Epigenetic aberrations in leukocytes of patients with schizophrenia: association of global DNA methylation with antipsychotic drug treatment and disease onset

Epigenetic Regulation in Schizophrenia: Focus on Methylation and Histone Modifications in Human Studies

Despite extensive research over the last few decades, the etiology of schizophrenia (SZ) remains unclear. SZ is a pathological disorder that is highly debilitating and deeply affects the lifestyle and minds of those affected. Several factors (one or in combination) have been reported as contributors to SZ pathogenesis, including neurodevelopmental, environmental, genetic and epigenetic factors. Deoxyribonucleic acid (DNA) methylation and post-translational modification (PTM) of histone proteins are potentially contributing epigenetic processes involved in transcriptional activity, chromatin folding, cell division and apoptotic processes, and DNA damage and repair. After establishing a summary of epigenetic processes in the context of schizophrenia, this review aims to highlight the current understanding of the role of DNA methylation and histone PTMs in this disorder and their potential roles in schizophrenia pathophysiology and pathogenesis.

YBX1-Mediated DNA Methylation-Dependent SHANK3 Expression in PBMCs and Developing Cortical Interneurons in Schizophrenia

Schizophrenia (SCZ) is a severe psychiatric and neurodevelopmental disorder. The pathological process of SCZ starts early during development, way before the first onset of psychotic symptoms. DNA methylation plays an important role in regulating gene expression and dysregulated DNA methylation is involved in the pathogenesis of various diseases. The methylated DNA immunoprecipitation-chip (MeDIP-chip) is performed to investigate genome-wide DNA methylation dysregulation in peripheral blood mononuclear cells (PBMCs) of patients with first-episode SCZ (FES). Results show that the SHANK3 promoter is hypermethylated, and this hypermethylation (HyperM) is negatively correlated with the cortical surface area in the left inferior temporal cortex and positively correlated with the negative symptom subscores in FES. The transcription factor YBX1 is further found to bind to the HyperM region of SHANK3 promoter in induced pluripotent stem cells (iPSCs)-derived cortical interneurons (cINs) but not glutamatergic neurons. Furthermore, a direct and positive regulatory effect of YBX1 on the expression of SHANK3 is confirmed in cINs using shRNAs. In summary, the dysregulated SHANK3 expression in cINs suggests the potential role of DNA methylation in the neuropathological mechanism underlying SCZ. The results also suggest that HyperM of SHANK3 in PBMCs can serve as a potential peripheral biomarker of SCZ.

Are the epigenetic changes predictive of therapeutic efficacy for psychiatric disorders? A translational approach towards novel drug targets

The etiopathogenesis of mental disorders is not fully understood and accumulating evidence support that clinical symptomatology cannot be assigned to a single gene mutation, but it involves several genetic factors. More specifically, a tight association between genes and environmental risk factors, which could be mediated by epigenetic mechanisms, may play a role in the development of mental disorders. Several data suggest that epigenetic modifications such as DNA methylation, post-translational histone modification and interference of microRNA (miRNA) or long non-coding RNA (lncRNA) may modify the severity of the disease and the outcome of the therapy. Indeed, the study of these mechanisms may help to identify patients particularly vulnerable to mental disorders and may have potential utility as biomarkers to facilitate diagnosis and treatment of psychiatric disorders. This article summarizes the most relevant preclinical and human data showing how epigenetic modifications can be central to the therapeutic efficacy of antidepressant and/or antipsychotic agents, as possible predictor of drugs response.

DNA methylation levels of RELN promoter region in ultra-high risk, first episode and chronic schizophrenia cohorts of schizophrenia

The essential role of the Reelin gene (RELN) during brain development makes it a prominent candidate in human epigenetic studies of Schizophrenia. Previous literature has reported differing levels of DNA methylation (DNAm) in patients with psychosis. Therefore, this study aimed to (1) examine and compare RELN DNAm levels in subjects at different stages of psychosis cross-sectionally, (2) analyse the effect of antipsychotics (AP) on DNAm, and (3) evaluate the effectiveness and applicability of RELN promoter DNAm as a possible biological-based marker for symptom severity in psychosis.. The study cohort consisted of 56 healthy controls, 87 ultra-high risk (UHR) individuals, 26 first-episode (FE) psychosis individuals and 30 chronic schizophrenia (CS) individuals. The Positive and Negative Syndrome Scale (PANSS) was used to assess Schizophrenia severity. After pyrosequencing selected CpG sites of peripheral blood, the Average mean DNAm levels were compared amongst the 4 subgroups. Our results showed differing levels of DNAm, with UHR having the lowest (7.72 ± 0.19) while the CS had the highest levels (HC: 8.78 ± 0.35; FE: 7.75 ± 0.37; CS: 8.82 ± 0.48). Significantly higher Average mean DNAm levels were found in CS subjects on AP (9.12 ± 0.61) compared to UHR without medication (UHR(-)) (7.39 ± 0.18). A significant association was also observed between the Average mean DNAm of FE and PANSS Negative symptom factor (R² = 0.237, ß = -0.401, *p = 0.033). In conclusion, our findings suggested different levels of DNAm for subjects at different stages of psychosis. Those subjects that took AP have different DNAm levels. There were significant associations between FE DNAm and Negative PANSS scores. With more future experiments and on larger cohorts, there may be potential use of DNAm of the RELN gene as one of the genes for the biological-based marker for symptom severity in psychosis.

DNA Methylation Profiles of the DRD2 and NR3C1 Genes in Patients with Recent-Onset Psychosis

Objectives

Dopamine receptor D2 gene (DRD2) and glucocorticoid receptor gene (NR3C1) are implicated in the development of psychosis. We investigated methylation levels of DRD2 and NR3C1 in peripheral blood of patients with recent-onset (RO) psychosis using bisulfite pyrosequencing as well as its association with childhood trauma and rumination.

Methods

In all, 51 individuals with RO psychosis and 47 healthy controls were recruited. DNA methylation levels in the targeted regions of two genes were analyzed and compared. Childhood trauma and rumination were evaluated using the Early Trauma Inventory Self-Report Short Form (ETI-SF) and Brooding Scale (BS), respectively. Correlations between the scores of the ETI-SF and BS and methylation levels were explored.

Results

For DRD2, we found no significant differences between groups in terms of methylation level or association with childhood trauma or rumination. For NR3C1, we found a trend level significance for average value of all CpG sites and significant hypermethylation or hypomethylation at specific sites. There was also a significant positive correlation between the methylation level at the CpG8 site of NR3C1 exon 1F and negative symptom subscale score of the PANSS (PANSS-N).

Conclusion

Epigenetic alterations of NR3C1 are associated with the pathophysiology of psychosis. Further epigenetic studies will elucidate the molecular mechanisms underpinning the pathophysiology of psychosis.

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

BACKGROUND

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSION

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

Can epigenetics shine a light on the biological pathways underlying major mental disorders?

A significant proportion of the global burden of disease can be attributed to mental illness. Despite important advances in identifying risk factors for mental health conditions, the biological processing underlying causal pathways to disease onset remain poorly understood. This represents a limitation to implement effective prevention and the development of novel pharmacological treatments. Epigenetic mechanisms have emerged as mediators of environmental and genetic risk factors which might play a role in disease onset, including childhood adversity (CA) and cannabis use (CU). Particularly, human research exploring DNA methylation has provided new and promising insights into the role of biological pathways implicated in the aetio-pathogenesis of psychiatric conditions, including: monoaminergic (Serotonin and Dopamine), GABAergic, glutamatergic, neurogenesis, inflammatory and immune response and oxidative stress. While these epigenetic changes have been often studied as disease-specific, similarly to the investigation of environmental risk factors, they are often transdiagnostic. Therefore, we aim to review the existing literature on DNA methylation from human studies of psychiatric diseases (i) to identify epigenetic modifications mapping onto biological pathways either transdiagnostically or specifically related to psychiatric diseases such as Eating Disorders, Post-traumatic Stress Disorder, Bipolar and Psychotic Disorder, Depression, Autism Spectrum Disorder and Anxiety Disorder, and (ii) to investigate a convergence between some of these epigenetic modifications and the exposure to known risk factors for psychiatric disorders such as CA and CU, as well as to other epigenetic confounders in psychiatry research.

