Suicide neurobiology

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.

Chronic pain in adolescents is associated with suicidal thoughts and behaviors

Adults who suffer from chronic pain are at increased risk for suicide ideation and attempts, but it is not clear whether adolescents with chronic pain are similarly at elevated risk. This study investigates whether chronic pain is associated with an increase in suicidal ideation/attempts independent of depression in a population sample of adolescents. We analyzed data from the National Longitudinal Study of Adolescent Health, a longitudinal study of a nationally representative sample of adolescents in the United States (N = 9,970). Most chronic pain was related to suicide ideation/attempt both in the last year (odds ratio [OR] 1.3-2.1) and during the subsequent year (OR 1.2-1.8). After controlling for depressive symptoms, headaches (OR = 1.3 last year, OR = 1.2 subsequent year) and muscle aches (OR = 1.3 last year) remained associated with suicide ideation but not suicide attempt. These findings show that chronic pain in adolescence is a risk factor for suicide ideation; this effect is partly but not fully explained by depression. Youth with comorbid depression and chronic pain are at increased risk of thinking about and attempting suicide. Clinicians should be alert to suicide ideation/attempt and comorbid depression in this at-risk population.

PERSPECTIVE

Adolescents who suffer from chronic pain are at increased risk for suicide ideation and attempt. Depressive symptoms account for the link between chronic pain and suicide attempt, but do not completely explain why adolescents with chronic pain show suicide ideation.

Dysfunction of astrocyte connexins 30 and 43 in dorsal lateral prefrontal cortex of suicide completers

BACKGROUND

Suicide is an important public health problem that results from the interaction of both psychosocial and biological factors. Although it is known that particular neurobiological processes underlie suicidal ideation and behavior, there still remains limited knowledge about the specific factors involved.

METHODS

To explore the neurobiology of suicide we generated microarray data from dorsal lateral prefrontal cortex (DLPFC) in each of 28 male French-Canadian subjects (20 suicide completers). These results were followed up in a larger French-Canadian sample (n = 47, 38 suicide completers) and in microarray data available from the Stanley Foundation (n = 100, 36 suicide completers). To investigate the molecular mechanisms of this finding, we performed RNA interference and electrophoretic mobility shift assays. Animal behavioral experiments were done to control for drug and alcohol effects.

RESULTS

We found reduced expression of Cx30 and Cx43 in DLPFC of suicide completers. We identified a previously unknown function for Sox9 as a transcription factor affecting expression of Cx30 in brain.

CONCLUSIONS

These results suggest that alterations of astrocyte connexins might be involved in the suicide process and provide further evidence implicating astrocytes in psychopathology.

Lethal forethought: delayed reward discounting differentiates high- and low-lethality suicide attempts in old age

BACKGROUND

The decision to commit suicide may be impulsive, but lethal suicidal acts often involve planning and forethought. People who attempt suicide make disadvantageous decisions in other contexts, but nothing is known about the way they decide about the future. Can the willingness to postpone future gratification differentiate between individuals prone to serious, premeditated and less serious, unplanned suicidal acts?

METHODS

Four groups of depressed participants aged 60 and older made choices between smaller immediate and larger delayed monetary rewards: 15 who had made high-lethality suicide attempts, 14 who had made low-lethality suicide attempts, 12 who seriously contemplated suicide, and 42 people with depression, but no history of suicidal thoughts. The reference group was 31 psychiatrically healthy elders.

RESULTS

Individuals who had made low-lethality attempts displayed an exaggerated preference for immediate rewards compared with nonsuicidal depressed and healthy control subjects. Those who had carried out high-lethality suicide attempts were more willing to delay future rewards, compared with low-lethality attempters. Better planned suicide attempts were also associated with willingness to wait for larger rewards. These effects were unchanged after accounting for education, global cognitive function, substance use disorders, psychotropic medications, and possible brain injury from attempts. Discount rates were correlated with having debt, but were not significantly associated with income, hopelessness, depressive severity, premorbid IQ, age at first attempt, or choice of violent means.

CONCLUSIONS

Although clinicians often focus on impulsivity in patients at risk for suicide, these data suggest that identifying biological characteristics and treatments for nonimpulsive suicidal older people may be even more important.

