposure to multiple traumatic events (AOR (CI) = 2.38 (1.23-4.62) have shown a statistically significant association with perceived stress.

CONCLUSION

This study revealed that more than three-fourths of participants living in post-war settings were found to have perceived stress. Older age, poor level of education, large family size, alcohol consumption, smoking, and the number of traumatic events were significant associates of perceived stress. Psychotherapy that can effectively address the medical, social, and psychological well-being of the community is important to reduce the burden of perceived stress.

DNA Methylation and Schizophrenia: Current Literature and Future Perspective

Schizophrenia is a neuropsychiatric disorder characterized by dissociation of thoughts, idea, identity, and emotions. It has no central pathophysiological mechanism and precise diagnostic markers. Despite its high heritability, there are also environmental factors implicated in the development of schizophrenia. Epigenetic factors are thought to mediate the effects of environmental factors in the development of the disorder. Epigenetic modifications like DNA methylation are a risk factor for schizophrenia. Targeted gene approach studies attempted to find candidate gene methylation, but the results are contradictory. Genome-wide methylation studies are insufficient in literature and the available data do not cover different populations like the African populations. The current genome-wide studies have limitations related to the sample and methods used. Studies are required to control for these limitations. Integration of DNA methylation, gene expression, and their effects are important in the understanding of the development of schizophrenia and search for biomarkers. There are currently no precise and functional biomarkers for the disorder. Several epigenetic markers have been reported to be common in functional and peripheral tissue. This makes the peripheral tissue epigenetic changes a surrogate of functional tissue, suggesting common epigenetic alteration can be used as biomarkers of schizophrenia in peripheral tissue.

Critical review of the evidence base regarding theories conceptualising the aetiology of psychosis

A critical review of literature related to the aetiology of psychosis was conducted with specific emphasis on genetics. It was found that, although many published articles were retrieved via database searches, the format of the information was disparate in presentation leading to unnecessary inconsistences. This suggests the need for insightful collaboration by authors and standardisation of published articles to prevent academic and specialism barriers remaining as a discouragement to non-specialists wishing to access this information.

Environmental Risk Factors for Schizophrenia and Bipolar Disorder and Their Relationship to Genetic Risk: Current Knowledge and Future Directions

Schizophrenia (SZ) and bipolar disorder (BD) are severe psychiatric disorders which result from complex interplay between genetic and environmental factors. It is well-established that they are highly heritable disorders, and considerable progress has been made identifying their shared and distinct genetic risk factors. However, the 15-40% of risk that is derived from environmental sources is less definitively known. Environmental factors that have been repeatedly investigated and often associated with SZ include: obstetric complications, infections, winter or spring birth, migration, urban living, childhood adversity, and cannabis use. There is evidence that childhood adversity and some types of infections are also associated with BD. Evidence for other risk factors in BD is weaker due to fewer studies and often smaller sample sizes. Relatively few environmental exposures have ever been examined for SZ or BD, and additional ones likely remain to be discovered. A complete picture of how genetic and environmental risk factors confer risk for these disorders requires an understanding of how they interact. Early gene-by-environment interaction studies for both SZ and BD often involved candidate genes and were underpowered. Larger samples with genome-wide data and polygenic risk scores now offer enhanced prospects to reveal genetic interactions with environmental exposures that contribute to risk for these disorders. Overall, although some environmental risk factors have been identified for SZ, few have been for BD, and the extent to which these account for the total risk from environmental sources remains unknown. For both disorders, interactions between genetic and environmental risk factors are also not well understood and merit further investigation. Questions remain regarding the mechanisms by which risk factors exert their effects, and the ways in which environmental factors differ by sex. Concurrent investigations of environmental and genetic risk factors in SZ and BD are needed as we work toward a more comprehensive understanding of the ways in which these disorders arise.

Examining the independent and joint effects of genomic and exposomic liabilities for schizophrenia across the psychosis spectrum

AIMS

Psychosis spectrum disorder has a complex pathoetiology characterised by interacting environmental and genetic vulnerabilities. The present study aims to investigate the role of gene-environment interaction using aggregate scores of genetic (polygenic risk score for schizophrenia (PRS-SCZ)) and environment liability for schizophrenia (exposome score for schizophrenia (ES-SCZ)) across the psychosis continuum.

METHODS

The sample consisted of 1699 patients, 1753 unaffected siblings, and 1542 healthy comparison participants. The Structured Interview for Schizotypy-Revised (SIS-R) was administered to analyse scores of total, positive, and negative schizotypy in siblings and healthy comparison participants. The PRS-SCZ was trained using the Psychiatric Genomics Consortiums results and the ES-SCZ was calculated guided by the approach validated in a previous report in the current data set. Regression models were applied to test the independent and joint effects of PRS-SCZ and ES-SCZ (adjusted for age, sex, and ancestry using 10 principal components).

RESULTS

Both genetic and environmental vulnerability were associated with case-control status. Furthermore, there was evidence for additive interaction between binary modes of PRS-SCZ and ES-SCZ (above 75% of the control distribution) increasing the odds for schizophrenia spectrum diagnosis (relative excess risk due to interaction = 6.79, [95% confidential interval (CI) 3.32, 10.26], p < 0.001). Sensitivity analyses using continuous PRS-SCZ and ES-SCZ confirmed gene-environment interaction (relative excess risk due to interaction = 1.80 [95% CI 1.01, 3.32], p = 0.004). In siblings and healthy comparison participants, PRS-SCZ and ES-SCZ were associated with all SIS-R dimensions and evidence was found for an interaction between PRS-SCZ and ES-SCZ on the total (B = 0.006 [95% CI 0.003, 0.009], p < 0.001), positive (B = 0.006 [95% CI, 0.002, 0.009], p = 0.002), and negative (B = 0.006, [95% CI 0.004, 0.009], p < 0.001) schizotypy dimensions.

CONCLUSIONS

The interplay between exposome load and schizophrenia genetic liability contributing to psychosis across the spectrum of expression provide further empirical support to the notion of aetiological continuity underlying an extended psychosis phenotype.

Schizophrenia in a genomic era: a review from the pathogenesis, genetic and environmental etiology to diagnosis and treatment insights

Schizophrenia is a common multigenic and debilitating neurological disorder characterized by chronic psychotic symptoms and psychosocial impairment. Complex interactions of genetics and environmental factors have been implicated in etiology of schizophrenia. There is no central pathophysiology mechanism, diagnostic neuropathology, or biological markers have been defined for schizophrenia. However, a number of different hypotheses including neurodevelopmental and neurochemical hypotheses have been proposed to explain the neuropathology of schizophrenia. This review provides an overview of pathogenesis, genetic and environmental etiologies to diagnosis and treatment insights in clinical management of schizophrenia in light of the recent discoveries of genetic loci associated with susceptibility to schizophrenia.

