Role of serotonergic-related systems in suicidal behavior: Data from a case-control association study

Apolipoproteins and Suicide: A Potential Psychiatric Biomarker

Every year around 800,000 people commit suicide, this represents one death every 40 s. In the search for possible biological biomarkers associated with suicide and/or psychiatric disorders, serum cholesterol levels have been extensively explored. Several studies indicate that cholesterol and associated proteins, especially apolipoproteins (Apos), may play an important role in the diagnosis, prognosis, and susceptibility of suicidal behavior. Here, we describe the current knowledge and findings in the relationship between apolipoproteins and suicide.HIGHLIGHTSThis is the first systematic review of Apos in relation to suicidal behavior.Dysregulations of Apos expression has been observed in patients with suicidal behavior.Apos seem to be associated with cognitive dysfunction in suicide attempters.ApoE is a potential biomarker regarding suicidal behavior.

Fight the Fire: Association of Cytokine Genomic Markers and Suicidal Behavior May Pave the Way for Future Therapies

The fight against suicide is highly challenging as it may be one of the most complex and, at the same time, most threatening among all psychiatric phenomena. In spite of its huge impact, and despite advances in neurobiology research, understanding and predicting suicide remains a major challenge for both researchers and clinicians. To be able to identify those patients who are likely to engage in suicidal behaviors and identify suicide risk in a reliable and timely manner, we need more specific, novel biological and genetic markers/indicators to develop better screening and diagnostic methods, and in the next step to utilize these molecules as intervention targets. One such potential novel approach is offered by our increasing understanding of the involvement of neuroinflammation based on multiple observations of increased proinflammatory states underlying various psychiatric disorders, including suicidal behavior. The present paper overviews our existing understanding of the association between suicide and inflammation, including peripheral and central biomarkers, genetic and genomic markers, and our current knowledge of intervention in suicide risk using treatments influencing inflammation; also overviewing the next steps to be taken and obstacles to be overcome before we can utilize cytokines in the treatment of suicidal behavior.

Genetic variations related to inflammation in suicidal ideation and behavior: A systematic review

BACKGROUND/OBJECTIVES

Immune-inflammatory changes have been found in all types of suicidal ideation and behavior (SIB), independently of associated mental disorders. Since several Single Nucleotide Polymorphisms (SNPs) affect the function of inflammation-related genes, we searched the literature for genetic variations potentially altering inflammatory processes in SIB.

METHODS

We included studies that looked for associations between SIB and SNPs in genes related to inflammatory processes. Case reports, literature reviews, and animal studies were excluded. Articles were retrieved from PubMed and PsycINFO databases, Google Scholar and GreySource Index until September 17th, 2022. Quality was assessed using Q-Genie.

RESULTS

We analyzed 32 studies. SIB has been associated with eighteen SNPs located in genes encoding for interleukin-8 (rs4073), C-reactive protein (rs1130864), tumor necrosis factor α (rs1800629, rs361525, and rs1099724), tumor necrosis factor receptor 2 (rs1061622), transforming growth factor β-1 (rs1982073), acid phosphatase 1 (rs7419262, rs300774), interleukin-10 (rs1800896), interferon γ (rs2430561), amino-carboxy muconate semialdehyde decarboxylase (rs2121337), interleukin 7 (rs10448044, rs10448042), macrophage migration inhibitory factor (rs755622), interleukin 1-α (rs1800587), and interleukin 1-β (rs1143634 and rs16944. A genome-wide association study reported one association at the threshold of significance with the rs300774 SNP, located in the 2p25 region containing ACP1 gene.

DISCUSSION

The studies included were methodologically and clinically diverse and of moderate quality. Their findings suggest that some inflammation-related SNPs could increase the likelihood of SIB but the evidence to date is insufficient. Further research using gene-gene (GxG) and gene-environment (GxE) approaches is warranted.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk], identifier [CRD42022296310].

The role of the 5-HTTLPR polymorphism in acquired capability for suicide

OBJECTIVE

According to the Interpersonal Psychological Theory of Suicide, capability for suicide comprises two dimensions: fearlessness about death and elevated pain tolerance. The short (S) allelic variant of the serotonin transporter gene-linked polymorphic region (5-HTTLPR) has repeatedly been associated with more violent and lethal suicide methods and lethality of suicide attempts. The current study aimed to investigate whether 5-HTTLPR allelic variants are associated with fearlessness about death and pain tolerance/persistence and whether it moderates the relationship between childhood maltreatment and acquired capability for suicide.