Quantitative detection of methylated SOCS-1 in schizophrenia and bipolar disorder considering SOCS-1 -1478CA/del polymorphism and clinical parameters

BACKGROUND

We aimed to investigate the quantitative detection of methylated suppressor of cytokine signaling-1 (SOCS-1) in schizophrenia (SCZ) and bipolar disorder (BD), considering SOCS-1 -1478CA/del polymorphism and clinical parameters.

METHODS

Our research is a case-control study in which 114 patients with SCZ, 86 patients with BD, and 80 volunteers as a healthy group participated. Bisulfite-converted DNA samples were analyzed using the real-time quantitative methylation-specific PCR (qMS-PCR) method to measure the methylation level of the SOCS-1 gene. In addition, SOCS-1 -1478CA/del gene polymorphism was analyzed with the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTS

When the SOCS-1 promoter methylation levels of SCZ and BD patients were compared with the control group, the methylation levels of SCZ and BD were significantly lower than the control group. An earlier age of illness onset was significantly related to the SOCS-1 promoter hypermethylation in DNA samples of SCZ patients. Again, SOCS-1 promoter hypermethylation was significantly associated with the higher Young Mania Rating Scale (YMRS) score in BD patients. While the SOCS-1 CA/CA genotype frequency was significantly higher in the control group than in the BD group, the del/del genotype was significantly related to a higher frequency of rapid cycling and a lower frequency of family history in the BD patient group.

CONCLUSION

In summary, the methylated SOCS-1 quantity in DNA samples of SCZ and BD patients were significantly lower than in control samples. Whereas the SOCS-1 -1478CA/del polymorphism was not related to SCZ, it may be associated with the BD.

Global DNA methylation changes in adults with attention deficit-hyperactivity disorder and its comorbidity with bipolar disorder: links with polygenic scores

Genetic and environmental factors contribute to the etiology of Attention Deficit-Hyperactivity Disorder (ADHD). In this sense, the study of epigenetic mechanisms could contribute to the understanding of the disorder's neurobiology. Global DNA methylation (GMe) evaluated through 5-methylcytosine levels could be a promising epigenetic biomarker to capture long-lasting biological effects in response to environmental and hormonal changes. We conducted the first assessment of GMe levels in subjects with ADHD (n = 394) and its main comorbidities in comparison to populational controls (n = 390). Furthermore, given the high genetic contribution to ADHD (heritability of 80%), polygenic risk scores (PRS) were calculated to verify the genetic contribution to GMe levels in ADHD and the comorbidities associated with GMe levels. The GMe levels observed in patients were lower than controls (P = 1.1e-8), with women being significantly less globally methylated than men (P = 0.002). Regarding comorbidities, the presence of bipolar disorder (BD) among patients with ADHD was associated with higher methylation levels compared to patients with ADHD without BD (P = 0.031). The results did not change when pharmacological treatment was accounted for in the analyses. The ADHD and BD most predictive PRSs were negatively (P = 0.0064) and positively (P = 0.0042) correlated with GMe, respectively. This study is the first to report an association between GMe, ADHD, and its comorbidity with BD and associations between PRSs for specific psychiatric disorders and GMe. Our findings add to previous evidence that GMe may be a relevant piece in the psychiatric disorders' etiological landscape.

Molecular phenotypes associated with antipsychotic drugs in the human caudate nucleus

Antipsychotic drugs are the current first-line of treatment for schizophrenia and other psychotic conditions. However, their molecular effects on the human brain are poorly studied, due to difficulty of tissue access and confounders associated with disease status. Here we examine differences in gene expression and DNA methylation associated with positive antipsychotic drug toxicology status in the human caudate nucleus. We find no genome-wide significant differences in DNA methylation, but abundant differences in gene expression. These gene expression differences are overall quite similar to gene expression differences between schizophrenia cases and controls. Interestingly, gene expression differences based on antipsychotic toxicology are different between brain regions, potentially due to affected cell type differences. We finally assess similarities with effects in a mouse model, which finds some overlapping effects but many differences as well. As a first look at the molecular effects of antipsychotics in the human brain, the lack of epigenetic effects is unexpected, possibly because long term treatment effects may be relatively stable for extended periods.

Present and future antipsychotic drugs: a systematic review of the putative mechanisms of action for efficacy and a critical appraisal under a translational perspective

Antipsychotics represent the mainstay of schizophrenia pharmacological therapy, and their role has been expanded in the last years to mood disorders treatment. Although introduced in 1952, many years of research were required before an accurate picture of how antipsychotics work began to emerge. Despite the well-recognized characterization of antipsychotics in typical and atypical based on their liability to induce motor adverse events, their main action at dopamine D2R to elicit the "anti-psychotic" effect, as well as the multimodal action at other classes of receptors, their effects on intracellular mechanisms starting with receptor occupancy is still not completely understood. Significant lines of evidence converge on the impact of these compounds on multiple molecular signaling pathways implicated in the regulation of early genes and growth factors, dendritic spine shape, brain inflammation, and immune response, tuning overall the function and architecture of the synapse. Here we present, based on PRISMA approach, a comprehensive and systematic review of the above mechanisms under a translational perspective to disentangle those intracellular actions and signaling that may underline clinically relevant effects and represent potential targets for further innovative strategies in antipsychotic therapy.

Glial changes in schizophrenia: Genetic and epigenetic approach

BACKGROUND

Schizophrenia (SCZ) is a severe mental illness that affects one percent of the population, affecting how people think, feel, and behave. Evidence suggests glial cell alteration and some researchers have found genetic risk loci and epigenetic marks that may regulate glia-related genes implicated in SCZ.

AIM

The aim of this study is to identify genetic and epigenetic changes that have been reported in glial cells or glial-associated genes in SCZ.

MATERIALS AND METHODS

We searched the articles from PubMed, PubMed Central, Medline, Medscape, and Embase databases up to December 2020 to identify relevant peer-reviewed articles in English. The titles and abstracts were screened to eliminate irrelevant citations.

RESULTS

Twenty-four original articles were included in the review. Studies were categorized into the following four thematic via: (1) oligodendrocytes, (2) microglia, (3) astrocytes, and (4) perspectives.

CONCLUSION

This study is the first of its kind to review research on genetic variants and epigenetic modifications associated with glia-related genes implicated in SCZ. Epigenetic evidence is considerably less than genetic evidence in this field. Understanding the pathways of some risk genes and their genetic and epigenetic regulation allows us to understand and find potential targets for future interventions in this mental illness.

Clozapine Long-Term Treatment Might Reduce Epigenetic Age Through Hypomethylation of Longevity Regulatory Pathways Genes

Long-term studies have shown significantly lower mortality rates in patients with continuous clozapine (CLZ) treatment than other antipsychotics. We aimed to evaluate epigenetic age and DNA methylome differences between CLZ-treated patients and those without psychopharmacological treatment. The DNA methylome was analyzed using the Infinium MethylationEPIC BeadChip in 31 CLZ-treated patients with psychotic disorders and 56 patients with psychiatric disorders naive to psychopharmacological treatment. Delta age (Δage) was calculated as the difference between predicted epigenetic age and chronological age. CLZ-treated patients were stratified by sex, age, and years of treatment. Differential methylation sites between both groups were determined using linear regression models. The Δage in CLZ-treated patients was on average lower compared with drug-naive patients for the three clocks analyzed; however, after data-stratification, this difference remained only in male patients. Additional differences were observed in Hannum and Horvath clocks when comparing chronological age and years of CLZ treatment. We identified 44,716 differentially methylated sites, of which 87.7% were hypomethylated in CLZ-treated patients, and enriched in the longevity pathway genes. Moreover, by protein-protein interaction, AMPK and insulin signaling pathways were found enriched. CLZ could promote a lower Δage in individuals with long-term treatment and modify the DNA methylome of the longevity-regulating pathways genes.