Evaluation of the relationships of the WBP1L gene with schizophrenia and the general psychopathology scale based on a case-control study

WBP1L is a target of microRNA 137 (miR-137) and has been considered a candidate gene for schizophrenia (SCZ). To investigate the relationships between WBP1L and SCZ and its related symptom scales, a total of 5,993 Chinese Han subjects, including 2,128 SCZ patients and 3,865 controls, were enrolled. In addition, an independent sample set for replication study including 1,052 SCZ patients and 2,124 controls were also recruited. Thirty-two tag single nucleotide polymorphisms (SNPs) located within gene region of WBP1L were selected for genotyping and analyzing. The expression quantitative trait loci (eQTL) effects for the targeted SNPs were investigated with gene expression data from multiple human tissues. Rs4147157 (OR = 0.84, p = 1.51 × 10^-5 ) and rs284854 (OR = 1.14, p = 7.00 × 10^-4 ) were significantly associated with SCZ disease status and these association signals were replicated in our replication sample. A significant association was identified between rs4147157 and the general (β = -.66, p = .001) and total (β = -.8, p = .0042) scores of positive and negative syndrome scale scores in SCZ patients. Both SNPs were significant eQTL for genes around WBP1L in human brain tissues including ARL3 and AS3MT. To conclude, SNPs rs4147157 and rs284854 were associated with SCZ in the Chinese Han population. Additionally, rs4147157 was significantly associated with specific symptom features of SCZ.

Gene-Environment Interactions in Major Mental Disorders in the Czech Republic

BACKGROUND

Mental disorders affect about one-third of the human population, are typically chronic and significantly decrease the quality of life. Presently, the treatment of mental illnesses is far from adequate with a substantial proportion of the patients being pharmacoresistant and suffering from relapses. One of the reasons for this complicated situation is that we do not precisely know about the causes of mental disorders, so their treatment cannot be causal. The etiology of a mental disorder is typically based on a combination of molecular (genetic) and environmental factors.

AIM

The aim of the project is to discover the gene-environment interactions (GxE) in a wide spectrum of mental disorders.

METHODS

The design of our study is innovative in the sense that we intend to study large groups of associated mental disorders as a whole instead of in isolation. This would enable us to map out the possible environmental causal factors in detail in relation to their character, magnitude and timing. The project also allows a study of genetics (including epigenetics and microbiomes) as well as the environment simultaneously. We plan on involving three study groups: the first group are patients suffering from schizophrenia or a mood disorder such as major depression, recurrent depressive disorder and bipolar affective disorder; the second group of patients have anxiety disorders; and the third group are healthy volunteers from the general population who are genetically unrelated. All of the study subjects will undergo the following assessments: a psychiatric examination, the identification of stressful life events with the aid of a questionnaire, the examination of their reaction to stress, genetic and epigenetic (microRNA) assessments and the analysis of oral and gut microbiome.

CONCLUSION

We expect that some of the genetic as well as environmental factors in the studied mental disorders are shared, while some others are specific. We also expect that the GxE (gene-environment interaction) in schizophrenic and affective disorders will be different from the GxE in anxiety disorders and that the GxE in the studied mental disorders will differ generally from the GxE in healthy volunteers. Our results can help in the prevention and individualized treatment of a range of mental disorders.

Catechol-O-methyltransferase gene expression in stress-induced and non-stress induced schizophrenia

INTRODUCTION

As schizophrenia is a complex mental disorder and the outcome of gene-gene-environmental interactions, there are different possible pathophysiological mechanisms in different schizophrenia subtypes corresponding to various risk factors. This study was aimed at examining the impact of one of the most likely interactions, that is, 'dopamine and stress', in schizophrenia pathogenesis.

METHODS

Here, we investigated the interaction between 'war-related psychological trauma' without brain trauma and catechol-O-methyltransferase gene. Using real-time PCR analysis we measured catechol-O-methyltransferase gene expression level in the blood cells of 66 male subjects in four groups, namely veteran schizophrenia patients as 'stress-exposed schizophrenia' (S-schizophrenia), their healthy brothers as 'their genetically closest relatives' (S-siblings), schizophrenia patients without any history of significant stress as 'non-stress-exposed schizophrenia' (NoS-schizophrenia), and the control group. The results were analyzed by Relative Expression Software Tool 2009 software.

RESULTS

The catechol-O-methyltransferase gene expression was not significantly different between the S-schizophrenia and NoS-schizophrenia groups. However, compared to the control group, the catechol-O-methyltransferase expression was significantly decreased in three groups of S-schizophrenia, their healthy siblings, and NoS-schizophrenia patients.

CONCLUSION

This data supports that reduced blood catechol-O-methyltransferase expression, which may be associated with higher dopamine level, is involved both in stress-induced and non-stress-induced schizophrenia.

Unravelling the genetic basis of schizophrenia and bipolar disorder with GWAS: A systematic review

OBJECTIVES

To systematically review findings of GWAS in schizophrenia (SZ) and in bipolar disorder (BD); and to interpret findings, with a focus on identifying independent replications.

METHOD

PubMed search, selection and review of all independent GWAS in SZ or BD, published since March 2011, i.e. studies using non-overlapping samples within each article, between articles, and with those of the previous review (Li et al., 2012).

RESULTS

From the 22 GWAS included in this review, the genetic associations surviving standard GWAS-significance were for genetic markers in the regions of ACSL3/KCNE4, ADCY2, AMBRA1, ANK3, BRP44, DTL, FBLN1, HHAT, INTS7, LOC392301, LOC645434/NMBR, LOC729457, LRRFIP1, LSM1, MDM1, MHC, MIR2113/POU3F2, NDST3, NKAPL, ODZ4, PGBD1, RENBP, TRANK1, TSPAN18, TWIST2, UGT1A1/HJURP, WHSC1L1/FGFR1 and ZKSCAN4. All genes implicated across both reviews are discussed in terms of their function and implication in neuropsychiatry.

CONCLUSION

Taking all GWAS to date into account, AMBRA1, ANK3, ARNTL, CDH13, EFHD1 (albeit with different alleles), MHC, PLXNA2 and UGT1A1 have been implicated in either disorder in at least two reportedly non-overlapping samples. Additionally, evidence for a SZ/BD common genetic basis is most strongly supported by the implication of ANK3, NDST3, and PLXNA2.

Examining the independent and joint effects of molecular genetic liability and environmental exposures in schizophrenia: results from the EUGEI study

Schizophrenia is a heritable complex phenotype associated with a background risk involving multiple common genetic variants of small effect and a multitude of environmental exposures. Early twin and family studies using proxy-genetic liability measures suggest gene-environment interaction in the etiology of schizophrenia spectrum disorders, but the molecular evidence is scarce. Here, by analyzing the main and joint associations of polygenic risk score for schizophrenia (PRS-SCZ) and environmental exposures in 1,699 patients with a diagnosis of schizophrenia spectrum disorders and 1,542 unrelated controls with no lifetime history of a diagnosis of those disorders, we provide further evidence for gene-environment interaction in schizophrenia. Evidence was found for additive interaction of molecular genetic risk state for schizophrenia (binary mode of PRS-SCZ above 75% of the control distribution) with the presence of lifetime regular cannabis use and exposure to early-life adversities (sexual abuse, emotional abuse, emotional neglect, and bullying), but not with the presence of hearing impairment, season of birth (winter birth), and exposure to physical abuse or physical neglect in childhood. The sensitivity analyses replacing the a priori PRS-SCZ at 75% with alternative cut-points (50% and 25%) confirmed the additive interaction. Our results suggest that the etiopathogenesis of schizophrenia involves genetic underpinnings that act by making individuals more sensitive to the effects of some environmental exposures.

