The brain-derived neurotrophic factor gene in suicidal behaviour: a meta-analysis

Transcriptome profiling as a biological marker for bipolar disorder sub-phenotypes

PURPOSE

Bipolar affective disorder (BP) causes major functional impairment and reduced quality of life not only for patients, but also for many close relatives. We aimed to investigate mRNA levels in BP patients to find differentially expressed genes linked to specific clinical course variants; assuming that several gene expression alterations might indicate vulnerability pathways for specific course and severity of the disease.

MATERIALS

We searched for up- and down-regulated genes comparing patients with diagnosis of BP type I (BPI) vs type II (BPII), history of suicide attempts, psychotic symptoms, predominance of manic/hypomanic episodes, and history of numerous episodes and comorbidity of substance use disorders or anxiety disorders. RNA was extracted from peripheral blood mononuclear cells and analyzed with use of microarray slides.

RESULTS

Differentially expressed genes (DEGs) were found in all disease characteristics compared. The lowest number of DEGs were revealed when comparing BPI and BPII patients (18 genes), and the highest number when comparing patients with and without psychotic symptoms (3223 genes). Down-regulated genes identified here with the use of the DAVID database were among others linked to cell migration, defense response, and inflammatory response.

CONCLUSIONS

The most specific transcriptome profile was revealed in BP with psychotic symptoms. Differentially expressed genes in this variant include, among others, genes involved in inflammatory and immune processes. It might suggest the overlap of biological background between BP with a history of psychotic features and schizophrenia.

Genetic signatures of suicide attempt behavior: insights and applications

INTRODUCTION

Every year about 800,000 complete suicide events occur. The identification of biologic markers to identify subjects at risk would be helpful in targeting specific support treatments.

AREA COVERED

A narrative review defines the meta-analytic level of current evidence about the biologic markers of suicide behavior (SB). The meta-analytic evidence gathered so far indicates that the hypothesis-driven research largely failed to identify the biologic markers of suicide. The most consistent and replicated result was reported for: 1) 5-HTR2A T102C, associated with SB in patients with schizophrenia (OR = 1.73 (1.11-2.69)) and 2) BDNF Val66Met (rs6265), with the Met-Val + Val-Val carriers found to be at risk for suicide in the Caucasian population (OR: 1.96 (1.58-2.43)), while Val-Val vs. Val-Met + Met carriers found to be at risk for suicide in the Asian populations (OR: 1.36 (1.04-1.78)). GWAS-based meta-analyses indicate some positive replicated findings regarding the DRD2, Neuroligin gene, estrogen-related genes, and genes involved in gene expression.

EXPERT OPINION

Most consistent results were obtained when analyzing sub-samples of patients. Some promising results come from the implementation of the polygenic risk score. There is no current consensus about an implementable biomarker for SB.

Alterations of BDNF, mGluR5, Homer1a, p11 and excitatory/inhibitory balance in corticolimbic brain regions of suicide decedents

BACKGROUND

Developing biological based approaches for preventing suicide has become a priority. In recent years, there has been a surge in studies investigating the role of the glutamatergic system in suicide, although it remains unclear.

METHODS

We evaluated changes in the gene expression of the metabotropic glutamate receptor 5 (mGluR5) and its scaffolding proteins Homer1a and p11 in the dorsolateral prefrontal cortex (DLPFC), amygdala (AMY), and hippocampus (HIP) of 28 suicide decedents (S) (with no clinical psychiatric history or treatment with anxiolytics or antidepressants) and 26 controls (C) by real-time PCR (qPCR). Indeed, we measured BDNF gene expression and VGluT1 and VGAT immunoreactivities in the HIP by qPCR and immunohistochemistry, respectively. Cases and controls matched for age (C: 48.6 ± 11.6 years; S: 46.9 ± 14.5 years) and postmortem interval (PMI; C: 20.1 ± 13h; S: 16.9 ± 5h).

RESULTS

In DLPFC, S had lower p11 gene expression levels, but no differences were found in mGluR5 or Homer1a. In the AMY and HIP, mGluR5 and Homer1a were increased, p11 and BDNF were reduced. In the HIP, there were less VGAT-ir and more VGluT1-ir.

LIMITATIONS

Future studies are necessary to evaluate protein levels, and determine the cell types and potential compensatory mechanisms in a larger sample including S diagnosed with psychiatric disorders, females and different ethnicities.

CONCLUSIONS

This study identified significant alterations in mGluR5, Homer1a, p11, BDNF and excitatory/inhibitory balance in corticolimbic brain areas of S. These results further characterize the biological basis of suicide, contributing to the identification of potential biomarkers for suicide prevention.

Insights into the neurobiology of suicidality: explicating the role of glutamatergic systems through the lens of ketamine

Suicidality is a prevalent mental health condition, and managing suicidal patients is one of the most challenging tasks for health care professionals due to the lack of rapid-acting, effective psychopharmacological treatment options. According to the literature, suicide has neurobiological underpinnings that are not fully understood, and current treatments for suicidal tendencies have considerable limitations. To treat suicidality and prevent suicide, new treatments are required; to achieve this, the neurobiological processes underlying suicidal behavior must be thoroughly investigated. Although multiple neurotransmitter systems, particularly serotonergic systems, have been studied in the past, less has been reported in relation to disruptions in glutamatergic neurotransmission, neuronal plasticity, and neurogenesis that result from stress-related abnormalities of the hypothalamic-pituitary-adrenal system. Informed by the literature, which reports robust antisuicidal and antidepressive properties of subanaesthetic doses of ketamine, this review aims to provide an examination of the neurobiology of suicidality (and relevant mood disorders) with implications of pertinent animal, clinical, and postmortem studies. We discuss dysfunctions in the glutamatergic system, which may play a role in the neuropathology of suicidality and the role of ketamine in restoring synaptic connectivity at the molecular levels.

How to save a life: From neurobiological underpinnings to psychopharmacotherapies in the prevention of suicide

The impact of suicide on our societies, mental healthcare, and public health is beyond questionable. Every year approximately 700 000 lives are lost due to suicide around the world (WHO, 2021); more people die by suicide than by homicide and war. Although suicide is a key issue and reducing suicide mortality is a global imperative, suicide is a highly complex biopsychosocial phenomenon, and in spite of several suicidal models developed in recent years and a high number of suicide risk factors identified, we still have neither a sufficient understanding of underpinnings of suicide nor adequate management strategies to reduce its prevalence. The present paper first overviews the background of suicidal behavior including its epidemiology, prevalence, age and gender correlations and its association with neuropsychiatric disorders as well as its clinical assessment. Then we give an overview of the etiological background, including its biopsychosocial contexts, genetics and neurobiology. Based on the above, we then provide a critical overview of the currently available intervention options to manage and reduce risk of suicide, including psychotherapeutic modalities, traditional medication classes also providing an up-to-date overview on the antisuicidal effects of lithium, as well as novel molecules such as esketamine and emerging medications and further molecules in development. Finally we give a critical overview on our current knowledge on using neuromodulatory and biological therapies, such as ECT, rTMS, tDCS and other options.

