Genetic and environmental pathways to suicidal behavior: Reflections of a genetic epidemiologist

Mediating effect of genome-wide DNA methylation on suicidal ideation induced by stressful events

OBJECTIVE

Schizophrenia is a debilitating disease that is associated with higher rates of death by unnatural causes including suicide. Exposure to stressful events is an important risk factor for suicidal ideation (SI); however, the mechanisms that link stress, SI, and suicide remain unclear. Epigenetic processes are involved in both vulnerability to suicidal behavior and stress. Therefore, we sought to study the relationship between epigenetic modifications and suicidal behavior and stress.

METHODS

This pilot study was conducted on 39 patients diagnosed with schizophrenia (54% men and age 45.5 ± 12.7). We analyzed the effects of (a) stress exposure and (b) the mediation of DNA methylation [via an epigenetic wide association study (EWAS) of more than 450 000 CpG sites across the genome] on SI severity.

RESULTS

The top CpG site mediating the effect of global stress exposure on SI was cg27660192 located in an intergenic region on chromosome 11, exerting a facilitating effect on worsening SI through DNA hypomethylation.

CONCLUSION

These preliminary results indicate that DNA methylation in peripheral tissues can shed light on the complex relationship between stress and SI in schizophrenia.

Global DNA methylation in suicidal ideation and suicide attempt in schizophrenia

Suicidal behavior is influenced by many risk factors such as childhood trauma, stressful life events, genetic factors, and severe mental illnesses. Suicidal ideation is present in 50% of schizophrenia patients and is associated with an elevated risk of suicide attempt. Studies have shown that epigenetic mechanisms are associated with suicidal behavior in schizophrenia. Although several studies have suggested the importance of epigenetic factors in suicidal ideation and behavior, no studies have investigated global methylation in association with these two phenotypes. This study investigated global methylation level/change in association with current and emergent suicidal ideation and also with suicide attempt. Forty-seven schizophrenia patients were assessed for the association between global methylation and suicide attempt, and a subsample of these patients (n = 27) was assessed for current suicidal ideation. Afterwards, we performed a longitudinal analysis in which global methylation changes during a 3-month follow-up were compared between patients with and without emergent suicidal ideation. This methylation analysis did not find evidence for a significant association between global methylation and suicidal ideation or suicide attempt. To date, there are no robust biomarkers predicting suicidal ideation or behavior in psychotic patients. This study is the first to investigate global methylation in predicting suicidal ideation and behavior. Although we did not find evidence for an association between global methylation and these phenotypes, our findings may offer novel insights into the molecular mechanisms linked to suicide. Future investigation may measure global methylation in association with suicidal ideation or behavior in larger samples.

Genome-wide methylation association with current suicidal ideation in schizophrenia

In this study, we investigate the epigenetic mechanisms associated with current suicidal ideation. Gene expression changes have been found in post-mortem brain of suicide victims. However, it is not clear how in-vivo gene expression change confers risk for suicide. DNA methylation is a form of epigenetic modification that regulates gene expression. Our primary aim is to investigate genome-wide methylation in conferring risk for current suicidal ideation (SI) in schizophrenia. The presence of current SI and genome-wide methylation patterns were assessed in 107 patients with schizophrenia. DNA methylation has been measured in white blood cells as a possible peripheral biomarker of SI. SI was the primary outcome variable in a model including methylation status of white blood cells using the Illumina 450 array. We have tested the association with genome-wide methylation levels in 19 subjects with current SI and 88 subjects without current SI and we found that higher methylation level in the CpG cg06121808 located in the gene SLC20A1 on chromosome 2 was associated with current SI (p = 0.000003; beta difference = 0.06). Furthermore, the distal promoter analysis showed that the gene SMPD2 was hypermethylated in suicide ideators (p = 0.0001; beta difference = 0.02). Thus, molecular biomarkers could advance our understanding of the molecular mechanisms of stress-related SI. Furthermore, the methylation sites that we have identified should be replicated in other suicide related phenotypes to generate robust biomarkers with high translational value for proof of concept interventions aiming at reducing SI.