Comprehensive DNA Methylation Analysis of Human Neuroblastoma Cells Treated With Haloperidol and Risperidone

Accumulating evidence suggests that the epigenetic alterations induced by antipsychotics contribute to the therapeutic efficacy. However, global and site-specific epigenetic changes by antipsychotics and those shared by different classes of antipsychotics remain poorly understood. We conducted a comprehensive DNA methylation analysis of human neuroblastoma cells cultured with antipsychotics. The cells were cultured with low and high concentrations of haloperidol or risperidone for 8 days. DNA methylation assay was performed with the Illumina HumanMethylation450 BeadChip. We found that both haloperidol and risperidone tended to cause hypermethylation changes and showed similar DNA methylation changes closely related to neuronal functions. A total of 294 differentially methylated probes (DMPs), including 197 hypermethylated and 97 hypomethylated DMPs, were identified with both haloperidol and risperidone treatment. Gene ontology analysis of the hypermethylated probe-associated genes showed enrichment of genes related to the regulation of neurotransmitter receptor activity and lipoprotein lipase activity. Pathway analysis identified that among the DMP-associated genes, SHANK1 and SHANK2 were the major genes in the neuropsychiatric disorder-related pathways. Our data would be valuable for understanding the mechanisms of action of antipsychotics from an epigenetic viewpoint.

Head-to-head comparison of various antipsychotic agents on genome-wide methylation in schizophrenia

Aim: To explore possible differences in genome-wide methylation between schizophrenia patients who consume various antipsychotics. Methods: We compared DNA methylation in leukocytes between the following cohorts: clozapine (n = 19) versus risperidone (n = 19), clozapine (n = 12) versus olanzapine (n = 12), clozapine (n = 9) versus quetiapine (n = 9) and clozapine (n = 33) versus healthy controls (n = 33). Subjects were matched for age, sex, ethnicity, smoking status and leukocyte proportions. Results: No single CpG site reached genome-wide significance for clozapine versus risperidone/olanzapine/quetiapine. For clozapine versus quetiapine, one significantly differentially methylated region was found - ch5: 176797920-176798049 (fwer = 0.075). Clozapine versus healthy controls yielded thousands of significantly differentially methylated CpG sites. Conclusions: Establishing antipsychotic induced genome-wide methylation patterns will further elucidate the biological and clinical effects of antipsychotic administration.

Epigenetics of Schizophrenia

Schizophrenia (SCZ) is a chronic psychotic disorder that contributes significantly to disability, affecting behavior, thought, and cognition. It has long been known that there is a heritable component to schizophrenia; studies in both the pre-genomic and post-genomic era, however, have failed to elucidate fully the genetic basis for this complex disease. Epigenetic processes - broadly, those which contribute to changes in gene expression without altering the genetic code itself - may help to understand better the mechanisms leading to development of SCZ. The objective of this review is to synthesize current knowledge of the epigenetic mechanisms involved in schizophrenia. Specifically, DNA methylation studies in both peripheral and post-mortem brain samples in SCZ are reviewed, as are epigenetic mechanisms including histone modification. The promising role of non-coding RNA including micro-RNA (miRNA) and its role as a potential diagnostic and therapeutic biomarker is outlined, as are epigenetic age acceleration and telomere shortening. Finally, we discuss limitations in current knowledge and propose future research directions.

Subtypes of schizophrenia identified by multi-omic measures associated with dysregulated immune function

Epigenetic modifications are plausible molecular sources of phenotypic heterogeneity across schizophrenia patients. The current study investigated biological heterogeneity in schizophrenia using peripheral epigenetic profiles to delineate illness subtypes independent of their phenomenological manifestations. We applied epigenome-wide profiling with a DNA methylation array from blood samples of 63 schizophrenia patients and 59 healthy controls. Non-negative matrix factorization (NMF) and k-means clustering were performed to identify DNA methylation-related patient subtypes. The validity of the partition was tested by assessing the profile of the T cell receptor (TCR) repertoires. The uniqueness of the identified subtypes in relation to brain structural and clinical measures were evaluated. Two distinct patterns of DNA methylation profiles were identified in patients. One subtype (60.3% of patients) showed relatively limited changes in methylation levels and cell composition compared to controls, while a second subtype (39.7% of patients) exhibited widespread methylation level alterations among genes enriched in immune cell activity, as well as a higher proportion of neutrophils and lower proportion of lymphocytes. Differentiation of the two patient subtypes was validated by TCR repertoires, which paralleled the partition based on DNA methylation profiles. The subtype with widespread methylation modifications had higher symptom severity, performed worse on cognitive measures, and displayed greater reductions in fractional anisotropy of white matter tracts and evidence of gray matter thickening compared to the other subtype. Identification of a distinct subtype of schizophrenia with unique molecular, cerebral, and clinical features provide a novel parcellation of the schizophrenia syndrome with potential to guide development of individualized therapeutics.

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.

DNA methylation signature as a biomarker of major neuropsychiatric disorders

DNA methylation is a broadly-investigated epigenetic modification that has been considered as a heritable and reversible change. Previous findings have indicated that DNA methylation regulates gene expression in the central nervous system (CNS). Also, disturbance of DNA methylation patterns has been associated with destructive consequences that lead to human brain diseases such as neuropsychiatric disorders (NPDs). In this review, we comprehensively discuss the mechanism and function of DNA methylation and its most recent associations with the pathology of NPDs-including major depressive disorder (MDD), schizophrenia (SZ), autism spectrum disorder (ASD), bipolar disorder (BD), and attention/deficit hyperactivity disorder (ADHD). We also discuss how heterogeneous findings demand further investigations. Finally, based on the recent studies we conclude that DNA methylation status may have implications in clinical diagnostics and therapeutics as a potential epigenetic biomarker of NPDs.

Actualities in immunological markers and electrochemical sensors for determination of dopamine and its metabolites in psychotic disorders (Review)

Psychotic disorders represent a serious health concern. At this moment, anamnestic data, international criteria for diagnosis/classification from the Diagnostic and Statistical Manual of Mental Disorders-5 and the International Classification of Diseases-10 and diagnostic scales are used to establish a diagnosis. The most commonly used biomarkers in psychotic illnesses are those regarding the neuroimmune system, metabolic abnormalities, neurotrophins and neurotransmitter systems and proteomics. A current issue faced by clinicians is the lack of biomarkers to help develop a more accurate diagnosis, with the possibility of initiating the most effective treatment. The detection of biological markers for psychosis has the potential to contribute to improvements in its diagnosis, prognosis and treatment effectiveness. The mixture of multiple biomarkers may improve the ability to differentiate and classify these patients. In this sense, the aim of this study was to analyze the literature concerning the potential biomarkers that could be used in medical practice and to review the newest developments in electrochemical sensors used for dopamine detection, one of the most important exploited biomarkers.

Toward personalized medicine in schizophrenia: Genetics and epigenetics of antipsychotic treatment

Schizophrenia is a complex psychiatric disorder where genetic, epigenetic, and environmental factors play a role in disease onset, course of illness, and treatment outcome. Pharmaco(epi)genetic research presents an important opportunity to improve patient care through prediction of medication side effects and response. In this narrative review, we discuss the current state of research and important progress of both genetic and epigenetic factors involved in antipsychotic response, over the past five years. The review is largely focused on the following frequently prescribed antipsychotics: olanzapine, risperidone, aripiprazole, and clozapine. Several consistent pharmacogenetic findings have emerged, in particular pharmacokinetic genes (primarily cytochrome P450 enzymes) and pharmacodynamic genes involving dopamine, serotonin, and glutamate neurotransmission. In addition to studies analysing DNA sequence variants, there are also several pharmacoepigenetic studies of antipsychotic response that have focused on the measurement of DNA methylation. Although pharmacoepigenetics is still in its infancy, consideration of both genetic and epigenetic factors contributing to antipsychotic response and side effects no doubt will be increasingly important in personalized medicine. We provide recommendations for next steps in research and clinical evaluation.