From Infection to the Microbiome: An Evolving Role of Microbes in Schizophrenia

The study of microorganisms such as bacteria, viruses, archaea, fungi, and protozoa in the context of psychiatric disorders may be surprising to some. This intersection of disciplines, however, has a rich history and is currently revitalized by newfound functions of the microbiome and the gut-brain axis in human diseases. Schizophrenia, in particular, fits this model as a disorder with gene and environmental roots that may be anchored in the immune system. In this context, the combination of a precisely timed pathogen exposure in a person with genetically encoded altered immunity may have especially destructive consequences for the central nervous system (CNS). Furthermore, significant components of immunity, such as the development of the immune response and the concept of immune tolerance, are largely dictated by the commensal residents of the microbiome. When this community of microbes is imbalanced, perhaps as the result of a pathogen invasion, stress, or immune gene deficiency, a pathological cycle of localized inflammation, endothelial barrier compromise, translocation of gut-derived products, and systemic inflammation may ensue. If these pathologies enable access of gut and microbial metabolites and immune molecules to the CNS across the blood-brain barrier (BBB), and studies of the gut-brain axis support this hypothesis, a worsening of cognitive deficits and psychiatric symptoms is predicted to occur in susceptible individuals with schizophrenia. In this chapter, we review the role of microbes in various stages of this model and how these organisms may contribute to documented phenotypes of schizophrenia. An increased understanding of the role of pathogens and the microbiome in psychiatric disorders will better guide the development of microbial and immune-based therapeutics for disease prevention and treatment.

Deciphering microbiome and neuroactive immune gene interactions in schizophrenia

The body's microbiome represents an actively regulated network of novel mechanisms that potentially underlie the etiology and pathophysiology of a wide range of diseases. For complex brain disorders such as schizophrenia, understanding the cellular and molecular pathways that intersect the bidirectional gut-brain axis is anticipated to lead to new methods of treatment. The means by which the microbiome might differ across neuropsychiatric and neurological disorders are not known. Brain disorders as diverse as schizophrenia, major depression, Parkinson's disease and multiple sclerosis appear to share a common pathology of an imbalanced community of commensal microbiota, often measured in terms of a leaky gut phenotype accompanied by low level systemic inflammation. While environmental factors associated with these disease states might contribute to intestinal pathologies, products from a perturbed microbiome may also directly promote specific signs, symptoms and etiologies of individual disorders. We hypothesize that in schizophrenia, it is the putatively unique susceptibility related to genes that modulate the immune system and the gut-brain pleiotropy of these genes which leads to a particularly neuropathological response when challenged by a microbiome in dysbiosis. Consequences from exposure to this dysbiosis may occur during pre- or post-natal time periods and thus may interfere with normal neurodevelopment in those who are genetically predisposed. Here, we review the evidence from the literature which supports the idea that the intersection of the microbiome and immune gene susceptibility in schizophrenia is relevant etiologically and for disease progression. Figuring prominently at both ends of the gut-brain axis and at points in between are proteins encoded by genes found in the major histocompatibility complex (MHC), including select MHC as well as non-MHC complement pathway genes.

Autoimmune phenotypes in schizophrenia reveal novel treatment targets

Typical and atypical antipsychotics are the first-line treatments for schizophrenia, but these classes of drugs are not universally effective, and they can have serious side effects that impact compliance. Antipsychotic drugs generally target the dopamine pathways with some variation. As research of schizophrenia pathophysiology has shifted away from a strictly dopamine-centric focus, the development of new pharmacotherapies has waned. A field of inquiry with centuries-old roots is gaining traction in psychiatric research circles and may represent a new frontier for drug discovery in schizophrenia. At the forefront of this investigative effort is the immune system and its many components, pathways and phenotypes, which are now known to actively engage the brain. Studies in schizophrenia reveal an intricate association of environmentally-driven immune activation in concert with a disrupted genetic template. A consistent conduit through this gene-environmental milieu is the gut-brain axis, which when dysregulated can generate pathological autoimmunity. In this review, we present epidemiological and biochemical evidence in support of an autoimmune component in schizophrenia and depict gut processes and a dysbiotic microbiome as a source and perpetuator of autoimmune dysfunction in the brain. Within this framework, we review the role of infectious agents, inflammation, gut dysbioses and autoantibody propagation on CNS pathologies such as neurotransmitter receptor hypofunction and complement pathway-mediated synaptic pruning. We then review the new pharmacotherapeutic horizon and novel agents directed to impact these pathological conditions. At the core of this discourse is the understanding that schizophrenia is etiologically and pathophysiologically heterogeneous and thus its treatment requires individualized attention with disease state variants diagnosed with objective biomarkers.

Interactions Between Variation in Candidate Genes and Environmental Factors in the Etiology of Schizophrenia and Bipolar Disorder: a Systematic Review

Schizophrenia and bipolar disorder (BD) are complex and multidimensional disorders with high heritability rates. The contribution of genetic factors to the etiology of these disorders is increasingly being recognized as the action of multiple risk variants with small effect sizes, which might explain only a minor part of susceptibility. On the other site, numerous environmental factors have been found to play an important role in their causality. Therefore, in recent years, several studies focused on gene × environment interactions that are believed to bridge the gap between genetic underpinnings and environmental insults. In this article, we performed a systematic review of studies investigating gene × environment interactions in BD and schizophrenia spectrum phenotypes. In the majority of studies from this field, interacting effects of variation in genes encoding catechol-O-methyltransferase (COMT), brain-derived neurotrophic factor (BDNF), and FK506-binding protein 5 (FKBP5) have been explored. Almost consistently, these studies revealed that polymorphisms in COMT, BDNF, and FKBP5 genes might interact with early life stress and cannabis abuse or dependence, influencing various outcomes of schizophrenia spectrum disorders and BD. Other interactions still require further replication in larger clinical and non-clinical samples. In addition, future studies should address the direction of causality and potential mechanisms of the relationship between gene × environment interactions and various categories of outcomes in schizophrenia and BD.

Interaction between compound genetic risk for schizophrenia and high birth weight contributes to social anhedonia and schizophrenia in women

Schizophrenia is a highly heritable disease, but despite extensive study, its genetic background remains unresolved. The lack of environmental measures in genetic studies may offer some explanation. In recent Finnish studies, high birth weight was found to increase the risk for familial schizophrenia. We examined the interaction between a polygenic risk score for schizophrenia and high birth weight on social anhedonia and schizophrenia in a general population birth cohort. The study sample included 4223 participants from the 1966 Northern Finland Birth Cohort. As a replication sample we used 256 participants from a systematically collected sample of Finnish schizophrenia families. The polygenic risk score comprised of variants published in the large genome-wide meta-analysis for schizophrenia. We found the association between the polygenic risk score and social anhedonia stronger among those with high birth weight, and the same phenomenon was seen for schizophrenia among women, suggesting a gene-environment interaction. Similar results were found within the replication sample. Our results suggest a role for gene-environment interactions in assessing the risk of schizophrenia. Failure to take environmental effects into account may be one of the reasons why identifying significant SNPs for schizophrenia in genome-wide studies has been challenging.