The possible contributory role of the S allele of 5-HTTLPR in the emergence of suicidality

Suicide is a complex and challenging human phenomenon, and, although knowledge is expanding concerning its risk factors, its background is still not fully understood. There is currently an increasing interest in genetic factors associated with suicide, since these may lead to the emergence of personality traits and temperaments that may be long-term predictors of suicidal behaviour. One of the most likely genetic candidates in the background of suicide is the 5-HTTLPR polymorphism of the serotonin transporter gene. This review focused on papers published on the association of the 5-HTTLPR polymorphism of the serotonin transporter gene and suicidal behaviour as well as research on possible endophenotypes related to suicide. Although there are contradictory results, several studies and meta-analyses support the idea that the S allele plays a role in the background of violent suicide. However, in order to be able to delineate the genetic background of suicide, different types of suicidal behaviour should be distinguished, since studies indicate that these may have different genetic factors. Also, personality traits and temperaments should be identified that may play a modulating role between genetic factors and suicidal behaviour. So far, neuroticism, affective temperaments, and impulsive aggression have been found to be associated with both the S allele and suicidal behaviour. This study aimed to integrate findings concerning possible endophenotypes modulating between genetic factors and manifested suicidal behaviour.

Risk and protective genetic variants in suicidal behaviour: association with SLC1A2, SLC1A3, 5-HTR1B &NTRK2 polymorphisms

Background

Suicidal behaviour is known to aggregate in families. Patients with psychiatric disorders are at higher risk for suicide attempts (SA), however protective and risk genetic variants for suicide appear to be independent of underlying psychiatric disorders. Here we investigate genetic variants in genes important for neurobiological pathways linked to suicidal behaviour and/or associated endophenotypes, for association with SA among patients with co-existing psychiatric illness. Selected gene-gene and gene-environment interactions were also tested.

Methods

DNA was obtained from bloods of 159 patients (76 suicide attempters and 83 non-attempters), who were profiled for DSM-IV Axis I psychiatric diagnosis. Twenty-eight single nucleotide polymorphisms (SNPs) from 18 candidate genes (COMT, 5-HT2A, 5-HT1A, 5-HTR1B, TPH1, MAO-A, TPH2, DBH, CNR1, BDNF, ABCG1, GABRA5, GABRG2, GABRB2, SLC1A2, SLC1A3, NTRK2, CRHR1) were genotyped. Genotyping was performed by KBioscience. Tests of association between genetic variants and SA were conducted using Chi squared and Armitage Trend tests. Binary logistical regression analyses were performed to evaluate the contribution of individual genetic variants to the prediction of SA, and to examine SNPs for potential gene-gene and gene-environment interactions.

Results

Our analysis identified 4 SNPs (rs4755404, rs2269272, rs6296 and rs1659400), which showed evidence of association with SA compared to a non-attempter control group. We provide evidence of a 3-locus gene-gene interaction, and a putative gene-environment interaction, whereby genetic variation at the NTRK2 locus may moderate the risk associated with history of childhood abuse.

Conclusion

Preliminary findings suggest that allelic variability in SLC1A2/3, 5-HTR1B and NTRK2 may be relevant to the underlying diathesis for suicidal acts.

Potential peripheral biological predictors of suicidal behavior in major depressive disorder

Previous studies have shown that dysfunctions in the serotonin system and hypothalamic-pituitary-adrenal axis (HPA) are associated strongly with suicidal behavior and suicide, especially among individuals with major depressive disorder. Suicidal behavior has been explained using both the stress-diathesis model and the state-trait interaction model. Specifically, diatheses, or trait-dependent risk factors, are associated with dysfunctions in the serotonin system; however, stress responses, or state-dependent factors, are associated with HPA hyperactivity. Decreases in cholesterol and brain-derived neurotrophic factor (BDNF) levels have been associated with impaired brain plasticity among individuals with suicidal behavior. Decreased serotonin functioning has been measured using cerebral spinal fluid (CSF) 5-HIAA, fenfluramine challenge studies, and platelet 5-HT2A receptors. HPA axis dysfunction has been evaluated with the dexamethasone suppression test. Cholesterol and BDNF levels have been measured in blood serum or plasma. Nevertheless, challenges to finding promising and accessible neurobiological predictors of suicide and suicidal behavior remain. As suicide behavior is a complex phenomenon, a combined or multidimensional approach, including each of the aforementioned methods, may be required to predict suicide risk among individuals with major depressive disorder.