Drug Response-Related DNA Methylation Changes in Schizophrenia, Bipolar Disorder, and Major Depressive Disorder

Pharmacotherapy is the most common treatment for schizophrenia (SCZ), bipolar disorder (BD), and major depressive disorder (MDD). Pharmacogenetic studies have achieved results with limited clinical utility. DNA methylation (DNAm), an epigenetic modification, has been proposed to be involved in both the pathology and drug treatment of these disorders. Emerging data indicates that DNAm could be used as a predictor of drug response for psychiatric disorders. In this study, we performed a systematic review to evaluate the reproducibility of published changes of drug response-related DNAm in SCZ, BD and MDD. A total of 37 publications were included. Since the studies involved patients of different treatment stages, we partitioned them into three groups based on their primary focuses: (1) medication-induced DNAm changes (n = 8); (2) the relationship between DNAm and clinical improvement (n = 24); and (3) comparison of DNAm status across different medications (n = 14). We found that only BDNF was consistent with the DNAm changes detected in four independent studies for MDD. It was positively correlated with clinical improvement in MDD. To develop better predictive DNAm factors for drug response, we also discussed future research strategies, including experimental, analytical procedures and statistical criteria. Our review shows promising possibilities for using BDNF DNAm as a predictor of antidepressant treatment response for MDD, while more pharmacoepigenetic studies are needed for treatments of various diseases. Future research should take advantage of a system-wide analysis with a strict and standard analytical procedure.

Methylome-wide association study of first-episode schizophrenia reveals a hypermethylated CpG site in the promoter region of the TNIK susceptibility gene

Accumulating evidence suggests that epigenetics plays an important role in the etiology of schizophrenia. Here, we performed a methylome-wide association study (MWAS) of first-onset schizophrenia patients and controls from the Han Chinese population using microarray technology. The DNA methylation profiles revealed 4494 differentially methylated CpG sites. Gene ontology (GO) analysis showed that the functions of differentially methylated genes were primarily involved in enzymatic activity, cytoskeleton organization and cell adhesion, and the TNIK (encoding TRAF2- and NCK-interacting kinase) gene was enriched in most of these terms. By combining the MWAS results with those of previous genome-wide association studies (GWASs), we identified 72 candidate genes located in 49 human genome loci. Among the overlapping genes, the most significantly methylated CpG sites were in the transcriptional start site (TSS) 200 region (cg21413905, P_unadjusted = 3.20 × 10^-5) of TNIK. TNIK was listed in the top 50 differentially methylated loci. The results of pyrosequencing and TNIK mRNA expression were consistent with those of the microarray study. Bioinformatics analyses, dual-luciferase reporter assays and chromatin immunoprecipitation (ChIP) studies showed that TNIK interacted with genes associated with schizophrenia and NRF1 was identified as a novel transcription factor (TF) that binds to TNIK in its TSS200 region. Thus, the regulatory function of NRF1 may be influenced by the status of the methylated CpG site in this region. In summary, our study provides new insights into the epigenetic mechanisms that regulate schizophrenia. Studies of the functions of TNIK methylation should be performed in vitro and in vivo to provide a better understanding of the pathophysiology of schizophrenia.

The neuroendocrine modulation of global DNA methylation in neuropsychiatric disorders

There is an increasing body of knowledge on the influence of differential DNA methylation of specific genomic regions in psychiatric disorders. However, fewer studies have addressed global DNA methylation (GMe) levels. GMe is an estimative of biological functioning that is regulated by pervasive mechanisms able to capture the big picture of metabolic and environmental influences upon gene expression. In the present perspective article, we highlighted evidence for the relationships between cortisol and sex hormones and GMe in psychiatric disorders. We argue that the far-reaching effects of cortisol and sexual hormones on GMe may lie on the pathways linking stress and mental health. Further research on these endocrine-epigenetic links may help to explain the role of environmental stress as well as sex differences in the prevalence of psychiatric disorders.

Early-Onset Schizophrenia: A Special Phenotype of the Disease Characterized by Increased MTHFR Polymorphisms and Aggravating Symptoms

BACKGROUND

Patients with early-onset schizophrenia usually exhibit more severe symptoms, revealing a potentially distinctive disease phenotype. Methylenetetrahydrofolate reductase (MTHFR) is a critical enzyme in folate conversion and methylation modification associated with the disease. We aimed to investigate the potential effects of MTHFR polymorphisms and related methylation patterns in patients with early-onset schizophrenia, which implies special phenotypes of schizophrenia.

METHODS

In 177 patients with schizophrenia, MTHFR polymorphism at three sites (C677T, A1298C, and G1793A) and the Positive and Negative Syndrome Scale (PANSS) were tested. Differential methylation positions (DMPs) and enrichment of genes and related pathways were analyzed by testing the genomic methylation level. Catechol-O-methyltransferase (COMT), solute carrier family 6 member 4 (SLC6A4), neuregulin1 (NRG1), and brain-derived neurotrophic factor (BDNF) were selected to evaluate the methylation levels of specific CpG regions by pyrosequencing.

RESULTS

Higher levels of symptom severity and MTHFR polymorphisms and lower levels of global DNA methylation in patients with early-onset schizophrenia were observed in this study. SLC6A4 was hypermethylated, and BDNF was hypomethylated in specific regions of patients with early-onset schizophrenia.

CONCLUSION

Aggravating symptoms, increased MTHFR polymorphisms, and reduced genomic methylation levels may be characteristics and underlying mechanisms of early-onset schizophrenia, which implies a special disease phenotype. Beyond that, specific genes and biological pathways may imply the potential phenotype of schizophrenia.

Epigenome-wide meta-analysis of blood DNA methylation and its association with subcortical volumes: findings from the ENIGMA Epigenetics Working Group

DNA methylation, which is modulated by both genetic factors and environmental exposures, may offer a unique opportunity to discover novel biomarkers of disease-related brain phenotypes, even when measured in other tissues than brain, such as blood. A few studies of small sample sizes have revealed associations between blood DNA methylation and neuropsychopathology, however, large-scale epigenome-wide association studies (EWAS) are needed to investigate the utility of DNA methylation profiling as a peripheral marker for the brain. Here, in an analysis of eleven international cohorts, totalling 3337 individuals, we report epigenome-wide meta-analyses of blood DNA methylation with volumes of the hippocampus, thalamus and nucleus accumbens (NAcc)-three subcortical regions selected for their associations with disease and heritability and volumetric variability. Analyses of individual CpGs revealed genome-wide significant associations with hippocampal volume at two loci. No significant associations were found for analyses of thalamus and nucleus accumbens volumes. Cluster-based analyses revealed additional differentially methylated regions (DMRs) associated with hippocampal volume. DNA methylation at these loci affected expression of proximal genes involved in learning and memory, stem cell maintenance and differentiation, fatty acid metabolism and type-2 diabetes. These DNA methylation marks, their interaction with genetic variants and their impact on gene expression offer new insights into the relationship between epigenetic variation and brain structure and may provide the basis for biomarker discovery in neurodegeneration and neuropsychiatric conditions.

Hypomethylation of SNCA in Idiopathic REM Sleep Behavior Disorder Associated With Phenoconversion

BACKGROUND

Hypomethylation of intron 1 of the α-synuclein (SNCA) gene has been extensively reported in the blood of patients with α-synucleinopathies. Idiopathic rapid eye movement sleep behavior disorder represents a prodromal stage of α-synucleinopathies. Methylation of α-synuclein intron 1 in idiopathic rapid eye movement sleep behavior disorder patients is largely unexplored. The objective of the current study was to assess blood α-synuclein intron 1 methylation in patients and to explore it as a potential biomarker to predict phenoconversion and monitor disease progression.