The Gut Microbiota and the Emergence of Autoimmunity: Relevance to Major Psychiatric Disorders

BACKGROUND

Autoimmune phenotypes are prevalent in major psychiatric disorders. Disequilibria of cellular processes occurring in the gastrointestinal (GI) tract likely contribute to immune dysfunction in psychiatric disorders. As the venue of a complex community of resident microbes, the gut in a homeostatic state equates with a functional digestive system, cellular barrier stability and properly regulated recognition of self and non-self antigens. When gut processes become disrupted as a result of environmental or genetic factors, autoimmunity may ensue.

METHODS

Here, we review the issues pertinent to autoimmunity and the microbiome in psychiatric disorders and show that many of the reported immune risk factors for the development of these brain disorders are in fact related and consistent with dysfunctions occurring in the gut. We review the few human microbiome studies that have been done in people with psychiatric disorders and supplement this information with mechanistic data gleaned from experimental rodent studies.

RESULTS

These investigations demonstrate changes in behavior and brain biochemistry directly attributable to alterations in the gut microbiome. We present a model by which autoantigens are produced by extrinsicallyderived food and microbial factors bound to intrinsic components of the gut including receptors present in the enteric nervous system.

CONCLUSION

This new focus on examining activities outside of the CNS for relevance to the etiology and pathophysiology of psychiatric disorders may require new modalities or a re-evaluation of pharmaceutical targets found in peripheral systems.

Post-zygotic genomic changes in glutamate and dopamine pathway genes may explain discordance of monozygotic twins for schizophrenia

Background

Monozygotic twins are valuable in assessing the genetic vs environmental contribution to diseases. In the era of complete genome sequences, they allow identification of mutational mechanisms and specific genes and pathways that offer predisposition to the development of complex diseases including schizophrenia.

Methods

We sequenced the complete genomes of two pairs of monozygotic twins discordant for schizophrenia (MZD), including one representing a family tetrad. The family specific complete sequences have allowed identification of post zygotic mutations between MZD genomes. It allows identification of affected genes including relevant network and pathways that may account for the diseased state in pair specific patient.

Results

We found multiple twin specific sequence differences between co-twins that included small nucleotides [single nucleotide variants (SNV), small indels and block substitutions], copy number variations (CNVs) and structural variations. The genes affected by these changes belonged to a number of canonical pathways, the most prominent ones are implicated in schizophrenia and related disorders. Although these changes were found in both twins, they were more frequent in the affected twin in both pairs. Two specific pathway defects, glutamate receptor signaling and dopamine feedback in cAMP signaling pathways, were uniquely affected in the two patients representing two unrelated families.

Conclusions

We have identified genome-wide post zygotic mutations in two MZD pairs affected with schizophrenia. It has allowed us to use the threshold model and propose the most likely cause of this disease in the two patients studied. The results support the proposition that each schizophrenia patient may be unique and heterogeneous somatic de novo events may contribute to schizophrenia threshold and discordance of the disease in monozygotic twins.

Electronic supplementary material

The online version of this article (10.1186/s40169-017-0174-1) contains supplementary material, which is available to authorized users.

The complement system: a gateway to gene-environment interactions in schizophrenia pathogenesis

The pathogenesis of schizophrenia is considered to be multi-factorial, with likely gene-environment interactions (GEI). Genetic and environmental risk factors are being identified with increasing frequency, yet their very number vastly increases the scope of possible GEI, making it difficult to identify them with certainty. Accumulating evidence suggests a dysregulated complement pathway among the pathogenic processes of schizophrenia. The complement pathway mediates innate and acquired immunity, and its activation drives the removal of damaged cells, autoantigens and environmentally derived antigens. Abnormalities in complement functions occur in many infectious and autoimmune disorders that have been linked to schizophrenia. Many older reports indicate altered serum complement activity in schizophrenia, though the data are inconclusive. Compellingly, recent genome-wide association studies suggest repeat polymorphisms incorporating the complement 4A (C4A) and 4B (C4B) genes as risk factors for schizophrenia. The C4A/C4B genetic associations have re-ignited interest not only in inflammation-related models for schizophrenia pathogenesis, but also in neurodevelopmental theories, because rodent models indicate a role for complement proteins in synaptic pruning and neurodevelopment. Thus, the complement system could be used as one of the 'staging posts' for a variety of focused studies of schizophrenia pathogenesis. They include GEI studies of the C4A/C4B repeat polymorphisms in relation to inflammation-related or infectious processes, animal model studies and tests of hypotheses linked to autoimmune diseases that can co-segregate with schizophrenia. If they can be replicated, such studies would vastly improve our understanding of pathogenic processes in schizophrenia through GEI analyses and open new avenues for therapy.

Modelling gene-environment interaction in first episodes of psychosis

INTRODUCTION

Recent research demonstrates the heterogeneous etiology of psychotic disorders, where gen-environment (GxE) interaction plays a key role. Large genetic studies have linked many genetic variants with schizophrenia, but each variant is only associated with a small effect and the GxE interaction contribution has not been evaluated.

METHODS

The PEPs Project was designed to carefully collect a large amount of genetic and environmental exposure data of 335 FEP patients and 253 matched healthy controls.780single-nucleotide polymorphisms (from 159 candidate genes)and 16 environmental variables previously reported as the main psychosis non-genetic risk factors were analyzed together using entropy-based measures of information gain.

RESULTS

Our analyses identified an interaction between nine SNPs and the exposition to the environmental risk factors of psychosis, showing a clear enrichment of genes linked to serotonin neurotransmission and neurodevelopmental processes.

CONCLUSIONS

This study has allowed the identification of several GxE-environment interactions involved in the risk of presenting a FEP. Our results highlight the importance of serotonin neurotransmission interacting with certain environmental stimuli. The serotoninergic system may be playing a key role in the regulatory network of stress and other systems implicated in the emergence and development of psychotic disorders.

Gene-environment interaction and psychiatric disorders: Review and future directions

Empirical studies suggest that psychiatric disorders result from a complex interplay between genetic and environmental factors. Most evidence for such gene-environment interaction (GxE) is based on single candidate gene studies conducted from a Diathesis-Stress perspective. Recognizing the short-comings of candidate gene studies, GxE research has begun to focus on genome-wide and polygenic approaches as well as drawing on different theoretical concepts underlying GxE, such as Differential Susceptibility. After reviewing evidence from candidate GxE studies and presenting alternative theoretical frameworks underpinning GxE research, more recent approaches and findings from whole genome approaches are presented. Finally, we suggest how future GxE studies may unpick the complex interplay between genes and environments in psychiatric disorders.

Genetics of schizophrenia: A consensus paper of the WFSBP Task Force on Genetics

OBJECTIVES

Schizophrenia is a severe psychiatric disease affecting about 1% of the general population. The relative contribution of genetic factors has been estimated to be up to 80%. The mode of inheritance is complex, non-Mendelian, and in most cases involving the combined action of large numbers of genes.

METHODS

This review summarises recent efforts to identify genetic variants associated with schizophrenia detected, e.g., through genome-wide association studies, studies on copy-number variants or next-generation sequencing.

RESULTS

A large, new body of evidence on genetics of schizophrenia has accumulated over recent years. Many new robustly associated genetic loci have been detected. Furthermore, there is consensus that at least a dozen microdeletions and microduplications contribute to the disease. Genetic overlap between schizophrenia, other psychiatric disorders, and neurodevelopmental syndromes raised new questions regarding the current classification of psychiatric and neurodevelopmental diseases.