Global gene expression profiling of the polyamine system in suicide completers

In recent years, gene expression, genetic association, and metabolic studies have implicated the polyamine system in psychiatric conditions, including suicide. Given the extensive regulation of genes involved in polyamine metabolism, as well as their interconnections with the metabolism of other amino acids, we were interested in further investigating the expression of polyamine-related genes across the brain in order to obtain a more comprehensive view of the dysregulation of this system in suicide. To this end, we examined the expression of genes related to polyamine metabolism across 22 brain regions in a sample of 29 mood-disordered suicide completers and 16 controls, and identified 14 genes displaying differential expression. Among these, altered expression of spermidine/spermine N1-acetyltransferase, spermine oxidase, and spermine synthase, has previously been observed in brains of suicide completers, while the remainder of the genes represent novel findings. In addition to genes with direct involvement in polyamine metabolism, including S-adenosylmethionine decarboxylase, ornithine decarboxylase antizymes 1 and 2, and arginase II, we identified altered expression of several more distally related genes, including aldehyde dehydrogenase 3 family, member A2, brain creatine kinase, mitochondrial creatine kinase 1, glycine amidinotransferase, glutamic-oxaloacetic transaminase 1, and arginyl-tRNA synthetase-like. Many of these genes displayed altered expression across several brain regions, strongly implying that dysregulated polyamine metabolism is a widespread phenomenon in the brains of suicide completers. This study provides a broader view of the nature and extent of the dysregulation of the polyamine system in suicide, and highlights the importance of this system in the neurobiology of suicide.

Animal model and neurobiology of suicide

Animal models are formidable tools to investigate the etiology, the course and the potential treatment of an illness. No convincing animal model of suicide has been produced to date, and despite the intensive study of thousands of animal species naturalists have not identified suicide in nonhuman species in field situations. When modeling suicidal behavior in the animal, the greatest challenge is reproducing the role of will and intention in suicide mechanics. To overcome this limitation, current investigations on animals focus on every single step leading to suicide in humans. The most promising endophenotypes worth investigating in animals are the cortisol social-stress response and the aggression/impulsivity trait, involving the serotonergic system. Astroglia, neurotrophic factors and neurotrophins are implied in suicide, too. The prevention of suicide rests on the identification and treatment of every element increasing the risk.

Association study of EP1 gene polymorphisms with suicide completers in the Japanese population

BACKGROUND

Both environmental and genetic factors have been reported to be involved in suicidal behaviors. Considerable evidence indicates that impulsive aggression is one of the important risk factors that contribute to suicide. A recent study has shown that prostaglandin E2 type 1 receptor (EP1) signaling regulates impulsive-aggressive behaviors in mice under both social and environmental stresses. To test the possible involvement of the EP1 gene in suicide, we carried out an association study of EP1 gene polymorphisms with suicide completers in the Japanese population.

METHODS

We studied 5 SNPs including one SNP in exon 2 (rs3745459) and four SNPs in the potential promoter region of the EP1 gene (rs3810255, rs3810254, rs3810253 and rs10416814) in 374 healthy control and 287 completed suicide victims using standard Taqman probe genotyping assays.

RESULTS

No significant differences of the genotypic distribution, allelic frequency or haplotype distribution between controls and suicide completers were found. Gender based analysis revealed that genotypic, allelic and haplotypic distributions of rs3810255, rs3810254, rs3810253 and rs10416814 SNPs were significantly different between the female control and female suicide groups, although the differences did not withstand correction for multiple comparisons.

CONCLUSION

We could not find an association of EP1 gene with suicide in the Japanese population. Because several SNPs in the promoter region of the EP1 gene were nominally significantly associated with suicide in the female, further studies with a larger sample size and different population are needed to confirm this result.