METHOD

A cohort of 208 inpatients hospitalized due to a recent suicide attempt or severe suicidal ideation was genotyped for the 5-HTTLPR and assessed for childhood maltreatment. Subjective pain tolerance and fearlessness about death as well as objective pain persistence was assessed using a pressure algometer.

RESULTS

Fearlessness about death, pain tolerance, and pain persistence did not differ between 5-HTTLPR genotypes. However, there was a significant correlation between self-reported childhood maltreatment and fearlessness about death that emerged exclusively in homozygous S-allele carriers.

CONCLUSION

Results suggest that there are no "high-risk"-alleles that generally increase capability for suicide. However, in terms of future suicide-related behaviors exposure to childhood maltreatment events could exert a particularly negative influence on homozygous S-allele carriers by increasing their fearlessness about death.

Associations Among Monoamine Neurotransmitter Pathways, Personality Traits, and Major Depressive Disorder

Major depressive disorder (MDD) is a complex psychiatric disease requiring multidisciplinary approaches to identify specific risk factors and establish more efficacious treatment strategies. Although the etiology and pathophysiology of MDD are not clear until these days, it is acknowledged that they are almost certainly multifactorial and comprehensive. Monoamine neurotransmitter system dysfunction and specific personality traits are independent risk factors for depression and suicide. These factors also demonstrate complex interactions that influence MDD pathogenesis and symptom expression. In this review, we assess these relationships with the aim of providing a reference for the development of precision medicine.

Rare variants in SLC6A4 cause susceptibility to major depressive disorder with suicidal ideation in Han Chinese adolescents and young adults

BACKGROUND

Suicidal ideation (SI) is the most serious symptom of major depressive disorder (MDD) and considered an extreme state. The serotonin transporter gene (SLC6A4) plays a significant role in MDD and suicide pathophysiology. Previous studies have revealed an association between common variants of SLC6A4 with the risk of MDD and suicide. However, very few studies have so far focused on the degree to which rare variants of SLC6A4 are responsible for the depression observed in adolescent and young adult suicide patients. The aim of this study was to examine the impact of common and rare variants of SLC6A4 on the risk of Han Chinese adolescents and young adults suffering MDD with SI.

METHODS

Targeted sequencing of the SLC6A4 gene was conducted using FastTarget technology in Han Chinese adolescents and young adults, of which 74 were MDD patients with SI and 150 were healthy controls. Gene-based association analyses of rare variants were performed using enrichment analysis and a cumulative allele test. An allele association study was performed against common variants.

RESULTS

After sequencing and bioinformatics analysis, a total of 15 single nucleotide variants (SNVs) were detected in the targeted regions from all participants, including 9 common and 6 rare variants. Among these, 5 rare variants were identified within the study group. Enrichment analysis of rare variants demonstrated a statistical difference (p = 0.042) between the study and control groups. Using cumulative allele analysis, alternative alleles in the SLC6A4 gene exhibited an association with MDD patients with SI (cumulative allele: OR = 10.18, 95% CI = 1.18-87.32, p = 0.017). No significant association was found between the 9 common SLC6A4 variants and MDD patients with SI.

CONCLUSIONS

Our results suggest that rare variants of SLC6A4 may contribute to a genetic risk of adolescents and young adults suffering MDD with SI.

Association of polymorphisms in HTR2A, TPH1, and TPH2 genes with attempted suicide in rural China

OBJECTIVE

We aimed to test the association of polymorphisms in HTR2A, TPH1, and TPH2 genes with attempted suicide in rural China.

PARTICIPANTS AND METHODS

On the basis of a case-control study, we recruited 1200 pairs of participants from Shandong Province, China. The blood samples of 712 suicide attempters and 739 nonsuicide attempters were collected finally. We tested seven single nucleotide polymorphisms: rs6313 and rs6311 in HTR2A, rs4537731, rs1800532, and rs1799913 in TPH1, and rs4448731 and rs4641527 in TPH2.