CONCLUSIONS

Future studies will address especially the functional characterisation of genetic variants. This will hopefully open the doors to our understanding of the pathophysiology of schizophrenia and other related diseases. Complementary, integrated systems biology approaches to genomics, transcriptomics, proteomics and metabolomics may also play crucial roles in enabling a precision medicine approach to the treatment of individual patients.

[Genetics and epigenetics of schizophrenia and other psychoses]

Schizophrenia and other psychoses are categorical psychiatric diagnoses corresponding to frequent and heterogeneous disorders. Their physiopathology still remains largely unknown despite numerous recent advances. In particular, the last decade has identified different types of genetic variants, thanks to emergence of high-throughput methods. These methods allow both the identification of rare variants with a large effect such as punctual mutations or copy-number variants and the identification of frequent variants with a limited effect such as polymorphisms. Many impacted genes have been identified showing a very high genetic heterogeneity of psychoses. These genes are overrepresented in synaptic and neurotransmission pathways. Only a small fraction of psychoses could be easily explained by genetics but this screening in clinical practice is important as it can lead to therapeutic challenge or genetic counselling. Nowadays, it is clear that the pathophysiology of the psychoses can only be understood by an integrative approach taking into account the interaction between genes and environment. This interaction could be mediated by the epigenome defined as the modification of gene expression without changes in DNA sequence. Epigenome is stable but could be modified by environmental factors. Several epigenetic mechanisms have been studied in psychosis, in particular the DNA methylation, the modification of histones and the microRNA. All of these mechanisms are under regulation by genetic factors and variants in these epigenetic-involved genes and cofactors have been also associated with schizophrenia. Thus, pathophysiology of psychosis is complex and morestudiesare needed before definitive conclusions. Altogether, the recent advances in the genetics and epigenetics of psychosis are promising and could open the way to a recategorization of these disorders as well as the identification of new therapeutic targets.

Association between ErbB4 single nucleotide polymorphisms and susceptibility to schizophrenia: A meta-analysis of case-control studies

BACKGROUND

Accumulating studies have reported inconsistent association between ErbB4 single nucleotide polymorphisms (SNPs) and predisposition to schizophrenia. To better interpret this issue, here we conducted a meta-analysis using published case-control studies.

METHODS

We conducted a systematic search of MEDLINE (Pubmed), Embase (Ovid), Web of Science (Thomson-Reuters) to identify relevant references. The association between ErbB4 SNPs and schizophrenia was assessed by odds ratios (ORs) and 95% confidence intervals (CIs). Between-study heterogeneity was evaluated by I squared (I) statistics and Cochran's Q test. To appraise the stability of results, we employed sensitivity analysis by omitting 1 single study each time. To assess the potential publication bias, we conducted trim and fill analysis.

RESULTS

Seven studies published in English comprising 3162 cases and 4264 controls were included in this meta-analysis. Meta-analyses showed that rs707284 is statistically significantly associated with schizophrenia susceptibility among Asian and Caucasian populations under the allelic model (OR = 0.91, 95% CI: 0.83-0.99, P = 0.035). Additionally, a marginal association (P < 0.1) was observed between rs707284 and schizophrenia risk among Asian and Caucasian populations under the recessive (OR = 0.85, 95% CI: 0.72-1.01, P = 0.065) and homozygous (OR = 0.84, 95% CI: 0.68-1.03, P = 0.094) models. In the Asian subgroup, rs707284 was also noted to be marginally associated with schizophrenia under the recessive model (OR = 0.84, 95% CI: 0.70-1.00, P = 0.053). However, no statistically significant association was found between rs839523, rs7598440, rs3748962, and rs2371276 and schizophrenia risk.

CONCLUSION

This meta-analysis suggested that rs707284 may be a potential ErbB4 SNP associated with susceptibility to schizophrenia. Nevertheless, due to the limited sample size in this meta-analysis, more large-scale association studies are still needed to confirm the results.

Interaction Effects of Season of Birth and Cytokine Genes on Schizotypal Traits in the General Population

Literature suggests that the effect of winter birth on vulnerability to schizophrenia might be mediated by increased expression of proinflammatory cytokines due to prenatal infection and its inadequate regulation by anti-inflammatory factors. As the response of the immune system depends on genotype, this study assessed the interaction effects of cytokine genes and season of birth (SOB) on schizotypy measured with the Schizotypal Personality Questionnaire (SPQ-74). We searched for associations of IL1B rs16944, IL4 rs2243250, and IL-1RN VNTR polymorphisms, SOB, and their interactions with the SPQ-74 total score in a sample of 278 healthy individuals. A significant effect of the IL4 X SOB interaction was found, p = 0.007 and η² = 0.028. We confirmed this effect using an extended sample of 373 individuals. Homozygotes CC born in winter showed the highest SPQ total score and differed significantly from winter-born T allele carriers, p = 0.049. This difference was demonstrated for cognitive-perceptual and disorganized but not interpersonal dimensions. The findings are consistent with the hypothesis that the cytokine genes by SOB interaction can influence variability of schizotypal traits in the general population. The IL4 T allele appeared to have a protective effect against the development of positive and disorganized schizotypal traits in winter-born individuals.

Adversity in childhood linked to elevated striatal dopamine function in adulthood

Childhood adversity increases the risk of psychosis in adulthood. Theoretical and animal models suggest that this effect may be mediated by increased striatal dopamine neurotransmission. The primary objective of this study was to examine the relationship between adversity in childhood and striatal dopamine function in early adulthood. Secondary objectives were to compare exposure to childhood adversity and striatal dopamine function in young people at ultra high risk (UHR) of psychosis and healthy volunteers. Sixty-seven young adults, comprising 47 individuals at UHR for psychosis and 20 healthy volunteers were recruited from the same geographic area and were matched for age, gender and substance use. Presynaptic dopamine function in the associative striatum was assessed using 18F-DOPA positron emission tomography. Childhood adversity was assessed using the Childhood Experience of Care and Abuse questionnaire. Within the sample as a whole, both severe physical or sexual abuse (T63=2.92; P=0.005), and unstable family arrangements (T57=2.80; P=0.007) in childhood were associated with elevated dopamine function in the associative striatum in adulthood. Comparison of the UHR and volunteer subgroups revealed similar incidence of childhood adverse experiences, and there was no significant group difference in dopamine function. This study provides evidence that childhood adversity is linked to elevated striatal dopamine function in adulthood.