New perspectives in glutamate and anxiety

Anxiety and stress-related disorders, namely posttraumatic stress disorder (PTSD), generalized anxiety disorder (GAD), obsessive-compulsive disorder (ODC), social and specific phobias, and panic disorder, are a major public health issue. A growing body of evidence suggests that glutamatergic neurotransmission may be involved in the biological mechanisms underlying stress response and anxiety-related disorders. The glutamatergic system mediates the acquisition and extinction of fear-conditioning. Thus, new drugs targeting glutamatergic neurotransmission may be promising candidates for new pharmacological treatments. In particular, N-methyl-d-aspartate receptors (NMDAR) antagonists (AP5, AP7, CGP37849, CGP39551, LY235959, NPC17742, and MK-801), NMDAR partial agonists (DCS, ACPC), α-amino-3-hydroxyl-5-methyl-4-isoxazole-propionate receptors (AMPARs) antagonists (topiramate), and several allosteric modulators targeting metabotropic glutamate receptors (mGluRs) mGluR1, mGluR2/3, and mGluR5, have shown anxiolytic-like effects in several animal and human studies. Several studies have suggested that polyamines (agmatine, putrescine, spermidine, and spermine) may be involved in the neurobiological mechanisms underlying stress-response and anxiety-related disorders. This could mainly be attributed to their ability to modulate ionotropic glutamate receptors, especially NR2B subunits. The aim of this review is to establish that glutamate neurotransmission and polyaminergic system play a fundamental role in the onset of anxiety-related disorders. This may open the way for new drugs that may help to treat these conditions.

Tobacco consumption and antidepressant use are associated with the rate of completed suicide in Hungary: an ecological study

The suicide rate of Hungary is the highest in the world averaged over the last century but it has shown a very pronounced decrease since 1987. To explore the background of this decrease we investigated the associations between some known suicide-related factors (i.e. tobacco use, antidepressant use and alcohol consumption at the population level) and the suicide rate between 1985 and 2008. The total number of man-hours worked per year by psychiatrists in the outpatient service system and real GDP growth were also monitored in our study. A time series analysis model was constructed to investigate the associations between the above variables and the suicide rate. In the unadjusted model annual tobacco consumption was significantly associated with the suicide rate in a positive manner, while antidepressant use and man-hours were significantly associated with the suicide rate in a negative manner. After adjustment, the associations remained significant only for tobacco consumption and antidepressant use. Neither alcohol consumption nor real GDP growth was associated with the suicide rate in any models. Our results from group-level data confirmed the role of smoking in suicidal behavior previously suggested mainly by studies using individual-level data and also corroborated the results of previous ecological studies concerning the inverse association between antidepressant use and suicide rate. These findings and the results of previous studies - investigating the relationship between smoking and the risk of suicidal behavior at the individual-level - may suggest that programs to prevent tobacco use or to address the widespread recognition and treatment of depression may also prevent suicidality.

Association of FKBP5 gene haplotypes with completed suicide in the Japanese population

BACKGROUND

The hypothalamus-pituitary-adrenal (HPA) axis is known to have a role in suicidal behaviors in patients with affective disorders. However, the incomplete overlapping of the genetic factors of suicidal behaviors and the genetic factors of affective disorders suggest that the genes associated with predisposition to suicidal behaviors and affective disorders are different. There is increasing evidence that genes regulating the HPA axis have effects on suicidal behaviors. To test this idea, we examined the association of three HPA axis-related genes (glucocorticoid receptor (NR3C1), mineralocorticoid receptors (NR3C2), and FK506 binding protein 5 (FKBP5)) with suicide.

METHODS

We selected 3 SNPs of the FKBP5 (rs3800373, rs1360780, and rs2395635), 2 SNPs of the NR3C1 (rs6196 and rs10052957), and 3 SNPs of the NR3C2 genes (rs5525, rs5522, and rs2070951) based on their frequency in the Japanese population. Using TaqMan probe assays, we determined these SNPs in 219 completed suicide victims and 228 age- and gender-matched healthy control subjects.

RESULTS

No significant differences in genotypic distribution or allelic frequency of any single SNPs between the completed suicide and control groups were observed. The distributions of TT, TC, and GT haplotypes of the FKBP5 gene (comprised of rs3800373 and rs1360780) between the completed suicide and control groups were significantly different (p<0.05 for each haplotype). The TC haplotype withstood correction for multiple comparisons (corrected p = 0.034).

CONCLUSION

Our results suggest that haplotypes in FKBP5 gene are associated with completed suicide. This finding needs to be confirmed using rigorous SNPs selection in a larger sample.