RESULTS

In univariate analysis, allele C of rs4537731 was associated negatively with attempted suicide among total and male samples; however, the association was not statistically significant in multivariate analysis after adjusting for other potential confounding factors. No association between other six single nucleotide polymorphisms and attempted suicide was found in the total, male, or female samples.

CONCLUSION

This study did not support the effect of these seven serotonergic gene polymorphisms on attempted suicide in rural China.

The influence of the serotonin transporter gene 5-HTTLPR polymorphism on suicidal behaviors: a meta-analysis

Suicidal Behavior (SB) is the second leading cause of death among youths worldwide and the tenth among all age groups. Inherited genetic differences have a role in suicidality with heritability ranging from 30 to 55%. The SLC6A4 5-HTTLPR gene variant has been largely investigated for association with SB, with controversial results. In this work, we sought to determine whether the results of previous meta-analyses were confirmed or modified subsequent to the inclusion of more recent literature data. An electronic literature search was performed to identify relevant studies published until July 2018. Data were analysed through RevMan v5.3. Subgroup and sensitivity meta-analyses were performed considering different SB sub-phenotypes, ethnicity, gender and psychiatric diagnostic categories. Our literature search yielded 1186 articles; among these, we identified 45 pertinent case-control studies (15,341 subjects). No association was found between low-expressing alleles or genotypes (S + L_G alleles or S' carrier genotypes) and SB in the primary analyses. However, low-expressing alleles (S + L_G) were associated with an increased risk of Violent Suicide Attempt (OR = 1.44, C.I. 1.17-1.78, p = .0007). An effect of the same alleles on SB was found in a subpopulation of substance abusers, but this result was not confirmed after the exclusion of healthy subjects from the control group. The other sensitivity meta-analyses did not show any significant effect. Our findings contribute to clarify the conflicting previous evidence by suggesting an association between the 5-HTTLPR and Violent SB. Nonetheless, many other modulators, including environmental factors and epigenetic mechanisms may act to further increase the level of complexity.

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.

The androgen model of suicide completion

Suicide is a devastating public health issue that imposes severe psychological, social, and economic burdens not only for the individuals but also for their relatives, friends, clinicians, and the general public. Among the different suicidal behaviors, suicide completion is the worst and the most relevant outcome. The knowledge of biological etiopathological mechanisms involved in suicide completion is limited. Hitherto, no objective markers, either alone or in combination, can reliably predict who will complete a suicide. However, such parameters are strongly needed to establish and optimize prediction and prevention. We introduce here a novel ideation-to-completion framework in suicide research and discuss the problems of studies aiming at identifying and validating clinically useful markers. The male gender is a specific risk factor for suicide, which suggests that androgen effects are implicated in the transition from suicidal ideation to suicide completion. We present multiple lines of direct and indirect evidence showing that both an increased prenatal androgen load (with subsequent permanent neuroadaptations) and increased adult androgen activity are involved in suicide completion. We also review data arguing that modifiable maternal behavioral traits during pregnancy contribute to the offspring's prenatal androgen load and increase the risk for suicide completion later in life. We conclude that in utero androgen exposure and adult androgen levels facilitate suicide completion in an synergistic manner. The androgen model of suicide completion provides the basis for the development of novel predictive and preventive strategies in the future.

[Genetics and epigenetics of suicidal behaviors]

With more than 10 000 deaths each year in France, suicide is a major public health problem. Despite many known risk factors, suicide prediction remains extremely difficult in daily clinical practice. The identification of biomarkers, including genetic and epigenetic factors, is needed in suicidology in order to better understand pathophysiology of such behaviors and to improve the screening of individuals at high suicidal risk. Numerous studies have reported candidate genes involved in serotonergic system, HPA axis and neurotrophic system. Moreover, an interaction between genetic factors and environment is now admitted, facilitating emergence of a psychobiological vulnerability leading to the suicidal act. For instance, polymorphism of the serotonin transporter (5-HTTLPR) as well as its interaction with early life events (childhood abuse) are involved in suicidality in adulthood. Unfortunately pangenomic studies are not conclusive yet. Beyond serotonergic genes, the SKA-2 gene, which is involved in stress response, deserves more attention. SKA-2 genic expression and methylation level have been associated with the suicidal act. In the future, the combination of clinical, biological and genetic risk factors will probably improve detection of suicide risk.