Suicide: Genetics and Heritability

Nature vs nurture is, and has been, a never stopping debate since Lamarck and Darwin exposed their corresponding theories on evolution, and even before them, such discussion already existed. Is suicide a heritable conduct? Is it learnt? Maybe the answer is both and none, at the same time. From genetic twin studies to epigenetic and environmental influence on development, this chapter aims to take a look at different points of view and most relevant theories in one of the worlds leading causes of death, specially for young individuals. We explore different studies aiming to find biomarkers for suicide, as well as other traits frequently encountered in individuals who engage in suicidal behavior, such as impulsivity, aggressivity, and hopelessness. Finally, this chapter also looks at some of the most recent approaches in treatment and prevention of suicidal behavior, in order to highlight what they have in common and try to explain (at least partially) why they could be effective.

Suicidal behavior and stress generation in adolescents

Stress generation has potential to account for recurrent suicidal behavior. The current study represents a first step toward evaluating this possibility in a sample of adolescent psychiatric inpatients (n = 99; 79.80% female) followed over six months. At index admission, participants completed baseline measures of depressive symptom severity, suicidal ideation, lifetime history of suicide attempts, and negative life events using a contextual threat life stress interview. Negative life events since baseline were assessed at the follow-up assessment. Consistent with the stress generation hypothesis, lifetime number of suicide attempts prospectively predicted higher rates of dependent, but not independent, stress. Bayesian analyses also yielded substantial support for an association with overall dependent stress, but provided more modest support for specificity to this form of life stress relative to independent stress. Implications of these findings and directions for future research further clarifying the role of stress generation in suicidal behavior are discussed.

Overlapping genetic effects between suicidal ideation and neurocognitive functioning

BACKGROUND

Suicide is the second leading cause of death among adolescents and young adults. Several studies have indicated significant genetic influences on suicide-related phenotypes and mounting evidence from neurobiological research has linked deficits in neurocognitive abilities to suicide phenotypes. The goal of the present study was to estimate the heritability of suicidal ideation (SI) in a large sample of adolescents and determine if SI is genetically correlated with neurocognitive functioning.

METHODS

Genome-wide data (N = 3564 unrelated individuals of European Ancestry) were drawn from the Philadelphia Neurodevelopment Cohort. Adolescents completed a psychiatric assessment, as well as a computerized neurocognitive battery to assess performance across four domains: memory, executive function, social cognition, and complex cognition. Genomic-relatedness-matrix restricted maximum likelihood (GREML) estimation was used to determine SNP-heritability (h²_SNP) of SI and the genetic correlation (r_G) between SI and neurocognitive domains.

RESULTS

Nearly 17% of adolescents reported SI. The SNP-heritability estimate for SI was marginally significant (h²_SNP = 11%, SE = 8%, p = 0.086). Bivariate analyses indicated a significant r_G between SI and emotion identification (r_G = 0.79, SE = 0.45, p = 0.006; phenotypic correlation r = 0.04, p = 0.017).

LIMITATIONS

It is possible that SI may represent a related, but differentially heritable construct from suicide attempts/completion and other comorbid psychopathology. Additionally, though genetic correlations point to shared genetic factors across traits, direct causal mechanisms cannot be deduced.

CONCLUSIONS

Common heritable factors contribute to variation in SI and neurocognitive functioning. Genetic factors influencing emotion identification have significant genetic overlap with SI.

Identification of novel genome-wide associations for suicidality in UK Biobank, genetic correlation with psychiatric disorders and polygenic association with completed suicide

BACKGROUND

Suicide is a major issue for global public health. Suicidality describes a broad spectrum of thoughts and behaviours, some of which are common in the general population. Although suicide results from a complex interaction of multiple social and psychological factors, predisposition to suicidality is at least partly genetic.

METHODS

Ordinal genome-wide association study of suicidality in the UK Biobank cohort comparing: 'no suicidality' controls (N = 83,557); 'thoughts that life was not worth living' (N = 21,063); 'ever contemplated self-harm' (N = 13,038); 'act of deliberate self-harm in the past' (N = 2498); and 'previous suicide attempt' (N = 2666).

OUTCOMES

We identified three novel genome-wide significant loci for suicidality (on chromosomes nine, 11 and 13) and moderate-to-strong genetic correlations between suicidality and a range of psychiatric disorders, most notably depression (r_g 0·81).

INTERPRETATION

These findings provide new information about genetic variants relating to increased risk of suicidal thoughts and behaviours. Future work should assess the extent to which polygenic risk scores for suicidality, in combination with non-genetic risk factors, may be useful for stratified approaches to suicide prevention at a population level. FUND: UKRI Innovation-HDR-UK Fellowship (MR/S003061/1). MRC Mental Health Data Pathfinder Award (MC_PC_17217). MRC Doctoral Training Programme Studentship at the University of Glasgow (MR/K501335/1). MRC Doctoral Training Programme Studentship at the Universities of Glasgow and Edinburgh. UKRI Innovation Fellowship (MR/R024774/1).