Chronic running-wheel exercise from adolescence leads to increased anxiety and depression-like phenotypes in adulthood in rats: Effects on stress markers and interaction with BDNF Val66Met genotype

Exercise has been shown to be beneficial in reducing symptoms of affective disorders and to increase the expression of brain-derived neurotrophic factor (BDNF). The BDNF Val66Met polymorphism is associated with reduced activity-dependent BDNF release and increased risk for anxiety and depression. Male and female Val66Met rats were given access to running wheels from 3 weeks of age and compared to sedentary controls. Anxiety- and depression-like behaviors were measured in adulthood using the elevated plus maze (EPM), open field (OF), and forced swim test (FST). Expression of BDNF and a number of stress-related genes, the glucocorticoid receptor (Nr3c1), serum/glucocorticoid-regulated kinase 1 (Sgk1), and FK506 binding protein 51 (Fkbp5) in the hippocampus were also measured. Rats given access to running wheels developed high levels of voluntary exercise, decreased open-arm time on the EPM and center-field time in the OF, reduced overall exploratory activity in the open field, and increased immobility time in the FST with no differences between genotypes. Chronic exercise induced a significant increase in Bdnf mRNA and BDNF protein levels in the hippocampus with some of these effects being genotype specific. Exercise decreased the expression of Nr3c1 and Sgk1, but increased the expression of Fkbp5. These results suggest that chronic running-wheel exercise from adolescence increased anxiety and depression-like phenotypes in adulthood, independent of BDNF Val66Met genotype. Further studies are required to confirm that increased indices of anxiety-like behavior are independent from reduced overall locomotor activity.

Suicide and Neurotrophin Factors: A Systematic Review of the Correlation between BDNF and GDNF and Self-Killing

According to WHO data, suicide is a public health priority. In particular, suicide is the fourth-leading cause of death in young people. Many risk factors of suicide are described, including individual-, relationship-, community-, and societal-linked ones. The leading factor is the diagnosis of mental illness. Nevertheless, not all people who attempt suicide are psychiatric patients; these characteristics help define high-risk populations. There are currently no useful biomarkers to indicate the risk of suicide. In recent years, neurotrophic factors have increasingly become of scientific interest. This review aims to summarize the current scientific knowledge on the correlation between BDNF and GDNF and suicide, to theorize whether neurotrophins could be a reliable marker for an early diagnosis of suicidal risk. The authors conducted a systematic review following PRISMA criteria. They found eight research papers in agreement with the inclusion criteria. According to the results of these studies, there may be a connection between BDNF brain levels and complete suicide, although there are discrepancies. A lack of interest in GDNF may suggest less involvement in the suicidal dynamic. Further studies may provide helpful information to researchers.

Risk and Protective Factors for Childhood Physical Abuse and Suicidal Ideation: The Effect of Brain-Derived Neurotrophic Factor Polymorphism and Social Support

OBJECTIVE

This study aimed to explore the relationship between childhood physical abuse and suicidal ideation considering the effects of genetic and environmental factors in patients with post-traumatic stress disorder (PTSD) by focusing on brain-derived neurotrophic factor (BDNF) polymorphism and social support, respectively.

METHODS

One-hundred fourteen patients with PTSD and 94 healthy controls (HCs) were genotyped with respect to BDNF Val66Met polymorphism. All participants underwent psychological assessments. The hierarchical regression analysis and the simple slope analysis were conducted.

RESULTS

As for patients with PTSD, the moderation effect of BDNF polymorphism was significant but not for social support. Specifically, the BDNF Val/Val genotype worked as a risk factor and strengthens the relationship between childhood physical abuse and suicidal ideation. As for the HCs, the significant moderation effect was found only in social support, but not for BDNF polymorphism. The relationship between childhood physical abuse and suicidal ideation was weakened for the HCs with high social support.

CONCLUSION

This study demonstrated a significant BDNF genetic vulnerability for suicide in patients with PTSD who experienced childhood physical abuse. Our results suggested that social support provided a mitigating effect on the relationship between childhood physical abuse and suicidal ideation only in the HCs.

Behavioral phenotyping of a rat model of the BDNF Val66Met polymorphism reveals selective impairment of fear memory

The common brain-derived neurotrophic factor (BDNF) Val66Met polymorphism is associated with reduced activity-dependent BDNF release and increased risk for anxiety disorders and PTSD. Here we behaviorally phenotyped a novel Val66Met rat model with an equivalent valine to methionine substitution in the rat Bdnf gene (Val68Met). In a three-day fear conditioning protocol of fear learning and extinction, adult rats with the Met/Met genotype demonstrated impaired fear memory compared to Val/Met rats and Val/Val controls, with no genotype differences in fear learning or extinction. This deficit in fear memory occurred irrespective of the sex of the animals and was not seen in adolescence (4 weeks of age). There were no changes in open-field locomotor activity or anxiety measured in the elevated plus maze (EPM) nor in other types of memory measured using the novel-object recognition test or Y-maze. BDNF exon VI expression in the dorsal hippocampus was higher and BDNF protein level in the ventral hippocampus was lower in female Val/Met rats than female Val/Val rats, with no other genotype differences, including in total BDNF, BDNF long, or BDNF IV mRNA. These data suggest a specific role for the BDNF Met/Met genotype in fear memory in rats. Further studies are required to investigate gene-environment interactions in this novel animal model.

Peripheral BDNF levels in psychiatric patients with and without a history of suicide attempt: A systematic review and meta-analysis

OBJECTIVE

Psychiatric patients are at increased risk of attempting suicide. Several potential biomarkers of suicide risk have been proposed with inconsistent findings. The present paper aimed to evaluate differences in peripheral BDNF levels between psychiatric patients with and without a history of suicide attempts.

METHODS

We conducted a systematic review and meta-analysis following the PRISMA guidelines. Relevant papers published up to January 5, 2021 were identified searching the electronic databases Web of Knowledge^SM and PsycINFO. A random-effect meta-analysis was conducted using Stata 16.

RESULTS

Thirteen studies met inclusion criteria. Overall, no significant differences in BDNF levels between the two groups were found (13 studies, n = 1340, Hedge's g = -0.21, 95% CI -0.44 to 0.02). Heterogeneity was substantial (I² = 72.91%). Subgroup analyses revealed that BDNF levels were significantly reduced in plasma with medium effect size (5 studies, n = 363, Hedge's g = -0.44, 95% CI -0.86 to -0.02), but not in serum (8 studies, n = 977, Hedge's g = -0.09, 95% CI -0.33 to 0.15). No significant differences were found according to the type of diagnosis (major depressive disorder vs. other diagnoses) or the period of suicide attempt (lifetime vs. recent).

CONCLUSION

The utility of BDNF as a biomarker of suicide attempts in psychiatric patients appears limited to its plasma concentration. Although caution interpretation is needed, our findings may represent a starting point for the design of rigorous case-control studies exploring the association between neurotrophins and suicidal behaviors.

Advances in Research on Adolescent Suicide and a High Priority Agenda for Future Research

Suicide is the second leading cause of death for adolescents in the United States, yet remarkably little is known regarding risk factors for suicidal thoughts and behaviors (STBs), relatively few federal grants and scientific publications focus on STBs, and few evidence-based approaches to prevent or treat STBs are available. This "decade in review" article discusses five domains of recent empirical findings that span biological, environmental, and contextual systems and can guide future research in this high priority area: (1) the role of the central nervous system; (2) physiological risk factors, including the peripheral nervous system; (3) proximal acute stress responses; (4) novel behavioral and psychological risk factors; and (5) broader societal factors impacting diverse populations and several additional nascent areas worthy of further investigation.