Neuroinflammation in suicide: Toward a comprehensive model

OBJECTIVES

Suicidal behaviour (SB) entered the DSM-5, underlying a specific biological vulnerability. Then, recent findings suggested a possible role of the immune system in SB pathogenesis. The objective of this review is to present these main immune factors involved in SB pathogenesis.

METHODS

We conducted a review using Preferred Reporting Items for Systematic reviews and Meta-Analysis criteria, and combined ("Inflammation") AND ("Suicidal ideation" OR "Suicidal attempt" OR "suicide").

RESULTS

Post mortem studies demonstrated associations between suicide and inflammatory cytokines in the orbitofrontal cortex, a brain region involved in suicidal vulnerability. Also, microgliosis and monocyte-macrophage system activation may be a useful marker of suicide neurobiology. Kynurenine may influence inflammatory processes, and related molecular pathways may be involved in SB pathophysiology. Few recent studies associated inflammatory markers with suicidal vulnerability: serotonin dysfunction, impulsivity and childhood trauma. Interestingly, the perception of threat that leads suicidal individuals to contemplate suicide may activate biological stress responses, including inflammatory responses.

CONCLUSIONS

Translational projects would be crucial to identify a specific marker in SB disorders, to investigate its clinical correlations, and the interaction between inflammatory cytokines and monoamine systems in SB. These researches might lead to new biomarkers and novel directions for therapeutic strategies.

Predictors for self-directed aggression in Italian prisoners include externalizing behaviors, childhood trauma and the serotonin transporter gene polymorphism 5-HTTLPR

Suicidal behavior and self-mutilation can be regarded as the expression of self-directed aggression and both are common in prison populations. We investigated the influence of externalizing behaviors, depressive symptoms, childhood trauma, 5-HTTLPR variants on self-directed aggression (N = 145) in a group of 702 male Italian prisoners. Participants were comprehensively evaluated, including for psychiatric disorders, impulsive traits, lifetime aggressive behavior [Brown-Goodwin Lifetime History of Aggression (BGHA)], hostility, violent behavior during incarceration, depressive symptomatology [Hamilton Depression Rating Scale (HDRS)], childhood trauma [Childhood Trauma Questionnaire (CTQ)]. Logistic regression analysis showed false discovery rate corrected independent main effects of externalizing behaviors: BGHA (P = 0.001), violent behavior in jail (P = 0.007), extraversion (P = 0.015); HDRS (P = 0.0004), Axis I disorders (P = 0.015), CTQ (P = 0.004) and 5-HTTLPR genotype (P = 0.02). Carriers of 5-HTTLPR high (LA LA ), intermediate (LA LG , SLA ) activity variants were more likely to have exhibited self-directed aggression relative to the low activity (LG LG , SLG , SS) variant: high/low: odds ratio (OR) = 2.3, 95% confidence interval (CI) 1.27-4.68, P = 0.007; intermediate/low: OR = 1.96, 95% CI 1.09-3.68, P = 0.025. The CTQ main effect was driven by physical abuse. There was no interactive effect of 5-HTTLPR and CTQ. Secondary logistic regression analyses in (1) all suicide attempters (N = 88) and (2) all self-mutilators (N = 104), compared with controls showed that in both groups, childhood trauma (P = 0.008-0.01), depression (P = 0.0004-0.001) were strong predictors. BGHA, violent behavior in jail predicted self-mutilation (P = 0.002) but not suicide attempts (P = 0.1). This study was able to distinguish differing influences on self-directed aggression between groups of closely related predictor variables within the externalizing behavioral domain. 5-HTTLPR had an independent, variant dosage effect.