A Longitudinal Study of Racial Discrimination and Risk for Death Ideation in African American Youth

Although multiple studies have found that African Americans commonly experience racial discrimination, available studies have yet to examine how perceived racism might be related to suicide vulnerability in African American youth. The purpose of this study was to examine a framework for how perceived racial discrimination contributes to symptoms of depression and anxiety as well as subsequent suicide ideation and morbid ideation. Data were obtained from 722 African American youth at mean age 10.56 years (SD = 0.64); a second wave of data was obtained 2 years later. Results revealed both a direct effect and mediated effects of perceived racism on later suicide and morbid ideation. For boys and girls, the effect of perceived racism was mediated by symptoms of depression. However, the association was mediated by anxiety for girls, but not for boys in the current sample. Implications for future research and interventions are discussed.

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.

Differences by gender in completed suicides in a Mexican population: A psychological autopsy study

OBJECTIVE

Using the method of psychological autopsy, we identified differences by gender in socio-demographic aspects, signs and symptoms, and suicide characteristics in a population of the state of Tabasco. Mexico.

METHODS

Between the years 2007-2014, 182 psychological autopsies were documented by the Secretary of Health of the State of Tabasco, Mexico. A structured questionnaire was used to obtain information on socio-demographic aspects and suicide characteristics.

RESULTS

The sample was mainly formed by males (78%). 84% of the sample used hanging as suicide method. However, in comparison with the male group, females were older on the average (p = 0.002); they were mostly housewives (37.5%) and had more years of schooling (p = 0.004). Other significant differences predominantly present in the male group were: the use of alcohol at the time of suicide (52.1%), job retirement, and increases in apathy (50.7%) and aggressiveness (36.6%) (p < 0.05).

CONCLUSION

Our results suggest that there are differences by gender between subjects with completed suicide. Factors such as alcohol consumption, job retirement, aggressiveness and isolation/social apathy certainly render men more vulnerable to suicide in the Mexican population.

Neurodevelopmental sequelae associated with gray and white matter changes and their cellular basis: A comparison between Autism Spectrum Disorder, ADHD and dyslexia

Many psychiatric diseases, such as major depression and schizophrenia, are accompanied by patterns of gray matter and white matter changes in the cortex that may be due to structural pathologies of synapses and their dendrites in the gray matter on the one hand and to pathologies in myelinating oligodendrocytes on the other. Here the possibility has been briefly examined that such a generalization might also hold for Autistic Spectrum Disorders (ASD). Evidence is presented that gray matter changes that accompany ASD may in fact reflect changes in synapses and subsequently of their dendrites, whereas those in the white matter reflect changes in myelination due to pathologies of oligodendrocytes. It is proposed that such structural pathologies during development provide a coherent biological model not only for the onset and course of ASD but also provide the basis for development and systematic evaluation of new treatment strategies.

A 2-year psychological autopsy study of completed suicides in the athens greater area, Greece

OBJECTIVE

To study the characteristics of a sample of suicide victims from the Athens Greater Area using the psychological autopsy method for the first time in Greece.

METHODS

We studied all recorded cases of completed suicide for the 2-year time period November 2007-October 2009 collecting data from the victims' forensic records as well as from the completion of a psychological autopsy questionnaire.

RESULTS

335 persons were recorded as suicide victims. We contacted relatives of 256 victims interviewing those of 248 of them (96.9%). The differences regarding sex, marital and employment status between our sample and the general population were statistically significant (p<0.001). The male/female ratio was 3:1. Comparatively more victims were divorced, separated or single and a greater proportion were pensioners or unemployed. 26.0% of the victims had history of prior attempts (64.4% once, 20.3% twice and 15.3% more times). 42.6% were taking psychiatric medication-significantly more women than men according to blood tests; 14.2% had been hospitalized in a psychiatric clinic the year prior to their death. 84.8% have deceased at the place of suicide and 15.2% died in the hospital; 80.3% died indoors and 19.7% outdoors. Men died primarily by hanging or shooting by a firearm while women preferred jumping from height instead (p<0.001). As many as 48.8% had expressed their intention to die to their relatives; 26.6% left a suicide note.