Epigenetic studies in suicidal ideation and behavior

Most psychiatric disorders are associated with an elevated risk of suicide. Suicidal behavior is the product of the interaction of many risk factors, such as genetics and environmental factors. Hence, epigenetics research may help to understand the mechanisms leading to suicidal ideation and behavior. This review will discuss epigenetic studies in both suicidal ideation and behavior. Epigenetic modifications are likely to be important in both suicidal ideation and behavior. Most of the reviewed studies found significant epigenetic modifications linked with suicidal behavior rather than ideation. Although sizable research has been carried out on this topic, most studies have been done on small-scale samples, and future research is required in larger samples with better clinical characterization of suicide phenotypes to investigate these epigenetic modifications further.

Genome-wide association study of suicidal behaviour severity in mood disorders

OBJECTIVE

Suicide is a major public health problem and it has a prominent genetic component. We performed a genome-wide association study (GWAS) of suicidal behaviour severity.

METHODS

Suicide behaviour severity was assessed within the Schedules for Clinical Assessment in Neuropsychiatry in our mood disorder sample (n = 3506) for the GWAS. We also performed polygenic risk score analyses to explore genetic sharing between suicidal behaviour severity and a number of phenotypes, including bipolar disorder, major depressive disorder, alcoholism, post-traumatic stress disorder, impulsivity, insomnia, educational attainment, loneliness, maltreatment, and amygdala volume.

RESULTS

We did not detect genome-wide significant findings at the single-marker or gene level. We report a number of suggestive single-marker and gene-based findings. Our polygenic risk score analyses did not yield significant findings with these phenotypes.

CONCLUSIONS

Larger sample sizes are required to detect moderate effects.

SLC6A3 (DAT1) as a Novel Candidate Biomarker Gene for Suicidal Behavior

It has been previously shown that the serotonin and dopamine neurotransmitter systems might influence the predisposition to suicidal behavior. This study aims to estimate the contribution of 11 polymorphisms in the genes SLC6A4 (5HTT), HTR1A, HTR2A, HTR1B, SLC6A3 (DAT1), DRD4, DRD2, COMT, and BDNF to suicidal behavior and severity of symptoms of depression and anxiety in the Russian population. The study was performed on 100 patients with repeated suicide attempts and 154 controls. We first found an association between SLC6A3 (DAT1) 40 bp VNTR locus and suicidal behavior. This association was significant; when using the codominant (p = 0.006), dominant (p = 0.001), overdominant (p = 0.004), and log-additive (p = 0.004) models, LL genotype played a protective role (OR = 0.48, 0.29–0.82, p = 0.005). Difference in the distribution of COMT rs4680 genotypes was significant in the codominant (p = 0.04), dominant (p = 0.013), and log-additive (p = 0.02) models, and AA genotype might protect against suicide (OR = 0.49, 0.26–0.91, p = 0.025). SLC6A4 5-HTTLPR + rs25531 locus was significant in the recessive model (p = 0.024), and also affected the severity of symptoms of depression (p = 0.044) and personal anxiety (p = 0.029). Our results suggest that allelic variants of SLC6A3, COMT, and SLC6A4 genes might be considered as risk factors for suicidal attempts.

Modeling endophenotypes of suicidal behavior in animals

Suicide is a major public health concern. One of the common contributors to the increased risk for suicide is the genetic constitution of individuals, which determines certain endophenotypic traits used as quantifiable measure of neurobiological functions. Therefore, a logical deconstruction of the originating endophenotypes associated with suicidal risk could provide a better understanding of this complex disorder. In this regard, non-human animals can be a useful resource to test endophenotypes of suicidal behavior and the neurobiology underlying these endophenotypes. In this review, we have focused on the neurobiological abnormalities, primarily genetic and epigenetic abnormalities, associated with suicidal behavior and the scope of their modeling in animals. This can substantially advance the current understanding of suicidal behavior manifested with certain trait-based endophenotypes and may provide an opportunity to test novel hypotheses as well as aid in the development of treatment opportunities and risk assessment.

Brazilian Psychiatric Association guidelines for the management of suicidal behavior. Part 1. Risk factors, protective factors, and assessment

Suicide is a global public health problem that causes the loss of more than 800,000 lives each year, principally among young people. In Brazil, the average mortality rate attributable to suicide is approximately 5.23 per 100,000 population. Although many guidelines have been published for the management of suicidal behavior, to date, there are no recent guidelines based on the principles of evidence-based medicine that apply to the reality of suicide in Brazil. The objective of this work is to provide key guidelines for managing patients with suicidal behavior in Brazil. This project involved 11 Brazilian psychiatry professionals selected by the Psychiatric Emergencies Committee (Comissão de Emergências Psiquiátricas) of the Brazilian Psychiatric Association for their experience and knowledge in psychiatry and psychiatric emergencies. For the development of these guidelines, 79 articles were reviewed (from 5,362 initially collected and 755 abstracts). In this review, we present definitions, risk and protective factors, assessments, and an introduction to the Safety Plan.

Systematic review registry number: CRD42020206517

Suicide epigenetics, a review of recent progress

BACKGROUND

Suicide results in over 800,000 deaths every year, making it a major public health concern worldwide. It is highly complex, with genetic and environmental influences. Epigenetic mechanisms, including DNA methylation, miRNA, and histone modifications, could explain the complex interplay of environmental risk factors with genetic risk factors in the emergence of suicidal behavior.

METHODS

Here, we review the literature on suicide epigenetics over the past 10 years.

RESULTS

There has been significant progress in the field of suicide epigenetics, with emerging findings in the brain-derived neurotrophic factor and hypothalamic-pituitary-adrenal axis genes.

LIMITATIONS

Studying patient subgroups is needed in order to extract more comparable and reproducible epigenetic findings in suicide.

CONCLUSIONS

It is crucial to consider suicidal patients or suicide victims' distal and proximal past history e.g., early-life adversity and psychiatric disorder in epigenetic studies of suicidality.

Predicting risk of suicidal ideation in youth using a multigene panel for impulsive aggression

Childhood traumatic experiences and impulsive aggression are strong predictors of suicide ideation in youth.  This study examines whether a gene panel previously associated with impulsive aggression, together with a measure of traumatic experience, will predict suicidal ideation in youth. The sample consisted of 158 youth (ages 9-17 years) of European ancestry that participated in a case-control study for childhood aggression.  The Massachusetts Youth Screening Instrument (MAYSI-2) was used to examine suicide ideation and traumatic experiences. The impulsive aggression gene panel consists of 5 markers across 5 susceptibility genes (CRH, CRHR2, MC2R, OXTR, BDNF). A multi-gene risk score (MRS) for each individual was calculated by taking the total number of risk genotypes for that person. The covariates for the multiple regression model included sex, age, symptoms of anxiety/depression, MRS, traumatic experiences, and MRS x traumatic experience interaction. Results show the MRS x traumatic experience interaction term and the anxious/depressed symptoms to be significant predictors of suicide ideation in the full model. Importantly, genetic susceptibility to impulsive aggression and traumatic experiences remained a significant predictor for suicide ideation over and above the youth's level of anxiety and depression. This finding may have important implications for early intervention for youth suicide-related behaviors.