Plasma apolipoprotein E and severity of suicidal behaviour

There is evidence for association between low cholesterol levels and suicidal behaviour. Since apolipoprotein E (ApoE) is involved in the cholesterol metabolism in both the periphery and in the central nervous system; it may be of particular interest in the neurobiology of suicidal behaviour. Furthermore, hypothalamic-pituitary-adrenal (HPA) axis function, one of the main biological systems implicated in both suicidal behaviour and early-life adversity, affect ApoE levels. Very few studies have assessed plasma ApoE in relation to suicidal behaviour. The purpose of this study was to investigate levels of ApoE in plasma in relation to the severity of suicidal behaviour and life-time adversity in the form of exposure to interpersonal violence in suicide attempters. A total of 100 suicide attempters (67 women and 33 men) were enroled in the study. Information on earlier suicide attempts and age at onset of suicidal behaviour was gathered using the Karolinska Suicide History Interview. The Karolinska Interpersonal Violence Scale was used to assess exposure to interpersonal violence. Plasma ApoE was measured by immunonephelometry according to accredited routines. Patients with at least one earlier suicide attempt had significantly higher ApoE levels compared to suicide attempters debuting with suicidal behaviour at inclusion in the study. A higher number of earlier suicide attempts was significantly correlated with higher plasma ApoE levels. Age at onset was significantly negatively correlated with ApoE after adjusting for age. ApoE showed a significant positive correlation with exposure to interpersonal violence as a child in male suicide attempters. Our findings indicate that ApoE may be related to stress and trauma and the temporal severity of suicidal behaviour.

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.

Polymorphism in the serotonin receptor 2a (HTR2A) gene as possible predisposal factor for aggressive traits

Aggressive manifestations and their consequences are a major issue of mankind, highlighting the need for understanding the contributory factors. Still, aggression-related genetic analyses have so far mainly been conducted on small population subsets such as individuals suffering from a certain psychiatric disorder or a narrow-range age cohort, but no data on the general population is yet available. In the present study, our aim was to identify polymorphisms in genes affecting neurobiological processes that might explain some of the inter-individual variation between aggression levels in the non-clinical Caucasian adult population. 55 single nucleotide polymorphisms (SNP) were simultaneously determined in 887 subjects who also filled out the self-report Buss-Perry Aggression Questionnaire (BPAQ). Single marker association analyses between genotypes and aggression scores indicated a significant role of rs7322347 located in the HTR2A gene encoding serotonin receptor 2a following Bonferroni correction for multiple testing (p = 0.0007) both for males and females. Taking the four BPAQ subscales individually, scores for Hostility, Anger and Physical Aggression showed significant association with rs7322347 T allele in themselves, while no association was found with Verbal Aggression. Of the subscales, relationship with rs7322347 was strongest in the case of Hostility, where statistical significance virtually equaled that observed with the whole BPAQ. In conclusion, this is the first study to our knowledge analyzing SNPs in a wide variety of genes in terms of aggression in a large sample-size non-clinical adult population, also describing a novel candidate polymorphism as predisposal to aggressive traits.

Exploratory associations with tumor necrosis factor-α, disinhibition and suicidal endorsement after traumatic brain injury

PURPOSE

To examine the relationship of Tumor Necrosis Factor (TNF)-α to disinhibition and suicidal endorsement after traumatic brain injury (TBI).

PARTICIPANTS

Adults with moderate to severe TBI (acute serum levels: n=48, n=543 samples; acute CSF levels: n=37, n=389 samples; chronic serum levels: n=48, n=326 samples).

MAIN MEASURES

TNFα levels (CSF, Serum) from time of injury to 12 months post-injury; Frontal Systems Behavior Scale - Disinhibition Subscale at 6 and 12 months post-injury; Patient Health Questionnaire at 6 and 12 months post-injury.

RESULTS

Participants with TBI had significantly higher CSF and serum TNFα levels than healthy controls (p<0.05). Acute and chronic serum TNFα was significantly associated with disinhibition at 6 months post-injury (p=0.009, p=0.029 respectively), and 6 month disinhibition was associated with suicidal endorsement at both 6 and 12 months (p=0.045, p=0.033 respectively) and disinhibition at 12 months post-injury (p<0.001).

CONCLUSION

These preliminary data suggest a biological to behavioral pathway of suicidality after TBI, from TNFα to disinhibition to suicidal endorsement. Future investigation is warranted to validate these findings and clarify what biological mechanisms might underlie these relationships.