METHODS

Seventy-eight polysomnography-confirmed patients and 74 healthy controls were enrolled. After an average of 3.75 years of follow up, 16 patients converted to neurodegenerative diseases (converters), whereas 59 did not (nonconverters). Blood DNA was obtained at baseline from all participants, as well as at the follow-up visit for 27 patients. DNA methylation levels were determined using bisulfite pyrosequencing methods and were compared between patients and healthy controls, converters and nonconverters, and baseline and follow-up visits.

RESULTS

Hypomethylation at cytosine-phosphate-guanine 10, 11, 12, 13, and 17 was found in patients compared with healthy controls. Hypomethylation at cytosine-phosphate-guanine 17 was associated with an increased risk of clinical phenoconversion, which was further enhanced with the presence of subtle motor abnormalities. In addition, it appeared that later reduction in methylation levels at cytosine-phosphate-guanine 14, 15, and 16 was associated with disease progression.

CONCLUSIONS

Peripheral blood α-synuclein intron 1 was hypomethylated in idiopathic rapid eye movement sleep behavior disorder patients. α-Synuclein methylation levels may be useful biomarkers to screen patients, predict phenoconversion, and monitor disease progression. © 2020 International Parkinson and Movement Disorder Society.

Epigenetic Age Acceleration Was Delayed in Schizophrenia

Schizophrenia is a serious neuropsychiatric disorder with abnormal age-related neurodevelopmental (or neurodegenerative) trajectories. Although an accelerated aging hypothesis of schizophrenia has been proposed, the quantitative study of the disruption of the physiological trajectory caused by schizophrenia is inconclusive. In this study, we employed 3 "epigenetic clock" methods to quantify the epigenetic age of a large sample size of whole blood (1069 samples from patients with schizophrenia vs 1264 samples from unaffected controls) and brain tissues (500 samples from patients with schizophrenia vs 711 samples from unaffected controls). We observed significant positive correlations between epigenetic age and chronological age in both blood and brain tissues from unaffected controls and patients with schizophrenia, as estimated by 3 methods. Furthermore, we observed that epigenetic age acceleration was significantly delayed in schizophrenia from the whole blood samples (aged 20-90 years) and brain frontal cortex tissues (aged 20-39 years). Intriguingly, the genes regulated by the epigenetic clock also contained schizophrenia-associated genes, displaying differential expression and methylation in patients with schizophrenia and involving in the regulation of cell activation and development. These findings were further supported by the dysregulated leukocyte composition in patients with schizophrenia. Our study presents quantitative evidence for a neurodevelopmental model of schizophrenia from the perspective of a skewed "epigenetic clock." Moreover, landmark changes in an easily accessible biological sample, blood, reveal the value of these epigenetic clock genes as peripheral biomarkers for schizophrenia.

Epigenomic Dysregulation in Schizophrenia: In Search of Disease Etiology and Biomarkers

Schizophrenia is a severe psychiatric disorder with a complex array of signs and symptoms that causes very significant disability in young people. While schizophrenia has a strong genetic component, with heritability around 80%, there is also a very significant range of environmental exposures and stressors that have been implicated in disease development and neuropathology, such as maternal immune infection, obstetric complications, childhood trauma and cannabis exposure. It is postulated that epigenetic factors, as well as regulatory non-coding RNAs, mediate the effects of these environmental stressors. In this review, we explore the most well-known epigenetic marks, including DNA methylation and histone modification, along with emerging RNA mediators of epigenomic state, including miRNAs and lncRNAs, and discuss their collective potential for involvement in the pathophysiology of schizophrenia implicated through the postmortem analysis of brain tissue. Given that peripheral tissues, such as blood, saliva, and olfactory epithelium have the same genetic composition and are exposed to many of the same environmental exposures, we also examine some studies supporting the application of peripheral tissues for epigenomic biomarker discovery in schizophrenia. Finally, we provide some perspective on how these biomarkers may be utilized to capture a signature of past events that informs future treatment.

Epigenetic mechanisms in schizophrenia and other psychotic disorders: a systematic review of empirical human findings

Schizophrenia and other psychotic disorders are highly debilitating psychiatric conditions that lack a clear etiology and exhibit polygenic inheritance underlain by pleiotropic genes. The prevailing explanation points to the interplay between predisposing genes and environmental exposure. Accumulated evidence suggests that epigenetic regulation of the genome may mediate dynamic gene-environment interactions at the molecular level by modulating the expression of psychiatric phenotypes through transcription factors. This systematic review summarizes the current knowledge linking schizophrenia and other psychotic disorders to epigenetics, based on PubMed and Web of Science database searches conducted according to the PRISMA guidelines. Three groups of mechanisms in case-control studies  of human tissue (i.e., postmortem brain and bio-fluids) were considered: DNA methylation, histone modifications, and non-coding miRNAs. From the initial pool of 3,204 records, 152 studies met our inclusion criteria (11,815/11,528, 233/219, and 2,091/1,827 cases/controls for each group, respectively). Many of the findings revealed associations with epigenetic modulations of genes regulating neurotransmission, neurodevelopment, and immune function, as well as differential miRNA expression (e.g., upregulated miR-34a, miR-7, and miR-181b). Overall, actual evidence moderately supports an association between epigenetics and schizophrenia and other psychotic disorders. However, heterogeneous results and cross-tissue extrapolations call for future work. Integrating epigenetics into systems biology may critically enhance research on psychosis and thus our understanding of the disorder. This may have implications for psychiatry in risk stratification, early recognition, diagnostics, precision medicine, and other interventional approaches targeting epigenetic fingerprints.

Derivation of poly-methylomic profile scores for schizophrenia

Schizophrenia and bipolar disorder share biological features and environmental risk factors that may be associated with altered DNA methylation. In this study we sought to: 1) construct a novel 'Poly-Methylomic Profile Score (PMPS)' by transforming schizophrenia-associated epigenome-wide methylation from a previously published epigenome-wide association study (EWAS) into a single quantitative metric; and 2) examine associations between the PMPS and clinical status in an independent sample of 57 schizophrenia (SZ) cases, 59 bipolar disorder (BD) cases and 55 healthy controls (HC) for whom blood-derived DNA methylation was quantified using the Illumina 450 K methylation beadchip. We constructed five PMPSs at different p-value thresholds by summing methylation beta-values weighted by individual-CpG effect sizes from the meta-analysis of a previously published schizophrenia EWAS (comprising three separate cohorts with 675 [353 SZ and 322 HC] discovery cohort participants, 847 [414 SZ and 433 HC] replication cohort participants, and 96 monozygotic twin-pairs discordant for SZ). All SZ PMPSs were elevated in SZ participants relative to HCs, with the score calculated at a p-value threshold of 1 × 10^-5 accounting for the greatest amount of variance. All PMPSs were elevated in SZ relative to BD and none of the PMPSs were increased in BD, or in a combined cohort of BD and SZ cases, relative to HCs. PMPSs were also not associated with positive or negative symptom severity. That this SZ-derived PMPSs was elevated in SZ, but not BD, suggests that epigenome-wide methylation patterns may represent distinct pathophysiology that is yet to be elucidated.