Gene-environment interactions in a rat model of depression. Maternal separation affects neurotensin in selected brain regions

Although the etiology of major psychiatric disorders has not been elucidated, accumulating evidence indicates that both genetic and early environmental factors play a role. We have previously demonstrated behavioral and neurochemical changes both in non-manipulated genetic rat models of depression, such as Flinders Sensitive Line (FSL) and Fawn Hooded (FH), and in normal rats following maternal separation (MS). The aim of the present study was to extend this work by exploring whether neurotensin (NT), a peptide implicated in several psychiatric disorders, is altered in a new animal model based on gene - environment interactions. More specifically, we used the FSL rats as a genetic model of depression and the Flinders Resistant Line (FRL) as controls and subjected them to MS. Pups randomly assigned to the MS procedure were separated from the dam as a litter for 180min daily between postnatal day 2 to 14. On postnatal day 90, rats were weighed and sacrificed by a two second high energy focused microwave irradiation and several brain regions were obtained by micropuncture. Neurotensin-like immunoreactivity (NT-LI) was measured by radioimmunoassay (RIA). The results showed that the FSL rats compared to the FRL rats have higher baseline NT-LI concentrations in the temporal cortex and periaqueductal gray and a markedly different response to maternal separation. The only observed change following maternal separation in the FRL rats was an NT-LI increase in the periaqueductal gray. In contrast, in the FSL significant increases were found in the nucleus accumbens, hippocampus, and entorhinal cortex and a decrease was seen in the temporal cortex after MS. The present study revealed baseline regional differences in NT-LI concentrations between the FSL and FRL strains and demonstrated that early MD differentially affects the two strains. The relevance of these alterations for depression as well as possible mechanisms underlying this gene-environment interaction are discussed.

Autoimmune diseases, gastrointestinal disorders and the microbiome in schizophrenia: more than a gut feeling

Autoimmunity, gastrointestinal (GI) disorders and schizophrenia have been associated with one another for a long time. This paper reviews these connections and provides a context by which multiple risk factors for schizophrenia may be related. Epidemiological studies strongly link schizophrenia with autoimmune disorders including enteropathic celiac disease. Exposure to wheat gluten and bovine milk casein also contribute to non-celiac food sensitivities in susceptible individuals. Co-morbid GI inflammation accompanies humoral immunity to food antigens, occurs early during the course of schizophrenia and appears to be independent from antipsychotic-generated motility effects. This inflammation impacts endothelial barrier permeability and can precipitate translocation of gut bacteria into systemic circulation. Infection by the neurotropic gut pathogen, Toxoplasma gondii, will elicit an inflammatory GI environment. Such processes trigger innate immunity, including activation of complement C1q, which also functions at synapses in the brain. The emerging field of microbiome research lies at the center of these interactions with evidence that the abundance and diversity of resident gut microbiota contribute to digestion, inflammation, gut permeability and behavior. Dietary modifications of core bacterial compositions may explain inefficient gluten digestion and how immigrant status in certain situations is a risk factor for schizophrenia. Gut microbiome research in schizophrenia is in its infancy, but data in related fields suggest disease-associated altered phylogenetic compositions. In summary, this review surveys associative and experimental data linking autoimmunity, GI activity and schizophrenia, and proposes that understanding of disrupted biological pathways outside of the brain can lend valuable information regarding pathogeneses of complex, polygenic brain disorders.

Effects of fingolimod administration in a genetic model of cognitive deficits

Notwithstanding recent advances, cognitive impairments are among the most difficult-to-treat symptoms in neuropsychiatric disorders. Deficits in information processing contributing to memory and sociability impairments are found across neuropsychiatric-related disorders. Previously, we have shown that mutations in the DTNBP1 gene (encoding dystrobrevin-binding protein 1 [dysbindin-1]) lead to abnormalities in synaptic glutamate release in the prefrontal cortex (PFC) and hippocampus and to cognitive deficits; glutamatergic transmission is important for cortical recurrent excitation that allows information processing in the PFC. To investigate possible means of restoring glutamate release and improving cognitive impairments, we assess the effects of increasing endogenous levels of brain-derived neurotrophic factor (BDNF) in a dysbindin-1-deficient mouse model. Increasing endogenous levels of BDNF may aid in remediating cognitive deficits, given the roles of BDNF in synaptic transmission, plasticity, and neuroprotection. To increase BDNF, we use a novel strategy, repeated intraperitoneal injections of fingolimod (Gilenya). Sphingolipids have recently been shown to have therapeutic value in several neurology-related disorders. Both wild-type (WT) and mutant (MUT) genotypes were tested for sociability and recognition memory, followed by measuring endogenous BDNF levels and presynaptic [Ca²⁺ ]_i within the PFC. Both genotypes were treated for 1 week with either saline or fingolimod. Relative to WT mice, MUT mice demonstrated impairments in sociability and recognition memory and lower presynaptic calcium. After fingolimod treatment, MUT mice exhibited significant improvements in sociability and recognition memory and increases in presynaptic calcium and endogenous concentrations of BDNF. These results show promise for counteracting the cognitive impairments seen in neuropsychiatric disorders and may shed light on the role of dysbindin-1. © 2016 Wiley Periodicals, Inc.

Nicotine ameliorates schizophrenia-like cognitive deficits induced by maternal LPS exposure: a study in rats

Maternal exposure to infectious agents is a predisposing factor for schizophrenia with associated cognitive deficits in offspring. A high incidence of smoking in these individuals in adulthood might be, at least in part, due to the cognitive-enhancing effects of nicotine. Here, we have used prenatal exposure to maternal lipopolysaccharide (LPS, bacterial endotoxin) at different time points as a model for cognitive deficits in schizophrenia to determine whether nicotine reverses any associated impairments. Pregnant rats were treated subcutaneously with LPS (0.5 mg/kg) at one of three neurodevelopmental time periods [gestation days (GD) 10-11, 15-16, 18-19]. Cognitive assessment in male offspring commenced in early adulthood [postnatal day (PND) 60] and included: prepulse inhibition (PPI), latent inhibition (LI) and delayed non-matching to sample (DNMTS). Following PND 100, daily nicotine injections (0.6 mg/kg, subcutaneously) were administered, and animals were re-tested in the same tasks (PND 110). Only maternal LPS exposure early during fetal neurodevelopment (GD 10-11) resulted in deficits in all tests compared to animals that had been prenatally exposed to saline at the same gestational time point. Repeated nicotine treatment led to global (PPI) and selective (LI) improvements in performance. Early but not later prenatal LPS exposure induced consistent deficits in cognitive tests with relevance for schizophrenia. Nicotine reversed the LPS-induced deficits in selective attention (LI) and induced a global enhancement of sensorimotor gating (PPI).

Neglect and hereditary risk: Their relative contribution to schizophrenia with negative symptomatology

BACKGROUND

There is evidence that genetic and environmental stressors contribute to the genesis of schizophrenia. However, the relevant impact of each factor remains unclear. We tested for an interactive effect between childhood neglect and family history of serious mental illness. Data were further analyzed for a possible connection to type of schizophrenic symptoms.

SAMPLING/METHODS

Data for the study are taken from the medical records of 641 patients with schizophrenia from a large state hospital in the northeastern United States. Clinical assessments were divided into positive and negative symptomatology through application of the Scale for the Assessment of Negative Symptoms (SANS), the Scale for the Assessment of Positive Symptoms (SAPS) and the Positive and Negative Syndrome Scale (PANSS). Detailed information about childhood neglect and family history of serious mental illness was obtained through Social Service Assessment interviews at intake and during hospital stay.

RESULTS

Among clients with no family history of mental illness, childhood neglect does not meaningfully affect the risk of negative versus positive schizophrenia. For clients with such history, on the other hand, neglect significantly raises the risk of schizophrenia with negative symptomatology.