Serotonergic genes and suicide: a systematic review

Suicide is one of the leading causes of death in the world. Its aetiology is complex and diverse, however, epidemiological studies show that suicidal behavior is partly heritable. Neurobiological evidence implicates serotonergic dysfunction in suicidality, stimulating genetic research to focus on genes related to the serotonergic system. In this paper, we review evidence from studies examining the association between various serotonergic genes (Tryptophan Hydroxylase genes: TPH1; TPH2, Serotonin Transporter gene: 5-HTTLPR in SLC6A4, Serotonin Receptor genes: HTR1A, HTR2A, HTR1B, HTR2C and Monoamine Oxidase A gene: MAOA) and suicidal behavior. The data show associations between variation on the TPH1 gene and 5-HTTLPR gene and violent suicidal behavior in Caucasian populations, with the least inconsistencies. Results are mixed for the TPH2 gene and serotonin receptor genes, but for some genes, studies that include haplotypic analyses or that examine a larger coding region of the genes tend to provide more reliable results. Findings on endophenotypes of suicidality, such as aggression and impulsivity traits, show positive associations for the TPH1, HTR2A, and MAOA genes, but need further replication, since negative associations are also occasionally reported. Since genes can only partially explain suicidal risk, several studies during the past decade have tried to incorporate environmental factors in the susceptibility model. Studies to date show that variation on the 5-HTTLPR, MAOA and HTR2A gene can interact with stressful life events to increase risk for suicidal behavior. Limitations of case-control studies are discussed and future considerations are put forward with regard to endophenotypic measurements and gene-environment interactions.

Family-based study of HTR2A in suicide attempts: observed gene, gene × environment and parent-of-origin associations

While suicidal behavior is frequently accompanied by serotonergic system alterations, specific associations with genetic variation in the serotonin 2A receptor (HTR2A) gene have been inconsistent. Using a family-based study design of 660 offspring who have made a suicide attempt (SA) and both parents, we conducted an association and linkage analysis using single-nucleotide polymorphisms (SNPs) with extensive gene coverage, and included the study of parent-of-origin (POE) and gene-environment interaction (G × E), also using previously unstudied exposures. The main finding was a G × E between the exon 1 SNP rs6313 and exposure to cumulative types of lifetime stressful life events (SLEs), driven by overtransmission of CT and undertransmission of TT, both in relation to other genotypes. Further exploratory analysis revealed a significant POE in this G × E in female subjects, which followed a polar overdominant inheritance pattern. In addition, rs6310 and rs6305 were found to significantly associate with SA in the total sample. A G × E in female subjects (rs7322347 × physical assault in childhood/adolescence) confirmed features of a previously observed association with SA. Other potentially interesting nominally significant findings were observed, but like the G × E of rs7322347 did not pass a false-discovery rate cutoff. Taken together, this study found multiple associations of HTR2A SNPs on SA, with strongest statistical evidence for a G × E involving rs6313, and further suggested the importance of taking into account different inheritance patterns and G × Es with regard to HTR2A.

Association of the 5HTR2A gene with suicidal behavior: case-control study and updated meta-analysis

BACKGROUND

The polymorphism rs6313 (T102C) has been associated with suicidal behavior in case-control and meta-analysis studies, but results and conclusions remain controversial. The aim of the present study was to examine the association between T102C with suicidal behavior in a case-control study and, to assess the combined evidence - this case-control study and available data from other related studies - we carried out a meta-analysis.

METHODS

We conducted a case-control study that included 161 patients with suicide attempts and 244 controls; we then performed a meta-analysis. The following models were evaluated in the meta-analysis: A) C allele vs T allele; B) T allele vs C allele; C) Caucasian population, D) Asian population, and E) suicide attempters with schizophrenia.

RESULTS

We found an association between attempted suicide and control participants for genotype (χ2=6.28, p=0.04, df=2) and allele (χ2=6.17, p=0.01, df=1, OR 1.48 95% IC: 1.08-2.03) frequencies in the case-control study. The meta-analysis, comprising 23 association studies (including the present one), showed that the rs6313 polymorphism is not associated with suicidal behavior for the following comparisons:T allele vs C allele (OR: 1.03; 95% CI 0.93-1.13; p(Z)=0.44); C allele vs T allele: (OR:0.99; 95% CI: 0.90-1.08; p(Z)=0.22); Caucasians (OR:1.09; 95% CI: 0.96-1.23), and Asians (OR:0.96; 95% CI: 0.84-1.09).

CONCLUSION

Our results showed association between the rs6313 (T102C) polymorphism and suicidal behavior in the case-control study. However, the meta-analysis showed no evidence of association. Therefore, more studies are necessary to determine conclusively an association between T102C and suicidal behavior.