An examination of genes, stress and suicidal behavior in two First Nations communities: The role of the brain-derived neurotropic factor gene

Suicide claims over 800,000 lives each year worldwide. Suicide rates in indigenous populations in Canada are about double that of the national average, making it a serious public health issue. Numerous factors are involved in suicide risk, including genetic factors, as well as various psychosocial stressors, such as historical experience with the Indian Residential School system for Indigenous populations, as well as protective variables such as social support. Here, we report the first genetic study of suicidal behaviors that includes multiple measures of stress and social supports. We investigated the role of the functional Val66Met marker (rs6265) in the Brain-Derived Neurotropic Factor (BDNF) gene in suicidal ideation and suicide attempt in a First Nations community sample (N = 278). We did not find a significant association between the BDNF rs6265 marker and suicidal behaviors. We found childhood adversities, recent life stress, chronic stress, perceived stress, difficulties, and hazardous alcohol use to be associated with both suicidal ideation and suicide attempt. Thus, while additional studies with larger samples are required to elucidate the genetic component of suicide, addressing environmental stressors may be important for suicide prevention.

Circulating Levels of Brain-Derived Neurotrophic Factor and History of Suicide Attempts in Women

A growing body of research examining biological factors associated with suicidal behaviors highlights the role of brain-derived neurotropic factor (BDNF), involved in neurogenesis and synaptic plasticity. There is evidence suggesting that suicide attempters have lower BDNF levels than those with no history of suicide attempts. The key question addressed in the current investigation is whether differences in circulating BDNF levels persist beyond the current suicidal episode and would be observed in those with a past history of suicide attempts (SA). Plasma levels of BDNF were assessed in 73 women from the community. We found that women with a history of SA exhibited lower levels of BDNF than women with no SA history and this difference was maintained after statistically controlling for the influence of other potential psychiatric or demographic factors. These findings support and extend existing research by suggesting that circulating BDNF levels are decreased among individuals with a history of SA compared to individuals with no history of SA. This relation appeared to be specific to women's history of SA and was not explained by other potential psychiatric or demographic factors, which further highlights the role of BDNF as a promising biomarker for suicidal behavior.

Association between completed suicide and bipolar disorder: A systematic review of the literature

BACKGROUND

Completed suicide is a major cause of death in bipolar disorder (BD) patients.

OBJECTIVE

The aim of this paper is to provide an overall review of the existing literature of completed suicide in BD patients, including clinical and genetic data DATA SOURCES: We performed a systematic review of English and non-English articles published on MEDLINE/PubMed, PsycInfo and Cochrane database (1970-2017). Additional studies were identified by contacting clinical experts, searching bibliographies, major textbooks and website of World Health Organization. Initially we did a broad search for the association of bipolar disorder and suicide and we were narrowing the search in terms included "bipolar disorder" and "completed suicide".

STUDY SELECTION

Inclusion criteria were articles about completed suicide in patients with BD. Articles exclusively focusing on suicide attempts and suicidal behaviour have been excluded. We used PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) consensus for drafting this systematic review.

RESULTS

The initial search generated 2806 articles and a total of 61 meeting our inclusion criteria. We reviewed epidemiological data, genetic factors, risk factors and treatment of completed suicide in BD. Suicide rates in BD vary between studies but our analyses show that they are approximately 20-30-fold greater than in general population. The highest risk of successful suicide was observed in BD-II subjects. The heritability of completed suicide is about 40% and some genes related to major neurotransmitter systems have been associated with suicide. Lithium is the only treatment that has shown anti-suicide potential.

LIMITATIONS

The most important limitation of the present review is the limited existing literature on completed suicide in BD.

CONCLUSIONS

BD patients are at high risk for suicide. It is possible to identify some factors related to completed suicide, such as early onset, family history of suicide among first-degree relatives, previous attempted suicides, comorbidities and treatment. However it is necessary to promote research on this serious health problem.

Critical Issues in BDNF Val66Met Genetic Studies of Neuropsychiatric Disorders

Neurotrophins have been implicated in the pathophysiology of many neuropsychiatric diseases. Brain-derived neurotrophic factor (BDNF) is the most abundant and widely distributed neurotrophin in the brain. Its Val66Met polymorphism (refSNP Cluster Report: rs6265) is a common and functional single-nucleotide polymorphism (SNP) affecting the activity-dependent release of BDNF. BDNF Val66Met transgenic mice have been generated, which may provide further insight into the functional impact of this polymorphism in the brain. Considering the important role of BDNF in brain function, more than 1,100 genetic studies have investigated this polymorphism in the past 15 years. Although these studies have reported some encouraging positive findings initially, most of the findings cannot be replicated in following studies. These inconsistencies in BDNF Val66Met genetic studies may be attributed to many factors such as age, sex, environmental factors, ethnicity, genetic model used for analysis, and gene–gene interaction, which are discussed in this review. We also discuss the results of recent studies that have reported the novel functions of this polymorphism. Because many BDNF polymorphisms and non-genetic factors have been implicated in the complex traits of neuropsychiatric diseases, the conventional genetic association-based method is limited to address these complex interactions. Future studies should apply data mining and machine learning techniques to determine the genetic role of BDNF in neuropsychiatric diseases.

Sequence Analysis of Drug Target Genes with Suicidal Behavior in Bipolar Disorder Patients

Background

A number of genes have been implicated in recent genome-wide association studies of suicide attempt in bipolar disorder. More focused investigation of genes coding for protein targets of existing drugs may lead to drug repurposing for the treatment and/or prevention of suicide.

Methods

We analyzed 2,457 DNA variants across 197 genes of interest to GlaxoSmithKline across the pipeline in our sample of European patients suffering from bipolar disorder (N = 219). We analyzed these variants for a possible association with the suicide severity score (ranging from suicidal ideation/plan to serious suicide attempt) from the Schedule for Clinical Assessment in Neuropsychiatry. We conducted tests of individual variants and gene-based tests.

Results

We found a number of DNA variants in the transforming growth factor beta receptor 1 gene (TGFBR1) to be suggestively associated with suicide severity scores (p < 0.005). The gene-based tests also pointed to TGFBR1 to be associated with suicide severity (p = 0.0001). However, these findings were not replicated in an independent bipolar disorder sample.

Conclusions

We report no significant association between DNA sequences of drug target genes and suicidal behavior. Additional larger sequencing studies could further interrogate associations between variants in drug target genes and suicidal behavior.

The association between BDNF Val66Met polymorphism and emotional symptoms after mild traumatic brain injury

BACKGROUND

Brain-derived neurotrophic factor (BDNF) is one of the most abundant neurotrophins in the adult brain, and it plays important roles in modulating synaptic plasticity and synaptogenesis. This study attempted to elucidate the role of the BDNF variant rs6265 in emotional symptoms following mild traumatic brain injury (mTBI).

METHODS

To investigate the association between BDNF Val66Met polymorphism (rs6265) and emotional symptoms in mTBI patients, we recruited 192 mTBI patients and evaluated their Beck Anxiety Inventory (BAI) and Beck Depression Inventory (BDI) scores in the first and sixth week after mTBI.