CONCLUSION

Our central finding is that risk for negative symptoms of schizophrenia are elevated by childhood neglect combined with a history of serious mental illness within the family. This is the only report to combine schizophrenic symptoms, familial risk and childhood neglect to date. Implications for primary prevention and treatment are discussed.

Effective Strategies for Nurses Empowering Clients With Schizophrenia: Medication Use as a Tool in Recovery

Clients with schizophrenia require maintenance treatment with antipsychotic medication and psychosocial therapy to maintain symptom control. Rates of medication adherence or follow-through are low in clients with schizophrenia. This increases the risk of relapse and contributes to poor quality of life. As educators and advisers, psychiatric nurses can collaborate with clients to improve adherence and other outcomes using shared decision-making techniques and tools that engage and empower clients to actively participate in decisions about their treatment. This article outlines effective strategies used by psychiatric nurses to improve outcomes in clients with schizophrenia and uses a case example for demonstrating this strategy in a client with schizophrenia.

Age of Onset in Schizophrenia Spectrum Disorders: Complex Interactions between Genetic and Environmental Factors

In this study we evaluated the role of a candidate gene for major psychosis, Sialyltransferase (ST8SIA2), in the risk to develop a schizophrenia spectrum disorders, taking into account exposure to stressful life events (SLEs). Eight polymorphisms (SNPs) were tested in 94 Schizophreniainpatients and 176 healthy controls. Schizophrenia patients were also evaluated for SLEs in different life periods. None of the SNPs showed association with schizophrenia. Nevertheless, when crossing genetic variants with childhood SLEs, we could observe trends of interaction with age of onset. Though several limitations, our results support a protective role of ST8SIA2 in individuals exposed to moderate childhood stress.

Epigenetic Treatment of Neuropsychiatric Disorders: Autism and Schizophrenia

Neuropsychiatric disorders are a heterogeneous group of conditions that often share underlying mitochondrial dysfunction and biological pathways implicated in their pathogenesis, progression, and treatment. To date, these disorders have proven notoriously resistant to molecular-targeted therapies, and clinical options are relegated to interventional types, which do not address the core symptoms of the disease. In this review, we discuss emerging epigenetic-driven approaches using novel acylcarnitine esters (carnitinoids) that act on master regulators of antioxidant and cytoprotective genes and mitophagic pathways. These carnitinoids are actively transported, mitochondria-localizing, biomimetic coenzyme A surrogates of short-chain fatty acids, which inhibit histone deacetylase and may reinvigorate synaptic plasticity and protect against neuronal damage. We outline these neuroprotective effects in the context of treatment of neuropsychiatric disorders such as autism spectrum disorder and schizophrenia.

BDNF Val66Met and clinical response to antipsychotic drugs: A systematic review and meta-analysis

BACKGROUND

The polymorphic brain-derived neurotrophic factor (BDNF) gene has been postulated to be involved in inter-individual variability response to antipsychotic drugs.

PURPOSE

To perform a qualitative and quantitative synthesis of studies evaluating the influence of BDNF genetic variation on clinical response to antipsychotics.

METHODS

The review protocol was published in the PROSPERO database (Reg. n(o) CRD42015024614). A comprehensive search was performed through PubMed, Web of Knowledge and Cochrane databases up to July 2015. The methodological quality of identified studies was assessed using the MINORS criteria. Publication bias was estimated and potential sources of heterogeneity were investigated via meta-regression, subgroup and sensitivity analyses.

RESULTS

Nine studies including a total of 2461 antipsychotic-treated patients fulfilled inclusion criteria for meta-analysis of BDNF Val66Met. Using the random-effects model, the pooled results showed no significant association with antipsychotic response for the dominant (Met carriers vs Val/Val, OR: 0.93, 95% CI: 0.72-1.19, P=0.55), codominant (Met/Met vs Val/Val, OR: 0.82, 95% CI: 0.59-1.15, P=0.25), recessive (Met/Met vs Val carriers, OR: 0.81, 95% CI 0.60-1.10, P=0.18) or the allelic contrast (Met vs Val, OR: 0.92, 95% CI 0.76-1.10, P=0.34). Visual inspection of funnel plots and further evaluation with Egger's test did not suggest evidence of publication bias. Despite lack of significant heterogeneity in most comparisons, no evidence of association also emerged in the subgroup and sensitivity analyses conducted.

CONCLUSION

The present meta-analysis excludes a clinically relevant effect of BDNF Val66Met on antipsychotic drug response per se. Nevertheless, further investigation is still needed to clarify in well-designed, large sample-based studies, the impact of BDNF haplotypes containing the Val66Met polymorphism.

Role of Immune and Autoimmune Dysfunction in Schizophrenia

In this chapter, we review data in support of the concept that immune system dysregulation is the most plausible explanation that reconciles gene by environmental interactions in schizophrenia. Early investigations of this topic demonstrated aspects of aberrant activation of humoral immunity, including autoimmunity, associated with schizophrenia, whereas current research efforts have expanded this theme to include elements of innate immunity. Advances in our understanding of inflammation and molecules of both the adaptive and innate immune system and their functional roles in standard brain physiology provide an important context by which schizophrenia might arise as the result of the coupling of immune and neurodevelopmental dysregulation.

Salivary cortisol in early psychosis: New findings and meta-analysis

BACKGROUND

Schizophrenia is a multifactorial disorder and environmental risk factors for it might contribute to hypothalamo-pituitary-adrenal axis (HPA) dysregulation. While increased cortisol levels have been reported in schizophrenia, as well as in early psychosis (compared to healthy controls), a crucial unresolved issue is whether elevated cortisol levels could be related to the distress of an emerging illness, rather than being specific to psychosis. Here, we report new findings from the first French cohort of young help-seekers (ICAAR) including ultra-high risk subjects (UHR), first-episode of psychosis (FEP) and non at-risk help seekers controls (HSC), followed by a meta-analysis of all available reports on salivary basal cortisol levels in early psychosis (UHR and FEP).

METHODS

In the ICAAR study, 169 individuals (15-30 years old) had their basal cortisol levels sampled and they were categorized (at baseline) as either UHR, FEP, or HSC using the criteria of the Comprehensive Assessment of At-Risk Mental States (CAARMS). The three groups were compared at baseline, and the UHR and HSC individuals were also included in a one-year longitudinal follow-up. UHRs who converted to psychosis at the follow up (UHR-P) were compared to non-converters (UHR-NP). We also performed a meta-analysis from case-control studies with basal salivary measures of cortisol, drawing from a systematic bibliographic search using the keywords 'cortisol', 'glucocorticoid', 'HPA' with 'UHR', 'CHR', 'at-risk mental state', 'schizotypal ', 'prodromal schizophrenia', 'first-episode psychosis', 'first episode schizophrenia', 'newly diagnosed schizophrenia', 'recent onset schizophrenia' [in Medline, Web of Knowledge (WOS), EBSCO], followed by a systematic screening of the resulting articles.

RESULTS

Basal cortisol levels were not significantly different between UHR, FEP, and HSC controls in the ICAAR cohort. Interestingly, initial cortisol levels were correlated with positive symptoms at the one year follow-up in the ICAAR cohort. The meta-analysis revealed a significant elevation of the salivary basal cortisol levels in UHR individuals compared to controls (8 studies--1060 individuals), but not between FEP and controls (6 studies--441 individuals). Indirect comparison of salivary basal cortisol levels between UHR and FEP did not yield significant differences. Finally, no differences were detected between the baseline cortisol of UHR-P and UHR-NP (4 studies--301 individuals).