Plasticity of DNA methylation, functional brain connectivity and efficiency in cognitive remediation for schizophrenia

Cognitive remediation (CR) is predicated on principles of neuroplasticity, but the actual molecular and neurocircuitry changes underlying cognitive change in individuals with impaired neuroplastic processes is poorly understood. The present study examined epigenetic-neurocircuitry-behavioral outcome measures in schizophrenia, before and after participating in a CR program that targeted higher-order cognitive functions. Outcome measures included DNA methylation of genes central to synaptic plasticity (CpG sites of Reelin promoter and BDNF promoter) from buccal swabs, resting-state functional brain connectivity and topological network efficiency, and global scores of a cognitive battery from 35 inpatients in a rehabilitative ward (18 CR, 17 non-CR) with similar premorbid IQ to 15 healthy controls. Baseline group differences between healthy controls and schizophrenia, group-by-time effects of CR in schizophrenia, and associations between the outcome measures were tested. Baseline functional connectivity abnormalities within the frontal, fronto-temporal and fronto-parietal regions, and trending decreases in global efficiency, but not DNA methylation, were found in schizophrenia; the frontal and fronto-temporal connectivity, and global efficiency correlated with global cognitive performance across all individuals. Notably, CR resulted in differential changes in Reelin promoter CpG methylation levels, altered within-frontal and fronto-temporal functional connectivity, increasing global efficiency and improving cognitive performance in schizophrenia, when compared to non-CR. In the CR inpatients, positive associations between the micro to macro measures: Reelin methylation changes, higher global efficiency and improving global cognitive performance were found. Present findings provide a neurobiological insight into potential CR-led epigenetics-neurocircuitry modifications driving cognitive plasticity.

Global DNA hypomethylation and its correlation to the betaine level in peripheral blood of patients with schizophrenia

Accumulating evidence suggests that aberrant epigenetic regulation is involved in the pathophysiology of major psychiatric disorders such as schizophrenia (SZ) and bipolar disorder (BD). We previously showed that the plasma level of betaine (N,N,N-trimethylglycine), a methyl-group donor, was significantly decreased in patients with first episode schizophrenia (FESZ). In this study, we identified decrease of global DNA methylation level in FESZ (N = 24 patients vs N = 42 controls), and found that global DNA methylation level was inversely correlated with scores on the global assessment of functioning (GAF) scale, and positively correlated with plasma betaine level. Notably, correlations between levels of betaine and its metabolites (N,N-dimethylglycine and sarcosine, N-methylglycine) were lower or lost in FESZ plasma, but remained high in controls. We further examined global DNA methylation levels in patients with chronic SZ (N = 388) and BD (N = 414) as well as controls (N = 430), and confirmed significant hypomethylation and decreased betaine level in SZ. We also found that patients with BD type I, but not those with BD type II, showed significant global hypomethylation. These results suggest that global hypomethylation associated with decreased betaine level in blood cells is common to SZ and BD, and may reflect common pathophysiology such as psychotic symptoms.

HTR1A, HTR1B, HTR2A, HTR2C and HTR6 Gene Polymorphisms and Extrapyramidal Side Effects in Haloperidol-Treated Patients with Schizophrenia

Schizophrenia is a serious, chronic psychiatric disorder requiring lifelong treatment. Extrapyramidal side effects (EPS) are common adverse reactions to antipsychotic medications. In addition to the dopaminergic system, serotonergic mechanisms, including serotonin (5-HT) receptors, might be involved in EPS development. This study aimed to examine molecular associations of HTR1A, HTR1B, HTR2A, HTR2C and HTR6 gene polymorphisms with acute EPS in 229 male schizophrenia patients, following two weeks of haloperidol monotherapy. The Simpson-Angus Rating Scale for Extrapyramidal Side Effects (SAS), Barnes Akathisia Rating Scale (BARS) and Extrapyramidal Symptom Rating Scale (ESRS) were used to evaluate EPS severity. Genotyping was performed using real-time PCR, following extraction of blood DNA. Significant acute EPS appeared in 48.03% of schizophrenia patients. For the rs13212041 HTR1B gene polymorphism, affecting microRNA regulation of HTR1B gene expression, a higher frequency of TT carriers was found among haloperidol-treated patients with akathisia when compared to the group without akathisia symptoms. In comparison to C-allele carriers, patients carrying the TT genotype had higher akathisia severity, as determined by the SAS, BARS and ESRS scales. These molecular findings suggest potential involvement of 5-HT_1B receptors in akathisia development following haloperidol treatment, as well as possible epigenetic mechanisms of serotonergic modulation associated with antipsychotic-induced EPS.

Catechol-O-methyltransferase gene promoter methylation as a peripheral biomarker in male schizophrenia

As an epigenetic modification, DNA methylation may reflect the interaction between genetic and environmental factors in the development of schizophrenia (SCZ). Catechol-O-methyltransferase (COMT) gene is a promising candidate gene of SCZ. In the present study, we investigate the association of COMT methylation with the risk of SCZ using bisulfite pyrosequencing technology. Significant association between DNA methylation of COMT and the risk of SCZ is identified (P = 1.618e−007). A breakdown analysis by gender shows that the significance is driven by males (P = 3.310e−009), but not by females. DNA methylation of COMT is not significantly associated with SCZ clinical phenotypes, including p300 and cysteine level. No interaction is found between COMT genotypes and the percent methylation of this gene. Receiver operating characteristic (ROC) curve shows that DNA methylation of COMT is able to predict the SCZ risk in males (area under curve [AUC] = 0.802, P = 1.91e−007). The current study indicates the clinical value of COMT methylation as a potential male-specific biomarker in SCZ diagnosis.

Antipsychotic Medications and DNA Methylation in Schizophrenia and Bipolar Disorder: A Systematic Review

The pharmacoepigenetics of antipsychotic treatment in severe mental illness is a growing area of research that aims to understand the interface between antipsychotic treatment and genetic regulation. Pharmacoepigenetics may some day assist in identifying treatment response mechanisms or become one of the components in the implementation of precision medicine. To understand the current evidence regarding the effects of antipsychotics on DNA methylation a systematic review with qualitative synthesis was performed through Pubmed, Embase and Psychinfo from earliest data to June 2019. Studies were included if they analyzed DNA methylation in an antipsychotic-treated population of patients with schizophrenia or bipolar disorder. Data extraction occurred via a standardized format and study quality was assessed. Twenty-nine studies were identified for inclusion. Study design, antipsychotic type, sample source, and methods of DNA methylation measurement varied across all studies. Eighteen studies analyzed methylation in patients with schizophrenia, four studies in patients with bipolar disorder, and seven studies in a combined sample of schizophrenia and bipolar disorder. Twenty-two studies used observational samples whereas the remainder used prospectively treated samples. Six studies assessed global methylation, five assessed epigenome-wide, and 15 performed a candidate epigenetic study. Two studies analyzed both global and gene-specific methylation, whereas one study performed a simultaneous epigenome-wide and gene-specific study. Only three genes were analyzed in more than one gene-specific study and the findings were discordant. The state of the pharmacoepigenetic literature on antipsychotic use is still in its early stages and uniform reporting of methylation site information is needed. Future work should concentrate on using prospective sampling with appropriate control groups and begin to replicate many of the novel associations that have been reported.

NMDA receptor hypofunction for schizophrenia revisited: Perspectives from epigenetic mechanisms

Schizophrenia (SZ) is a neurodevelopmental disorder with cognitive deficits manifesting during early stages of the disease. Evidence suggests that genetic factors in combination with environmental insults lead to complex changes to glutamatergic, GABAergic, and dopaminergic systems. In particular, the N-methyl-d-aspartate receptor (NMDAR), a major glutamate receptor subtype, is implicated in both the disease progression and symptoms of SZ. NMDARs are critical for synaptic plasticity and cortical maturation, as well as learning and memory processes. In fact, any deviation from normal NMDAR expression and function can have devastating consequences. Surprisingly, there is little evidence from human patients that direct mutations of NMDAR genes contribute to SZ. One intriguing hypothesis is that epigenetic changes, which could result from early insults, alter protein expression and contribute to the NMDAR hypofunction found in SZ. Epigenetics is referred to as modifications that alter gene transcription without changing the DNA sequence itself. In this review, we first discuss how epigenetic changes to NMDAR genes could contribute to NMDAR hypofunction. We then explore how NMDAR hypofunction may contribute to epigenetic changes in other proteins or genes that lead to synaptic dysfunction and symptoms in SZ. We argue that NMDAR hypofunction occurs in early stage of the disease, and it may consequentially initiate GABA and dopamine deficits. Therefore, targeting NMDAR dysfunction during the early stages would be a promising avenue for prevention and therapeutic intervention of cognitive and social deficits that remain untreatable. Finally, we discuss potential questions regarding the epigenetic of SZ and future directions for research.