CONCLUSION

Our study has shown that the psychological autopsy method is applicable and widely accepted yielding results comparable to the international literature. Specific parameters associated with suicide have been studied for the first time in Greece.

Genome-wide association studies of suicidal behaviors: a review

Suicidal behaviors represent a fatal dimension of mental ill-health, involving both environmental and heritable (genetic) influences. The putative genetic components of suicidal behaviors have until recent years been mainly investigated by hypothesis-driven research (of "candidate genes"). But technological progress in genotyping has opened the possibilities towards (hypothesis-generating) genomic screens and novel opportunities to explore polygenetic perspectives, now spanning a wide array of possible analyses falling under the term Genome-Wide Association Study (GWAS). Here we introduce and discuss broadly some apparent limitations but also certain developing opportunities of GWAS. We summarize the results from all the eight GWAS conducted up to date focused on suicidality outcomes; treatment emergent suicidal ideation (3 studies), suicide attempts (4 studies) and completed suicides (1 study). Clearly, there are few (if any) genome-wide significant and reproducible findings yet to be demonstrated. We then discuss and pinpoint certain future considerations in relation to sample sizes, the units of genetic associations used, study designs and outcome definitions, psychiatric diagnoses or biological measures, as well as the use of genomic sequencing. We conclude that GWAS should have a lot more potential to show in the case of suicidal outcomes, than what has yet been realized.

Catechol-O-methyltransferase Val158Met polymorphism and altered COMT gene expression in the prefrontal cortex of suicide brains

Catechol-O-methyltransferase (COMT) plays a key role in the degradation of catecholamine neurotransmitters within the brain. A functional polymorphism COMT Val158Met has been associated with psychiatric disorders including suicidal behavior. In the present study we examined whether this polymorphism was related to COMT mRNA expression in frontal cortical regions, and whether the expression of COMT differed between depressed suicide victims and psychiatric healthy controls. The Val158Met polymorphism was determined by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) analysis. The levels of COMT mRNA expression in the frontopolar cortex (FPC; 29 suicides vs. 27 controls) and orbital frontal cortex (OFC; 19 suicides vs. 15 controls) were significantly increased among depressed individuals that died by suicide relative to those of controls, being up-regulated by approximately 60% and 65% in the FPC and OFC, respectively. Furthermore, among individuals with the Met allele (Met/Met and Met/Val genotypes) who died by suicide COMT mRNA expression was elevated relative to that of the nondepressed Met allele carriers. However, significant differences were not detected between suicides (n=49) and controls (n=72) with respect to the Val158Met genotypic distribution and allelic frequencies. These results are consistent with the perspective that altered COMT mRNA expression in frontal cortical brain regions might contribute to suicide and/or depression, further supporting the role of dysregulation of catecholaminergic pathway genes in the pathophysiology of suicide behaviors.

Characterizing alcohol use disorders and suicidal ideation in young women

OBJECTIVE

Alcohol use disorders (AUDs) and suicidal ideation (SI) co-occur, yet few studies have investigated the risk and protective factors that infl uence their comorbidity.

METHOD

Data from 3,787 twin women ages 18`27 years were analyzed. AUD was defined as a lifetime history of alcohol abuse or dependence as defined in the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. SI was coded as a lifetime report of any SI, and all subjects were queried about SI. Subjects were divided into those with neither AUD nor SI (AUD-SI-), those with AUD but no SI (AUD+SI-), those with SI but no AUD (AUD-SI+), and those with comorbid AUD and SI (AUD+SI+). Association with multiple measures of psychopathology, negative life events, personality, and family history was assessed using multinomial logistic regression.

RESULTS

Women with AUD were at 3.1 (95% confidence interval [2.5, 3.8]) odds of also reporting a lifetime history of SI. Psychopathology and negative life events were consistently high in the AUD+SI+ group. AUD+SI+ women also were more likely to report drinking to cope. Substance use was more common in the AUD+SI- versus the AUD-SI+ women, whereas major depressive disorder, social phobia, and panic attacks were more commonly reported by the AUD-SI+ versus the AUD+SI- women.

CONCLUSIONS

The comorbidity between AUD and SI is characterized in young women by co-occurring psychopathology, drinking to cope, and negative life events.