RESULTS

The patients carrying the T allele of rs6265 had significantly higher BAI scores in the first week following mTBI. In addition, the patients carrying the T allele also showed higher scores of BDI in the first week. In the gender-specific subgroup analysis, the male patients carrying the T allele of rs6265 had higher scores of both BAI and BDI in the first and sixth week. Meanwhile, female patients carrying the T allele also had significantly higher scores of BDI in the first week following mTBI.

CONCLUSIONS

This study provides evidence for the association between the BDNF variant rs6265 and emotional symptoms following mTBI.

Genetic polymorphisms associated with smoking behaviour predict the risk of surgery in patients with Crohn's disease

BACKGROUND

Smoking is a strong environmental factor leading to adverse outcomes in Crohn's disease, but a more benign course in ulcerative colitis. Several single nucleotide polymorphisms (SNPs) are associated with smoking quantity and behaviour.

AIM

To assess whether smoking-associated SNPs interact with smoking to influence the clinical course of inflammatory bowel diseases.

METHODS

Genetic and prospectively obtained clinical data from 1434 Swiss inflammatory bowel disease cohort patients (821 Crohn's disease and 613 ulcerative colitis) were analysed. Six SNPs associated with smoking quantity and behaviour (rs588765, rs1051730, rs1329650, rs4105144, rs6474412 and rs3733829) were combined to form a risk score (range: 0-12) by adding the number of risk alleles. We calculated multivariate models for smoking, risk of surgery, fistula, Crohn's disease location and ulcerative colitis disease extent.

RESULTS

In Crohn's disease patients who smoke, the number of surgeries was associated with the genetic risk score. This translates to a predicted 3.5-fold (95% confidence interval: 2.4- to 5.7-fold, P<.0001) higher number of surgical procedures in smokers with 12 risk alleles than individuals with the lowest risk. Patients with a risk score >7 had a significantly shorter time to first intestinal surgery. The genetic risk score did not predict surgery in ulcerative colitis or occurrence of fistulae in Crohn's disease. SNP rs6265 was associated with ileal disease in Crohn's disease (P<.05) and proctitis in ulcerative colitis (P<.05).

CONCLUSIONS

SNPs associated with smoking quantity is associated with an increased risk for surgery in Crohn's disease patients who smoke. Our data provide an example of genetics interacting with the environment to influence the disease course of inflammatory bowel disease.

Antisuicidal Response Following Ketamine Infusion Is Associated With Decreased Nighttime Wakefulness in Major Depressive Disorder and Bipolar Disorder

OBJECTIVE

Insomnia and disrupted sleep are associated with increased risk of suicide. The N-methyl-d-aspartate antagonist ketamine has been associated with reduced suicidal thoughts, but the mechanism of action is unknown. This study sought to evaluate differences in nocturnal wakefulness in depressed individuals who did and did not have an antisuicidal response to ketamine.

METHODS

Thirty-four participants with baseline suicidal ideation diagnosed with either DSM-IV major depressive disorder (n = 23) or bipolar depression (n = 11) between 2006 and 2013 completed nighttime electroencephalography (EEG) the night before and the night after a single ketamine infusion (0.5 mg/kg over 40 minutes). Suicidal ideation was assessed at baseline and the morning after ketamine infusion via several measures, including the Hamilton Depression Rating Scale suicide item, the suicide item of the Montgomery-Asberg Depression Rating Scale, and the first 5 items of the Scale for Suicide Ideation. A generalized linear mixed model evaluated differences in nocturnal wakefulness, as verified by EEG, between those who had an antisuicidal response to ketamine and those who did not, controlling for baseline nocturnal wakefulness. Results were also compared to the sleep of healthy controls (n = 22).

RESULTS

After analyses adjusted for baseline sleep, participants with an antisuicidal response to ketamine showed significantly reduced nocturnal wakefulness the night after ketamine infusion compared to those without an antisuicidal response (F₁,₂₂ = 5.04, P = .04). Level of nocturnal wakefulness after antisuicidal response to ketamine did not differ significantly from nocturnal wakefulness in the control sample but did differ at a trend level (F₁,₄₀ = 3.15, P = .08).

CONCLUSIONS

Reductions in wakefulness following ketamine may point to a biological mechanism underlying the effect of ketamine on suicidal ideation.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00088699.

Exploring the association between BDNF Val66Met polymorphism and suicidal behavior: Meta-analysis and systematic review

Suicide is a serious worldwide health problem of critical consequences. Nowadays genetic factors are considered to be an important cause of suicide. The association between Val66Met (rs6265) polymorphism of the BDNF gene and suicide behavior has been increasingly studied. The aim of this study was to perform a meta-analysis in order to unravel the possible association between BDNF gene Val66Met polymorphism and suicide behavior. These meta-analysis and systematic review were performed using 23 articles that searched for a genetic association between Val66Met and suicide behavior, including 4532 cases and 5364 control subjects. The association was analyzed following the models: allelic, homozygous, heterozygous, dominant and recessive. Also, analyses by ethnicity (Caucasian and Asian populations) were done following the same four models. When the overall population was evaluated, we found no evidence of association between the polymorphism Val66Met of BDNF (rs6265) and suicide behavior (Met vs. Val: OR: 1.01; 95% CI = 0.92-1.10). However, a significant increased risk was found in the subgroup analysis by ethnicity in Caucasian populations (Met-Met vs. Met-Val + Val-Val: OR: 1.96; 95% CI = 1.58-2.43) and Asian populations (Val-Val vs. Val-Met + Met: OR: 1.36; 95% CI = 1.04-1.78). Our results suggest there is no association between the BDNF gene Val66Met (rs6265) and suicide behavior in the overall population. However, ethnic differences can be observed and the BDNF Val66Met might increase the risk for suicide behavior in Asian and Caucasian populations. Further studies with larger samples are necessary in order to have conclusive outcomes.

The Impact of BDNF Polymorphisms on Suicidality in Treatment-Resistant Major Depressive Disorder: A European Multicenter Study

BACKGROUND

Numerous studies have reported associations between the brain-derived neurotrophic factor (BDNF) gene and psychiatric disorders, including suicidal behavior, although with conflicting results.

METHODS

A total of 250 major depressive disorder patients were collected in the context of a European multicenter resistant depression study and treated with antidepressants at adequate doses for at least 4 weeks. Suicidality was assessed using the Mini International Neuropsychiatric Interview and Hamilton Rating Scale for Depression, and treatment response using the HAM-D. Genotyping was performed for the functional Val66Met polymorphism (rs6265) and 7 additional tagging single nucleotide polymorphisms within the BDNF gene.

RESULTS

Neither BDNF single markers nor haplotypes were found to be associated with suicide risk and lifetime history of suicide attempts. Gender-specific analyses revealed nonsignificant single marker (rs908867) and haplotypic association with suicide risk in males after multiple testing correction. Analyzing treatment response phenotypes, the functional Val66Met polymorphism as well as rs10501087 showed significant genotypic and haplotypic association with suicide risk in remitters (n=34, 13.6%).

CONCLUSIONS

Considering the sample size, the present findings need to be replicated in larger samples to confirm or refute a role of BDNF in the investigated suicidal behavior phenotypes.