Association of global DNA hypomethylation with post-operative cognitive dysfunction in elderly patients undergoing hip surgery

BACKGROUND

Post-operative cognitive dysfunction (POCD) is a decline of cognitive status that commonly occurs after surgery in elderly patients. Whether DNA methylation is associated with the development of POCD remains unclear.

METHODS

Subjects (N = 124) older than 65 years-of-age undergoing hip replacement surgery were enrolled. A battery of neuropsychiatric tests was used to examine the perioperative cognitive function of the patients. Early POCD was analyzed using the reliable change index (RCI), and subjects were diagnosed with POCD if RCI < -1.96. Peripheral leukocyte DNA was isolated, and DNA methylation was measured via 5-methylcytosine (mC) using Elisa.

RESULTS

Twenty-four patients (19.4%) developed early POCD. There was no difference in baseline 5-mC levels by POCD status. The 5-mC levels significantly decreased on day 7 after surgery in patients who developed early POCD (P = .004), but did not change in non-POCD patients. Moreover, post-operative 5-mC levels were significantly lower in POCD patients than those in non-POCD patients (P = .003). Bivariate logistic models adjusted for age, gender, BMI, duration of anesthesia, and education level clearly demonstrated an independent association between post-operative 5-mC level and early POCD.

CONCLUSIONS

Post-operative global hypomethylation of leukocyte DNA was associated with the development of early POCD.

TRIAL REGISTRATION

ClinicalTrial, NCT02965235. Registered 16 November 2016, https://www.clinicaltrials.gov/ct2/results?term=NCT02965235&rank=1#rowId0.

Psychotropic drug-induced genetic-epigenetic modulation of CRTC1 gene is associated with early weight gain in a prospective study of psychiatric patients

BACKGROUND

Metabolic side effects induced by psychotropic drugs represent a major health issue in psychiatry. CREB-regulated transcription coactivator 1 (CRTC1) gene plays a major role in the regulation of energy homeostasis and epigenetic mechanisms may explain its association with obesity features previously described in psychiatric patients. This prospective study included 78 patients receiving psychotropic drugs that induce metabolic disturbances, with weight and other metabolic parameters monitored regularly. Methylation levels in 76 CRTC1 probes were assessed before and after 1 month of psychotropic treatment in blood samples.

RESULTS

Significant methylation changes were observed in three CRTC1 CpG sites (i.e., cg07015183, cg12034943, and cg 17006757) in patients with early and important weight gain (i.e., equal or higher than 5% after 1 month; FDR p value = 0.02). Multivariable models showed that methylation decrease in cg12034943 was more important in patients with early weight gain (≥ 5%) than in those who did not gain weight (p = 0.01). Further analyses combining genetic and methylation data showed that cg12034943 was significantly associated with early weight gain in patients carrying the G allele of rs4808844A>G (p = 0.03), a SNP associated with this methylation site (p = 0.03).

CONCLUSIONS

These findings give new insights on psychotropic-induced weight gain and underline the need of future larger prospective epigenetic studies to better understand the complex pathways involved in psychotropic-induced metabolic side effects.

Sex-specific effects of methylenetetrahydrofolate reductase polymorphisms on schizophrenia with methylation changes

BACKGROUND

Methylenetetrahydrofolate reductase (MTHFR) is the critical enzyme in biotransformation. The polymorphism of MTHFR is a risk factor for schizophrenia. However, whether the MTHFR polymorphism is associated with schizophrenia disease phenotypes and what is the underlying mechanism of MTHFR polymorphism in schizophrenia is under-investigated. In this study, we aim to verify the correlation between MTHFR polymorphisms and clinical features of schizophrenia, while exploring the differential genomic methylation and disease related genes as the potential targets for schizophrenia.

METHOD

242 patients of schizophrenia and 234 matched healthy controls were enrolled in this study. Polymorphisms of MTHFR from three sites (C677T, A1298C, G1793A) were examined by Taqman fluorescence probe method in leukocytes from all subjects. The positive and negative syndrome scale (PANSS), trail making test (TMT) and Clinical Global Impression (CGI) were checked on patients. Genomic methylation was tested and analyzed in fields of differential methylation positions (DMPs) and enrichment of genes that are potentially related to schizophrenia.

RESULTS

Schizophrenic patients showed higher frequency of MTHFR polymorphisms at both single and multiple sites than healthy controls. Our data also showed that MTHFR C677T and multiple-site polymorphisms were positively correlated with PANSS positive rating, not negative score in male schizophrenia patients. Furthermore, while a significant reduction of global DNA methylation level was observed in schizophrenic patients, we also identified several genes which differentiated between schizophrenia and healthy controls at methylation levels.

CONCLUSIONS

This is a pilot study revealing that MTHFR polymorphisms at both single and multiple sites are related to the risk of schizophrenia and positive symptom of the disease. The risk of MTHFR polymorphism in schizophrenia and the clinical symptoms was only significant in male patients. While the sex-specific risk of MTHFR in schizophrenia is new and the reasons remain unanswered. Our methylation analysis suggested that there was significant hypomethylation of genomic DNA in schizophrenia patients with no sex difference. The correlation between MTHFR polymorphism and schizophrenia may attribute to the change of DNA methylation level, and some certain genes could be potential research objects for MTHFR effects on schizophrenia.

Association of MAD1L1 polymorphism (rs871925) with prenatal famine exposure and schizophrenia in a Chinese population: A case-control study

Schizophrenia (SCZ) is a complex, frequently disabling psychiatric disorder. Prenatal exposure to famine, an environmental factor, plays a significant role in the cause of SCZ. We used DNA methylation related sites to analyze their association with prenatal famine exposure and SCZ risk in a Northeast Han Chinese population. A total of 967 subjects (446 patients with SCZ/521 health controls) were recruited. Five single-nucleotide polymorphisms (rs2300149 in ITIH1, rs2675956 in NGEF, rs3758543 in NT5C2, rs7003288 in NA, and rs871925 in MAD1L1) were selected and genotyped. Genotype distribution and allele frequency analysis indicated that rs871925 was significantly associated with SCZ. We also found a significant association between prenatal exposure to famine and rs871925 in the recessive model in the health control group. The generalized multifactor dimensionality reduction analysis suggested a five-locus interaction model association with the risk of developing SCZ. Our data suggested that MAD1L1 rs871925 was associated with prenatal famine exposure and SCZ susceptibility in a Northeast Han Chinese population.

The Potential Role of Regulatory Genes (DNMT3A, HDAC5, and HDAC9) in Antipsychotic Treatment Response in South African Schizophrenia Patients

Despite advances in pharmacogenetics, the majority of heritability for treatment response cannot be explained by common variation, suggesting that factors such as epigenetics may play a key role. Regulatory genes, such as those involved in DNA methylation and transcriptional repression, are therefore excellent candidates for investigating antipsychotic treatment response. This study explored the differential expression of regulatory genes between patients with schizophrenia (chronic and antipsychotic-naïve first-episode patients) and healthy controls in order to identify candidate genes for association with antipsychotic treatment response. Seven candidate differentially expressed genes were identified, and four variants within these genes were found to be significantly associated with treatment response (DNMT3A rs2304429, HDAC5 rs11079983, and HDAC9 rs1178119 and rs11764843). Further analyses revealed that two of these variants (rs2304429 and rs11079983) are predicted to alter the expression of specific genes (DNMT3A, ASB16, and ASB16-AS1) in brain regions previously implicated in schizophrenia and treatment response. These results may aid in the development of biomarkers for antipsychotic treatment response, as well as novel drug targets.