CONCLUSION

The meta-analysis (including new data) indicates that basal cortisol levels were increased in UHR compared to controls, but FEP levels were not different from UHR or controls. Many confounding factors could decrease the effect size in FEP especially medication intake. Taken together with our new results (which made use of help-seeker controls, and not merely healthy controls), the findings indicate that basal cortisol levels may not be a reliable biomarker for early psychosis. Further studies are needed to clarify the precise role of the HPA axis in psychotic conversion.

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.

An interaction between NDE1 and high birth weight increases schizophrenia susceptibility

Pre- and perinatal environmental factors have been shown to increase schizophrenia risk particularly when combined with genetic liability. The investigation of specific gene environment interactions in the etiology of psychiatric disorders has gained momentum. We used multivariate GEE regression modeling to investigate the interaction between genes of the DISC1 pathway and birth weight, in relation to schizophrenia susceptibility in a Finnish schizophrenia family cohort. The study sample consisted of 457 subjects with both genotype and birth weight information. Gender and place of birth were adjusted for in the models. We found a significant interaction between birth weight and two NDE1 markers in relation to increased schizophrenia risk: a four SNP haplotype spanning NDE1 (b=1.26, SE=0.5, p=0.012) and one of its constituent SNPs rs4781678 (b=1.33, SE=0.51, p=0.010). Specifically, high birth weight (>4000g) was associated with increased schizophrenia risk among subjects homozygous for the previously identified risk alleles. The study was based on a family study sample with high genetic loading for schizophrenia and thus our findings cannot directly be generalized as representing the general population. Our results suggest that the functions mediated by NDE1 during the early stages of neurodevelopment are susceptible to the additional disruptive effects of pre- and perinatal environmental factors associated with high birth weight, augmenting schizophrenia susceptibility.

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.

Antipsychotic drugs attenuate aberrant DNA methylation of DTNBP1 (dysbindin) promoter in saliva and post-mortem brain of patients with schizophrenia and Psychotic bipolar disorder

Due to the lack of genetic association between individual genes and schizophrenia (SCZ) pathogenesis, the current consensus is to consider both genetic and epigenetic alterations. Here, we report the examination of DNA methylation status of DTNBP1 promoter region, one of the most credible candidate genes affected in SCZ, assayed in saliva and post-mortem brain samples. The Illumina DNA methylation profiling and bisulfite sequencing of representative samples were used to identify methylation status of the DTNBP1 promoter region. Quantitative methylation specific PCR (qMSP) was employed to assess methylation of DTNBP1 promoter CpGs flanking a SP1 binding site in the saliva of SCZ patients, their first-degree relatives and control subjects (30, 15, and 30/group, respectively) as well as in post-mortem brains of patients with SCZ and bipolar disorder (BD) versus controls (35/group). qRT-PCR was used to assess DTNBP1 expression. We found DNA hypermethylation of DTNBP1 promoter in the saliva of SCZ patients (∼12.5%, P = 0.036), particularly in drug-naïve patients (∼20%, P = 0.011), and a trend toward hypermethylation in their first-degree relatives (P = 0.085) versus controls. Analysis of post-mortem brain samples revealed an inverse correlation between DTNBP1 methylation and expression, and normalization of this epigenetic change by classic antipsychotic drugs. Additionally, BD patients with psychotic depression exhibited higher degree of methylation versus other BD patients (∼80%, P = 0.025). DTNBP1 promoter DNA methylation may become a key element in a panel of biomarkers for diagnosis, prevention, or therapy in SCZ and at risk individuals pending confirmatory studies with larger sample sizes to attain a higher degree of significance.

Subcortical structure alterations impact language processing in individuals with schizophrenia and those at high genetic risk

OBJECTIVE

Cortical structural and functional anomalies have been found to associate with language impairments in both schizophrenia patients and genetic high risk individuals for developing schizophrenia. However, subcortical structures that contribute to language processing haven't been well studied in this population, and thus became the main objective of this study.

METHOD

We examined structural MRI data from 20 patients with schizophrenia, 21 individuals at genetic high risk, and 48 controls. Surface shape and volume differences of 6 subcortical structures that are involved in language processing, including nuclei pallidum, putamen, caudate, amygdala, thalamus, and hippocampus from both hemispheres, were compared between groups. Performance scores of language-associated cognitive tests were obtained to identify relationships of subcortical structures to language-related behaviors.

RESULTS

Significantly reduced volumes of both the left and right side caudate nuclei, thalami and right side amygdala were shown in patients when compared with controls. Very interestingly, the high risk group demonstrated significantly increased correlations between volumes of left side pallidum nucleus and bilateral thalami and language-related cognitive test scores when compared to controls.

CONCLUSIONS

This study furthers our understanding of subcortical structural alterations in schizophrenia and high risk individuals, and suggests the contribution of subcortical structures to the language impairments that may serve as an early sign for impending development of schizophrenia.

Genetic association of GWAS-supported MAD1L1 gene polymorphism rs12666575 with schizophrenia susceptibility in a Chinese population

Schizophrenia (SCZ) is a severe neuropsychiatric disorder with high heritability. A recent European genome-wide association study has reported that mitotic arrest deficient-like 1 (MAD1L1) polymorphism rs12666575 is associated with SCZ susceptibility. This study aims to test the association of MAD1L1 variant rs12666575 with SCZ susceptibility in a Chinese population. A total of 1400 participants, which include 700 SCZ patients and 700 sex- and age-matched controls (Zhuang: 300, Han: 400, respectively), were genotyped using the Sequenom MassARRAY iPLEX platform. 591 SCZ patients underwent positive and negative syndrome scale (PANSS) assessment. Genetic association analysis was performed using the PLINK program. The results showed MAD1L1 rs12666575 polymorphism was significantly associated with SCZ susceptibility in the recessive model (p(adj)=0.013). Also, rs12666575 was significantly associated with general psychopathology sub-scale score (p(adj)=0.043) and thought disturbance factor score (p(adj)=0.045). Our data suggested that MAD1L1 rs12666575 polymorphism may play a protective role against SCZ in the Chinese population. Furthermore, rs12666575 may be associated with general psychopathology and thought disturbance in SCZ patients.

Animal models of gene-environment interaction in schizophrenia: A dimensional perspective

Schizophrenia has long been considered as a disorder with multifactorial origins. Recent discoveries have advanced our understanding of the genetic architecture of the disease. However, even with the increase of identified risk variants, heritability estimates suggest an important contribution of non-genetic factors. Various environmental risk factors have been proposed to play a role in the etiopathogenesis of schizophrenia. These include season of birth, maternal infections, obstetric complications, adverse events at early childhood, and drug abuse. Despite the progress in identification of genetic and environmental risk factors, we still have a limited understanding of the mechanisms whereby gene-environment interactions (G × E) operate in schizophrenia and psychoses at large. In this review we provide a critical analysis of current animal models of G × E relevant to psychotic disorders and propose that dimensional perspective will advance our understanding of the complex mechanisms of these disorders.