Therapeutic Potentials of BDNF/TrkB in Breast Cancer; Current Status and Perspectives

Brain-derived neurotrophic factor (BDNF) is a potent neurotrophic factor that has been shown to stimulate breast cancer cell growth and metastasis via tyrosine kinase receptors TrkA, TrkB, and the p75^NTR death receptor. The aberrant activation of BDNF/TrkB pathways can modulate several signaling pathways, including Akt/PI3K, Jak/STAT, NF-kB, UPAR/UPA, Wnt/β-catenin, and VEGF pathways as well as the ER receptor. Several microRNAs have been identified that are involved in the modulation of BDNF/TrkB pathways. These include miR-206, miR-204, MiR-200a/c, MiR-210, MiR-134, and MiR-191; and these may be of value as prognostic and predictive biomarkers for detecting patients at high risk of developing breast cancer. It has been also been demonstrated that a high expression of genes involved in the BDNF pathway in breast cancer is associated with poor clinical outcome and reduced survival of patients. Several approaches have been developed for targeting this pathway, for example TKr inhibitors (AZD6918, CEP-701) and RNA interference. The aim of the current review was to provide an overview of the role of BDNF/TrkB pathways in the pathogenesis of breast cancer and its value as a potential therapeutic target. J. Cell. Biochem. 118: 2502-2515, 2017. © 2017 Wiley Periodicals, Inc.

Understanding Suicide Risk within the Research Domain Criteria (RDoC) Framework: Insights, Challenges, and Future Research Considerations

Suicide is a leading cause of death worldwide. Prior research has focused primarily on sociodemographic and psychiatric risk factors with little improvement in the prediction or prevention of suicidal behavior over time. The Research Domain Criteria (RDoC) may be an especially useful framework for advancing research in this area. This paper provides a brief and broad overview of research on suicidal behavior relating to each of the RDoC domains-highlighting the RDoC construct(s) where research has focused, construct(s) where research is lacking, and suggestions for future research directions. We also discuss major challenges for suicide research within the RDoC framework, including the intersection of RDoC domains, interaction of domains with the environment, incorporation of developmental stage, integration of distal and proximal processes, and inclusion of suicide-specific constructs. We conclude by underscoring important considerations for future research aimed at using the RDoC framework to study suicidal behavior and other forms of psychopathology.

The Life Span Model of Suicide and Its Neurobiological Foundation

The very incomprehensibility of the suicidal act has been occupying the minds of researchers and health professionals for a long time. Several theories of suicide have been proposed since the beginning of the past century, and a myriad of neurobiological studies have been conducted over the past two decades in order to elucidate its pathophysiology. Both neurobiology and psychological theories tend to work in parallel lines that need behavioral and empirical data respectively, to confirm their hypotheses. In this review, we are proposing a "Life Span Model of Suicide" with an attempt to integrate the "Stress-Diathesis Model" and the "Interpersonal Model of Suicide" into a neurobiological narrative and support it by providing a thorough compilation of related genetic, epigenetic, and gene expression findings. This proposed model comprises three layers, forming the capability of suicide: genetic factors as the predisposing Diathesis on one side and Stress, characterized by epigenetic marks on the other side, and in between gene expression and gene function which are thought to be influenced by Diathesis and Stress components. The empirical evidence of this model is yet to be confirmed and further research, specifically epigenetic studies in particular, are needed to support the presence of a life-long, evolving capability of suicide and identify its neurobiological correlates.

Association of Brain-Derived Neurotrophic Factor G196A and Attempted Suicide: A Case-Control Study in Rural China

BACKGROUND

Suicide is an important public problem, the mechanism of which has not been clarified. Many studies have focused on the molecular, biological and genetic mechanisms of suicide. Brain-derived neurotrophic factor (BDNF) G196A is one of the most leading loci in recent studies, but the results are inconsistent.

METHODS

We conducted a 1:1 age- and sex-matched case-control study in rural areas of Shandong Province, China. A total of 365 pairs of cases and controls were finally recruited into our study. The adjusted odds ratios (AORs) of BDNF 196G/G and their 95% confidence intervals (CIs) were calculated by multivariate conditional logistic regression models.

RESULTS

No association between BDNF polymorphisms and attempted suicide was found in the overall population. However, the BDNF 196G/G genotype was significantly related to attempted suicide in the elderly population (AOR = 7.85, 95% CI: 1.12-54.90, p = 0.038), while the associations were not significant in young and middle-aged groups.

CONCLUSION

Our study suggests that the BDNF 196G/G genotype increases the risk of attempted suicide in elderly people.

Clinical and genetic factors associated with suicide in mood disorder patients

Suicidality is a continuum ranging from ideation to attempted and completed suicide, with a complex etiology involving both genetic heritability and environmental factors. The majority of suicide events occur in the context of psychiatric conditions, preeminently major depression and bipolar disorder. The present study investigates clinical factors associated with suicide in a sample of 553 mood disorder patients, recruited within the 'Psy Pluriel' center, Centre Européen de Psychologie Médicale, and the Department of Psychiatry of Erasme Hospital (Brussels). Furthermore, genetic association analyses examining polymorphisms within COMT, BDNF, MAPK1 and CREB1 genes were performed in a subsample of 259 bipolar patients. The presence or absence of a previous suicide attempt and of current suicide risk were assessed. A positive association with suicide attempt was reported for younger patients, females, lower educated, smokers, those with higher scores on depressive symptoms and higher functional disability and those with anxiety comorbidity and familial history of suicidality in first- and second-degree relatives. Anxiety disorder comorbidity was the stronger predictor of current suicide risk. No associations were found with polymorphisms within COMT and BDNF genes, whereas significant associations were found with variations in rs13515 (MAPK1) and rs6740584 (CREB1) polymorphisms. From a clinical perspective, our study proposes several clinical characteristics, such as increased depressive symptomatology, anxiety comorbidity, functional disability and family history of suicidality, as correlates associated with suicide. Genetic risk variants in MAPK1 and CREB1 genes might be involved in a dysregulation of inflammatory and neuroplasticity pathways and are worthy of future investigation.

Genetic Association Studies of Suicidal Behavior: A Review of the Past 10 Years, Progress, Limitations, and Future Directions

Suicidal behaviors (SBs), which range from suicidal ideation to suicide attempts and completed suicide, represent a fatal dimension of mental ill-health. The involvement of genetic risk factors in SB is supported by family, twin, and adoption studies. The aim of this paper is to review recent genetic association studies in SBs including (i) case-control studies, (ii) family-based association studies, and (iii) genome-wide association studies (GWAS). Various studies on genetic associations have tended to suggest that a number of genes [e.g., tryptophan hydroxylase, serotonin receptors and transporters, or brain-derived neurotrophic factors (BDNFs)] are linked to SBs, but these findings are not consistently supported by the results obtained. Although the candidate-gene approach is useful, it is hampered by the present state of knowledge concerning the pathophysiology of diseases. Interpretations of GWAS results are mostly hindered by a lack of annotation describing the functions of most variation throughout the genome. Association studies have addressed a wide range of single-nucleotide polymorphisms in numerous genes. We have included 104 such studies, of which 10 are family-based association studies and 11 are GWAS. Numerous meta-analyses of case-control studies have shown significant associations of SB with variants in the serotonin transporter gene (5-HTT or SLC6A4) and the tryptophan hydroxylase 1 gene (TPH1), but others report contradictory results. The gene encoding BDNF and its receptor (NTRK2) are also promising candidates. Only two of the GWAS showed any significant associations. Several pathways are mentioned in an attempt to understand the lack of reproducibility and the disappointing results. Consequently, we review and discuss here the following aspects: (i) sample characteristics and confounding factors; (ii) statistical limits; (iii) gene-gene interactions; (iv) gene, environment, and by time interactions; and (v) technological and theoretical limits.