Altered DNA methylation of the AluY subfamily in schizophrenia and bipolar disorder

Aim: To study DNA methylation patterns of AluY subfamilies in schizophrenia (SCZ) and bipolar disorder (BPD). Patients & methods: A bisulfite conversion-specific one-label extension method was employed to detect the AluY subfamily methylation levels of peripheral blood DNA from 92 SCZ patients, 99 BPD patients and 92 controls. Results: Hypermethylation of the AluY A1 and A2 CpG sites in BPD patients and hypomethylation of A3 CpG site in both of BPD and SCZ patients, and opposite age-dependent methylation alterations between SCZ and controls. Conclusion: The differentially altered DNA methylation patterns of the AluY families between BPD and SCZ suggest the role of DNA methylation in the pathogenesis of these major psychiatric disorders.

Placental epigenetics for evaluation of fetal congenital heart defects: Ventricular Septal Defect (VSD)

Ventricular Septal Defect (VSD), the most common congenital heart defect, is characterized by a hole in the septum between the right and left ventricles. The pathogenesis of VSD is unknown in most clinical cases. There is a paucity of data relevant to epigenetic changes in VSD. The placenta is a fetal tissue crucial in cardiac development and a potentially useful surrogate for evaluating the development of heart tissue. To understand epigenetic mechanisms that may play a role in the development of VSD, genome-wide DNA methylation assay on placentas of 8 term subjects with isolated VSD and no known or suspected genetic syndromes and 10 unaffected controls was performed using the Illumina HumanMethylation450 BeadChip assay. We identified a total of 80 highly accurate potential CpGs in 80 genes for detection of VSD; area under the receiver operating characteristic curve (AUC ROC) 1.0 with significant 95% CI (FDR) p-values < 0.05 for each individual locus. The biological processes and functions for many of these differentially methylated genes are previously known to be associated with heart development or disease, including cardiac ventricle development (HEY2, ISL1), heart looping (SRF), cardiac muscle cell differentiation (ACTC1, HEY2), cardiac septum development (ISL1), heart morphogenesis (SRF, HEY2, ISL1, HEYL), Notch signaling pathway (HEY2, HEYL), cardiac chamber development (ISL1), and cardiac muscle tissue development (ACTC1, ISL1). In addition, we identified 8 microRNAs that have the potential to be biomarkers for the detection of VSD including: miR-191, miR-548F1, miR-148A, miR-423, miR-92B, miR-611, miR-2110, and miR-548H4. To our knowledge this is the first report in which placental analysis has been used for determining the pathogenesis of and predicting VSD.

Enhanced Molecular Appreciation of Psychiatric Disorders Through High-Dimensionality Data Acquisition and Analytics

The initial diagnosis, molecular investigation, treatment, and posttreatment care of major psychiatric disorders (schizophrenia and bipolar depression) are all still significantly hindered by the current inability to define these disorders in an explicit molecular signaling manner. High-dimensionality data analytics, using large datastreams from transcriptomic, proteomic, or metabolomic investigations, will likely advance both the appreciation of the molecular nature of major psychiatric disorders and simultaneously enhance our ability to more efficiently diagnose and treat these debilitating conditions. High-dimensionality data analysis in psychiatric research has been heterogeneous in aims and methods and limited by insufficient sample sizes, poorly defined case definitions, methodological inhomogeneity, and confounding results. All of these issues combine to constrain the conclusions that can be extracted from them. Here, we discuss possibilities for overcoming methodological challenges through the implementation of transcriptomic, proteomic, or metabolomics signatures in psychiatric diagnosis and offer an outlook for future investigations. To fulfill the promise of intelligent high-dimensionality data-based differential diagnosis in mental disease diagnosis and treatment, future research will need large, well-defined cohorts in combination with state-of-the-art technologies.

Hypomethylation of LINE-1 elements in schizophrenia and bipolar disorder

Schizophrenia (SCZ) and bipolar disorder (BPD) are severe mental illnesses with evidence of significant genetic and environmental etiological elements in their complex etiologies. 5'-Methylcytosine is the main epigenetic DNA modification that mediates the interplay between genetic and environmental components. In humans, most 5'-methylcytosine modifications are observed in CpG-rich regions within the long interspersed nuclear element (LINE-1). LINE-1 is a mobile retrotransposon that comprises ∼17% of the human genome, and its methylation levels are highly correlated with global DNA methylation levels. LINE-1 insertions are also reported to be mental illnesses-associated genomic risk factors. To examine the LINE-1 methylation levels in SCZ and BPD, this study employed a bisulfite conversion-specific one-label extension (BS-OLE) method to detect the methylation levels at three CpG sites (S1, S2 and S3) of LINE-1 in peripheral blood DNA from a Han Chinese cohort composed of 92 SCZ patients, 99 BPD patients and 92 controls (CON). The results showed a decreased S1 methylation level in SCZ, decreased S2 methylation level in BPD and decreased S3 methylation levels in both SCZ and BPD relative to those of the CON. A female-dependent positive correlation of the S3 methylation level with age in CON became non-significant in both SCZ and BPD. These findings demonstrated that LINE-1 methylation varied with development and disease status. The roles of LINE-1 methylation in the pathogenesis of SCZ and BPD remain to be elucidated.

DNA Methylation as a Biomarker of Treatment Response Variability in Serious Mental Illnesses: A Systematic Review Focused on Bipolar Disorder, Schizophrenia, and Major Depressive Disorder

So far, genetic studies of treatment response in schizophrenia, bipolar disorder, and major depression have returned results with limited clinical utility. A gene × environment interplay has been proposed as a factor influencing not only pathophysiology but also the treatment response. Therefore, epigenetics has emerged as a major field of research to study the treatment of these three disorders. Among the epigenetic marks that can modify gene expression, DNA methylation is the best studied. We performed a systematic search (PubMed) following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA guidelines for preclinical and clinical studies focused on genome-wide and gene-specific DNA methylation in the context of schizophrenia, bipolar disorders, and major depressive disorder. Out of the 112 studies initially identified, we selected 31 studies among them, with an emphasis on responses to the gold standard treatments in each disorder. Modulations of DNA methylation levels at specific CpG sites have been documented for all classes of treatments (antipsychotics, mood stabilizers, and antidepressants). The heterogeneity of the models and methodologies used complicate the interpretation of results. Although few studies in each disorder have assessed the potential of DNA methylation as biomarkers of treatment response, data support this hypothesis for antipsychotics, mood stabilizers and antidepressants.

Impact of antipsychotic treatment on methylation status of Interleukin-6 [IL-6] gene in Schizophrenia

Immunopathogenesis of schizophrenia has emerged as one of the predominant research paradigms in recent times. Based on the altered serum levels as well as gene expression, IL-6 has been considered as a peripheral biomarker of schizophrenia. However, the precise mechanism underlying the altered expression of IL6 in schizophrenia is inadequately known. Given the profound influence of environmental factors on schizophrenia risk, it is important to understand the effect of epigenetic changes on schizophrenia risk. Further, it is not known whether epigenetic changes modulate the expression of IL6 and its subsequent effects on the risk and progression of schizophrenia. In this study, we analysed and compared the methylation status of IL6 promoter sequence from -1200bp to +27bp in antipsychotic-naïve/free schizophrenia patients (N = 47) and matched healthy controls (N = 47) using bisulfite sequencing method. In addition, we also examined the methylation status in these patients at least after 3-months of treatment with antipsychotics (N = 40). At baseline, a state of hypomethylation was observed in the IL6 promoter of schizophrenia subjects in comparison to healthy controls. This state of hypomethylation was shown to be reversed by the administration of antipsychotics. In summary, our observations emphasize a significant role for IL-6 promoter methylation in schizophrenia pathogenesis as well as treatment with antipsychotic medications.