Increased cortical expression of an RNA editing enzyme occurs in major depressive suicide victims

RNA editing is a posttranscriptional process which critically modulates the function of several neurotransmitter receptors regulating mood, anxiety, learning, and memory. Data from several postmortem studies have shown increased 5-hydroxytryptamine-2C receptor RNA editing in mood disorders and suicide, and therefore the 5-hydroxytryptamine-2C receptor might be expected to have reduced signal transduction in these patients. In this study, we have tested the hypothesis that the expression levels of the enzymes which catalyze RNA editing, adenosine deaminase acting on RNA 1 (ADAR1) and ADAR2, are also abnormal in suicide. Gene expression was measured in the dorsolateral prefrontal cortex of individuals from the Stanley Consortium Brain series, which includes patients with schizophrenia (n=15), major depression (n=15), bipolar disorder (n=15), and a comparison group (n=14). Of the psychiatric patients, 20 were suicide victims. ADAR1 expression was found to be significantly increased in major depressive suicide victims compared with patients who did not commit suicide. Neither ADAR1 nor ADAR2 expression was altered in any of the other diagnostic groups. These data indicate that ADAR1 could play a role in the pathophysiology of suicide in patients with major depression.

Pharmacogenomics of suicidal events

Pharmacogenomic studies of antidepressant treatment-emergent suicidal events in depressed patients report associations with polymorphisms in genes involved in transcription (CREB1), neuroprotection (BDNF and NTRK2), glutamatergic and noradrenergic neurotransmission (GRIA3, GRIK2 and ADRA2A), the stress and inflammatory responses (FKBP5 and IL28RA), and the synthesis of glycoproteins (PAPLN). Nearly all of the reported events in these studies were modest one-time increases in suicidal ideation. In 3231 unique subjects across six studies, 424 (13.1%) patients showed increases in suicidal ideation, eight (0.25%) attempted suicide and four (0.12%) completed suicide. Systems related to most of these genes have also been implicated in studies of suicidal behavior irrespective of treatment. Future pharmacogenomic studies should target events that are clinically significant, related clinical phenotypes of response and medication side effects, and biological pathways that are involved in these outcomes in order to improve treatment approaches.

Mixture regression analysis on age at onset in bipolar disorder patients: investigation of the role of serotonergic genes

Bipolar Disorder (BPD) is a complex psychiatric disease with a relevant underlying genetic basis. HTR2A T102C, HTR2C Cys23Ser, SLC6A4 5-HTTLPR and rs25531 polymorphisms were genotyped in 230 BPD patients and inserted as covariates in a mixture regression model of age at onset (AAO). 5-HTTLPR polymorphism associated with early onset component under recessive and additive model. HTR2A T102C, HTR2C Cys23Ser and 5-HTTLPR interaction terms associated with early onset component under dominant, recessive and additive model. These findings suggest a role of genes codifying for elements of the serotonergic system in influencing the AAO in BPD.

A common polymorphism in the 3'-UTR of the NOS1 gene was associated with completed suicides in Japanese male population

BACKGROUND

Suicidal behavior has been widely accepted as familial. Its transmission cannot be explained by the transmission of psychiatric disorder alone and seems to be partly explained by the transmission of impulsive-aggressive behavior. Studies in laboratory animal have shown that mice lacking NOS1 manifest significant aggressive behavior. Further, several polymorphisms of neuronal nitric oxide synthase (NOS1) gene have been reported to be associated with impulsivity, aggression and suicide attempts. To further clarify the possible involvement of NOS1 with suicide, we carried out an association study of NOS1 gene polymorphisms with completed suicide.

METHODS

We examined 7 single nucleotide polymorphisms (SNPs) of the NOS1 gene which were previously studied in several neuropsychiatric disorders (rs2682826, rs6490121, rs3782206, rs561712, rs3782219, rs3782221, and rs41279104), in age and gender matched 287 healthy control subjects and 284 completed suicides using the TaqMan probe assays.

RESULTS

We found that both the genotypic distribution and the allelic frequencies of rs2682826 SNP were significantly different between the completed suicide and control groups (P=0.0007 and 0.0005, respectively). The odd ratio for the minor allele of the SNP was 0.653 (95% CI 0.513-0.832). The significance was remained even after correction for multiple testing. Gender-based analysis showed that the significances were appeared in males only.

CONCLUSION

Our study raises a possibility that a genetic variation of NOS1 may be implicated in the pathophysiology of suicide in Japanese population, especially in males. Further studies on more NOS1 genetic variants are needed to confirm our observations.