Genetic Vulnerability as a Distal Risk Factor for Suicidal Behaviour: Historical Perspective and Current Knowledge

INTRODUCTION

Suicide is a multidimensional problem. Observations of family history of suicide suggest the existence of a genetic vulnerability to suicidal behaviour.

AIM

Starting with a historical perspective, the article reviews current knowledge of a genetic vulnerability to suicidal behaviour, distinct from the genetic vulnerability to psychiatric disorders, focused on clinical and population-based studies, and findings from recent molecular genetics association studies.

METHOD

The review includes peer-reviewed research articles and review papers from the professional literature in English language, retrieved from PubMed/Medline and PsycINFO.

RESULTS

The research literature confirms a existence of a genetic vulnerability to suicidal behaviour. Even though the results of individual studies are difficult to compare, genetic influences could explain up to half of the variance of the occurrence of suicide.

CONCLUSION

Genetic vulnerability could be a distal risk factor for suicide, which helps us to understand the occurrence of suicide among vulnerable people. Ethical implications of such vulnerability are highlighted.

The BDNF gene Val66Met polymorphism as a modifier of psychiatric disorder susceptibility: progress and controversy

Brain-derived neurotrophic factor (BDNF) has a primary role in neuronal development, differentiation and plasticity in both the developing and adult brain. A single-nucleotide polymorphism in the proregion of BDNF, termed the Val66Met polymorphism, results in deficient subcellular translocation and activity-dependent secretion of BDNF, and has been associated with impaired neurocognitive function in healthy adults and in the incidence and clinical features of several psychiatric disorders. Research investigating the Val66Met polymorphism has increased markedly in the past decade, and a gap in integration exists between and within academic subfields interested in the effects of this variant. Here we comprehensively review the role and relevance of the Val66Met polymorphism in psychiatric disorders, with emphasis on suicidal behavior and anxiety, eating, mood and psychotic disorders. The cognitive and molecular neuroscience of the Val66Met polymorphism is also concisely reviewed to illustrate the effects of this genetic variant in healthy controls, and is complemented by a commentary on the behavioral neuroscience of BDNF and the Val66Met polymorphism where relevant to specific disorders. Lastly, a number of controversies and unresolved issues, including small effect sizes, sampling of allele inheritance but not genotype and putative ethnicity-specific effects of the Val66Met polymorphism, are also discussed to direct future research.

Gender and brain regions specific differences in brain derived neurotrophic factor protein levels of depressed individuals who died through suicide

Considerable evidence supports the view that depressive illness and suicidal behaviour stem from perturbations of neuroplasticity. Presently, we assessed whether depressed individuals who died by suicide displayed brain region-specific changes in brain derived neurotrophic factor (BDNF) and whether such effects varied by gender. Using postmortem samples from non-psychiatric controls and depressed individuals who died by suicide, BDNF protein levels were assessed within the hippocampus and frontopolar prefrontal cortex using Western blot. As expected, BDNF levels were reduced within the frontopolar prefrontal cortex among female depressed suicides; however, males showed no such effect. Contrastingly, within the hippocampus, depressed male but not female suicides displayed significant reductions of BDNF protein levels. Although the mechanisms driving the gender and brain region specific BDNF changes are unclear, our data do support the notion that complex alterations of neuroplasticity may be fundamentally involved in the illness.

An excitatory synapse hypothesis of depression

Depression is a common cause of mortality and morbidity, but the biological bases of the deficits in emotional and cognitive processing remain incompletely understood. Current antidepressant therapies are effective in only some patients and act slowly. Here, we propose an excitatory synapse hypothesis of depression in which chronic stress and genetic susceptibility cause changes in the strength of subsets of glutamatergic synapses at multiple locations, including the prefrontal cortex (PFC), hippocampus, and nucleus accumbens (NAc), leading to a dysfunction of corticomesolimbic reward circuitry that underlies many of the symptoms of depression. This hypothesis accounts for current depression treatments and suggests an updated framework for the development of better therapeutic compounds.

Investigation of the genetic interaction between BDNF and DRD3 genes in suicidical behaviour in psychiatric disorders

OBJECTIVES

Suicide is a serious public health concern, and it is partly genetic. The brain-derived neurotrophic factor (BDNF) gene has been a strong candidate in genetic studies of suicide (Dwivedi et al., Arch Gen Psychiatry 2010;60:804-815; Zai et al., Prog Neuropsychopharmacol Biol Psychiatry 2012;34:1412-1418) and BDNF regulates the expression of the dopamine D3 receptor.

OBJECTIVE

We examined the role of the BDNF and DRD3 genes in suicide.

METHODS

We analysed four tag single-nucleotide polymorphisms (SNPs) in BDNF and 15 SNPs in the D3 receptor gene DRD3 for possible association with suicide attempt history in our Canadian sample of Schizophrenia (SCZ) patients of European ancestry (N = 188).

RESULTS

In this sample, we found a possible interaction between the BDNF Val66Met and DRD3 Ser9Gly SNPs in increasing the risk of suicide attempt(s) in our SCZ sample. Specifically, a larger proportion of SCZ patients who were carrying at least one copy of the minor allele at each of the Val66Met and Ser9Gly functional markers have attempted suicides compared to patients with other genotypes (Bonferroni P < 0.05). However, we could not replicate this finding in samples from other psychiatric populations.

CONCLUSIONS

Taken together, the results from the present study suggest that an interaction between BDNF and DRD3 may not play a major role in the risk for suicide attempt, though further studies, especially in SCZ, are required.

An overview of the neurobiology of suicidal behaviors as one meta-system

Suicidal behaviors (SB) may be regarded as the outmost consequence of mental illnesses, or as a distinct entity per se. Regardless, the consequences of SB are very large to both society and affected individuals. The path leading to SB is clearly a complex one involving interactions between the subject's biology and environmental influences throughout life. With the aim to generate a representative and diversified overview of the different neurobiological components hypothesized or shown implicated across the entire SB field up to date by any approach, we selected and compiled a list of 212 gene symbols from the literature. An increasing number of novel gene (products) have been introduced as candidates, with half being implicated in SB in only the last 4 years. These candidates represent different neuro systems and functions and might therefore be regarded as competing or redundant explanations. We then adopted a unifying approach by treating them all as parts of the same meta-system, using bioinformatic tools. We present a network of all components connected by physical protein-protein interactions (the SB interactome). We proceeded by exploring the differences between the highly connected core (~30% of the candidate genes) and its peripheral parts, observing more functional homogeneity at the core, with multiple signal transduction pathways and actin-interacting proteins connecting a subset of receptors in nerve cell compartments as well as development/morphology phenotypes and the stress-sensitive synaptic plasticity processes of long term potentiation/depression. We suggest that SB neurobiology might also be viewed as one meta-system and perhaps be explained as intrinsic unbalances acting within the core or as imbalances arising between core and specific peripheral components.