Suicide in the US Army

Suicide in the US Army is a high-profile public health problem that is complex and poorly understood. Adding to the confusion surrounding Army suicide is the challenge of defining and understanding individuals/populations dying by suicide. Data from recent studies have led to a better understanding of risk factors for suicide that may be specifically associated with military service, including the impact of combat and deployment on increased rates of psychiatric illness in military personnel. The next steps involve applying these results to the development of empirically supported suicide prevention approaches specific to the military population. This special article provides an overview of suicide in the Army by synthesizing new information and providing clinical pearls based on research evidence.

The European Psychiatric Association (EPA) guidance on suicide treatment and prevention

Suicide is a major public health problem in the WHO European Region accounting for over 150,000 deaths per year. SUICIDAL CRISIS: Acute intervention should start immediately in order to keep the patient alive.

DIAGNOSIS

An underlying psychiatric disorder is present in up to 90% of people who completed suicide. Comorbidity with depression, anxiety, substance abuse and personality disorders is high. In order to achieve successful prevention of suicidality, adequate diagnostic procedures and appropriate treatment for the underlying disorder are essential.

TREATMENT

Existing evidence supports the efficacy of pharmacological treatment and cognitive behavioural therapy (CBT) in preventing suicidal behaviour. Some other psychological treatments are promising, but the supporting evidence is currently insufficient. Studies show that antidepressant treatment decreases the risk for suicidality among depressed patients. However, the risk of suicidal behaviour in depressed patients treated with antidepressants exists during the first 10-14 days of treatment, which requires careful monitoring. Short-term supplementary medication with anxiolytics and hypnotics in the case of anxiety and insomnia is recommended. Treatment with antidepressants of children and adolescents should only be given under supervision of a specialist. Long-term treatment with lithium has been shown to be effective in preventing both suicide and attempted suicide in patients with unipolar and bipolar depression. Treatment with clozapine is effective in reducing suicidal behaviour in patients with schizophrenia. Other atypical antipsychotics are promising but more evidence is required. TREATMENT TEAM: Multidisciplinary treatment teams including psychiatrist and other professionals such as psychologist, social worker, and occupational therapist are always preferable, as integration of pharmacological, psychological and social rehabilitation is recommended especially for patients with chronic suicidality. FAMILY: The suicidal person independently of age should always be motivated to involve family in the treatment. SOCIAL SUPPORT: Psychosocial treatment and support is recommended, as the majority of suicidal patients have problems with relationships, work, school and lack functioning social networks.

SAFETY

A secure home, public and hospital environment, without access to suicidal means is a necessary strategy in suicide prevention. Each treatment option, prescription of medication and discharge of the patient from hospital should be carefully evaluated against the involved risks. TRAINING OF PERSONNEL: Training of general practitioners (GPs) is effective in the prevention of suicide. It improves treatment of depression and anxiety, quality of the provided care and attitudes towards suicide. Continuous training including discussions about ethical and legal issues is necessary for psychiatrists and other mental health professionals.

Familial clustering of suicide risk: a total population study of 11.4 million individuals

BACKGROUND

Research suggests that suicidal behaviour is aggregated in families. However, due to methodological limitations, including small sample sizes, the strength and pattern of this aggregation remains uncertain.

METHOD

We examined the familial clustering of completed suicide in a Swedish total population sample. We linked the Cause of Death and Multi-Generation Registers and compared suicide rates among relatives of all 83 951 suicide decedents from 1952-2003 with those among relatives of population controls.

RESULTS

Patterns of familial aggregation of suicide among relatives to suicide decedents suggested genetic influences on suicide risk; the risk among full siblings (odds ratio 3.1, 95% confidence interval 2.8-3.5, 50% genetic similarity) was higher than that for maternal half-siblings (1.7, 1.1-2.7, 25% genetic similarity), despite similar environmental exposure. Further, monozygotic twins (100% genetic similarity) had a higher risk than dizygotic twins (50% genetic similarity) and cousins (12.5% genetic similarity) had higher suicide risk than controls. Shared (familial) environmental influences were also indicated; siblings to suicide decedents had a higher risk than offspring (both 50% genetically identical but siblings having a more shared environment, 3.1, 2.8-3.5 v. 2.0, 1.9-2.2), and maternal half-siblings had a higher risk than paternal half-siblings (both 50% genetically identical but the former with a more shared environment). Although comparisons of twins and half-siblings had overlapping confidence intervals, they were supported by sensitivity analyses, also including suicide attempts.

CONCLUSIONS

Familial clustering of suicide is primarily influenced by genetic and also shared environmental factors. The family history of suicide should be considered when assessing suicide risk in clinical settings or designing and administering preventive interventions.