Epigenetic studies of suicidal behavior

Recent studies have shown an association between gene alterations by epigenetic mechanisms and suicidal behavior. These epigenetic mechanisms are mitotically, and in some cases meiotically, heritable changes in the genome through non-DNA sequence coding processes that alter gene expression as a result of variable changes in environmental stimuli. Genome-wide association studies have been inconsistent in elucidating the association between genes and suicidal behavior, thereby making the heritability of suicidal behavior is unclear. However, recent epigenetic studies have provided evidence that epigenetic mechanisms could deliver the missing link between the heritability of suicidal behavior and the interaction between environment and the genome. The present review provides an in-depth discussion of epigenetic mechanisms that may regulate gene expression in suicidal behavior. The findings of current epigenetic studies on suicidal behavior will also be discussed considering future epigenome-wide association studies on elucidating the contributions of environment and genome on suicidal behavior.

Associations between avoidant focused coping strategies and polymorphisms in genes coding for brain-derived neurotrophic factor and vascular endothelial growth factor in suicide attempters: a preliminary study

In this study we investigated whether single nucleotide polymorphisms (SNP) in the genes coding for BDNF (Val66Met) and VEGF (C2578A) may be associated with maladaptive strategies among suicide attempt patients. We found that BDNF Val66Met gene polymorphism probably affect avoidant coping strategies.

Association of BDNF promoter methylation and genotype with suicidal ideation in elderly Koreans

OBJECTIVES

Brain-derived neurotrophic factor (BDNF) has been considered a risk factor for suicidal behavior in adult populations. BDNF secretion is influenced by epigenetic (DNA promoter methylation) and genetic (val66met polymorphism) profiles. We investigated the independent and interactive effects of BDNF methylation status and val66met polymorphisms on late-life suicidal ideation.

METHODS

In total, 732 Korean community residents aged 65+ years were evaluated; of 639 without suicidal ideation, 579 (90.6%) were followed up 2 years later. The prevalence and incidence of suicidal ideation were ascertained using the Geriatric Mental State Schedule. Sociodemographic and clinical covariates included age, sex, education, depressive symptoms, cognitive function, and disability. The independent effects of BDNF methylation status on the prevalence and incidence of suicidal ideation were investigated using multivariate logistic regression models. The two-way interactions of BDNF methylation status and val66met polymorphism on suicidal ideation were assessed using the same models.

RESULTS

Higher BDNF methylation status was significantly associated with both prevalence and incidence of suicidal ideation, independent of potential covariates. No significant methylation-genotype interaction was found.

CONCLUSIONS

The BDNF hypothesis and the epigenetic origin of the suicidal behavior were supported, even in old age. BDNF promoter methylation status may be useful as a biological marker for suicidality in late life.

Epigenetic and epistatic interactions between serotonin transporter and brain-derived neurotrophic factor genetic polymorphism: insights in depression

Epidemiological studies have shown significant results in the interaction between the functions of brain-derived neurotrophic factor (BDNF) and 5-HT in mood disorders, such as major depressive disorder (MDD). The latest research has provided convincing evidence that gene transcription of these molecules is a target for epigenetic changes, triggered by stressful stimuli that starts in early childhood and continues throughout life, which are subsequently translated into structural and functional phenotypes culminating in depressive disorders. The short variants of 5-HTTLPR and BDNF-Met are seen as forms which are predisposed to epigenetic aberrations, which leads individuals to a susceptibility to environmental adversities, especially when subjected to stress in early life. Moreover, the polymorphic variants also feature epistatic interactions in directing the functional mechanisms elicited by stress and underlying the onset of depressive disorders. Also emphasized are works which show some mediators between stress and epigenetic changes of the 5-HTT and BDNF genes, such as the hypothalamic-pituitary-adrenal (HPA) axis and the cAMP response element-binding protein (CREB), which is a cellular transcription factor. Both the HPA axis and CREB are also involved in epistatic interactions between polymorphic variants of 5-HTTLPR and Val66Met. This review highlights some research studying changes in the epigenetic patterns intrinsic to genes of 5-HTT and BDNF, which are related to lifelong environmental adversities, which in turn increases the risks of developing MDD.

Stress and trauma: BDNF control of dendritic-spine formation and regression

Chronic restraint stress leads to increases in brain derived neurotrophic factor (BDNF) mRNA and protein in some regions of the brain, e.g. the basal lateral amygdala (BLA) but decreases in other regions such as the CA3 region of the hippocampus and dendritic spine density increases or decreases in line with these changes in BDNF. Given the powerful influence that BDNF has on dendritic spine growth, these observations suggest that the fundamental reason for the direction and extent of changes in dendritic spine density in a particular region of the brain under stress is due to the changes in BDNF there. The most likely cause of these changes is provided by the stress initiated release of steroids, which readily enter neurons and alter gene expression, for example that of BDNF. Of particular interest is how glucocorticoids and mineralocorticoids tend to have opposite effects on BDNF gene expression offering the possibility that differences in the distribution of their receptors and of their downstream effects might provide a basis for the differential transcription of the BDNF genes. Alternatively, differences in the extent of methylation and acetylation in the epigenetic control of BDNF transcription are possible in different parts of the brain following stress. Although present evidence points to changes in BDNF transcription being the major causal agent for the changes in spine density in different parts of the brain following stress, steroids have significant effects on downstream pathways from the TrkB receptor once it is acted upon by BDNF, including those that modulate the density of dendritic spines. Finally, although glucocorticoids play a canonical role in determining BDNF modulation of dendritic spines, recent studies have shown a role for corticotrophin releasing factor (CRF) in this regard. There is considerable improvement in the extent of changes in spine size and density in rodents with forebrain specific knockout of CRF receptor 1 (CRFR1) even when the glucocorticoid pathways are left intact. It seems then that CRF does have a role to play in determining BDNF control of dendritic spines.

Investigating the role of BDNF and CCK system genes in suicidality in a familial bipolar cohort

BACKGROUND

Suicidal behaviour is a phenotype widely associated with psychiatric disorders such as major depressive disorder and bipolar disorder. However, recent evidence indicates that part of the heritability of suicidal behaviour is independent of the heritability of individual psychiatric disorders. This allows investigation into genetic risk factors for suicidal behaviour within a disorder using a candidate gene association approach.

METHODS

We used family-based association testing in a cohort of 130 multiplex bipolar pedigrees, comprising 795 individuals, to look for associations between suicidal behaviour and 32 single nucleotide polymorphisms (SNPs) from across the genes brain-derived neurotrophic factor (BDNF), cholecystokinin (CCK) and the cholecystokinin beta-receptor (CCKBR).

RESULTS

We found associations (p≤0.05) between suicide attempt and 12 SNPs of CCKBR and five SNPs of BDNF. After correction for multiple testing, seven SNPs of CCKBR remained significantly associated. No association was found between CCK and suicidal behaviour.

LIMITATIONS

The study relied on retrospective self-reporting by individuals to determine phenotype, and the sample size was relatively small.

CONCLUSIONS

The results of the study support the hypothesis that some CCKBR polymorphisms may contribute to an underlying predisposition towards suicidal behaviour in bipolar disorder.