Tryptophan hydroxylase immunoreactivity is altered by the genetic variation in postmortem brain samples of both suicide victims and controls

Whole-brain structural and functional neuroimaging of individuals who attempted suicide and people who did not: A systematic review and exploratory coordinate-based meta-analysis

Suicide is the cause of death of approximately 800,000 people a year. Despite the relevance of this behaviour, risk assessment tools rely on clinician experience and subjective ratings. Given that previous suicide attempts are the single strongest predictors of future attempts, we designed a systematic review and coordinate-based meta-analysis to demonstrate whether neuroimaging features can help distinguish individuals who attempted suicide from subjects who did not. Out of 5,659 publications from PubMed, Scopus, and Web of Science, we summarised 102 experiments and meta-analysed 23 of them. A cluster in the right superior temporal gyrus, a region implicated in emotional processing, might be functionally hyperactive in individuals who attempted suicide. No statistically significant differences in brain morphometry were evidenced. Furthermore, we used JuSpace to show that this cluster is enriched in 5-HT1A heteroreceptors in the general population. This exploratory meta-analysis provides a putative neural substrate linked to previous suicide attempts. Heterogeneity in the analytical techniques and weak or absent power analysis of the studies included in this review currently limit the applicability of the findings, the replication of which should be prioritised.

Tryptophan Hydroxylase 1 Variant rs1800532 is Associated with Suicide Attempt in Serbian Psychiatric Patients but does not Moderate the Effect of Recent Stressful Life Events

Tryptophan hydroxylase 1 (TPH1) gene, coding for serotonin synthesizing enzyme, and recent stressful life events (SLEs) have been commonly associated with suicidal behavior. TPH1 has been also hypothesized to be involved in stress-response mechanisms. The aim of this study was to assess TPH1 variant rs1800532 and its possible interaction with recent SLEs as risk factors for suicide attempt (SA) in Serbian psychiatric patients, including 165 suicide attempters and 188 suicide nonattempters. rs1800532 and recent SLEs were independently associated with SA, while rs1800532 did not moderate the effect of recent SLEs on SA vulnerability among Serbian psychiatric patients.

The neurobiology of suicide - A Review of post-mortem studies

The neurobiology of suicidal behaviour, which constitutes one of the most serious problems both in psychiatry and general medical practice, still remains to a large degree unclear. As a result, scientists constantly look for new opportunities of explaining the causes underlying suicidality. In order to elucidate the biological changes occurring in the brains of the suicide victims, studies based on post-mortem brain tissue samples are increasingly being used. These studies employ different research methods to provide an insight into abnormalities in brain functioning on various levels, including gene and protein expression, neuroplasticity and neurotransmission, as well as many other areas. The aim of this paper to summarize the available data on the post-mortem studies, to provide an overview of main research directions and the most up-to-date findings, and to indicate the possibilities of further research in this field.

Serotonin receptor, SERT mRNA and correlations with symptoms in males with alcohol dependence and suicide

OBJECTIVE

This study tested the hypothesis that abnormalities in components of the serotonin (5HT) system in the prefrontal cortex are associated with suicide in alcohol-dependent subjects. Second, we assessed the relationship of lifetime impulsivity and mood symptoms with prefrontal cortex 5-HT measures.

METHOD

Tissue was obtained from Brodmann's areas (BA) 9 and 24 in postmortem samples of individuals who were alcohol dependent with suicide (n = 5), alcohol dependent without suicide (n = 9) and normal controls (n = 5). Serotonin receptor (5HT) and serotonin reuptake transporter (SERT) mRNA were measured. Interviews with next of kin estimated lifetime impulsivity and mood symptoms in the last week of life.

RESULTS

Serotonin receptor 1A (5HT1A) mRNA in BA 9 was elevated in the alcohol dependence without suicide group compared with controls. In the alcohol dependence with suicide group, anxiety symptoms were associated with decreased BA 24 SERT mRNA and depressive symptoms with BA 9 5HT1A mRNA expression. In the alcohol dependent only group impulsivity is correlated with increased BA 9, and BA 24 serotonin receptor 2A mRNA.

CONCLUSION

Our data suggest region-specific change, rather than global serotonin blunting is involved in alcohol dependence and suicide. It also suggests that symptoms are differentially influenced by prefrontal cortex serotonin receptor mRNA levels.

Tryptophan hydroxylase gene 1 (TPH1) variants associated with cerebrospinal fluid 5-hydroxyindole acetic acid and homovanillic acid concentrations in healthy volunteers

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin synthesis. We investigated possible relationships between five TPH1 gene polymorphisms and cerebrospinal fluid (CSF) concentrations of the major serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), the major dopamine metabolite homovanillic acid (HVA), and the major norepinephrine metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy volunteers (n=132). The G-allele of the TPH1 rs4537731 (A-6526G) polymorphism was associated with 5-HIAA and HVA, but not MHPG concentrations. None of the other four TPH1 polymorphisms (rs211105, rs1800532, rs1799913 and rs7933505) were significantly associated with any of the monoamine metabolite concentrations. Two (rs4537731G/rs211105T/rs1800532C/rs1799913C/rs7933505G and rs4537731A/rs211105T/rs1800532C/rs1799913C/rs7933505G) of five common TPH1 five-allele haplotypes were associated with 5-HIAA and HVA concentrations in opposite directions. None of the common haplotypes was associated with MHPG concentrations in the CSF. The results suggest that TPH1 gene variation participates in the regulation of serotonin and dopamine turnover rates in the central nervous system of healthy human subjects.

Risk-taking behavior in a gambling task associated with variations in the tryptophan hydroxylase 2 gene: relevance to psychiatric disorders

Decision making, choosing the best option from the possible outcomes, is impaired in many psychiatric conditions including affective disorders. We tested the hypothesis that variations in serotonergic genes (TPH2, TPH1, SLC6A4, HTR1A), which influence serotonin availability, affect choice behavior in a probabilistic gambling task. A population cohort (N=1035) completed a paper-and-pencil gambling task, filled out personality and symptom questionnaires and gave consent for the use of their DNA in a genetic association study. A subgroup of subjects (N=69) also completed a computer version of the task. The gambling task was designed to estimate an individual's tendency to take a risk when choosing between a smaller but more certain 'win' and a larger, less probable one. We genotyped seven haplotype tagging SNPs in the TPH2 gene, and previously reported functional polymorphisms from the other genes (rs1800532, 5HTTLPR, and rs6295). Carriers of the more prevalent TPH2 haplotype, which was previously associated with less active enzyme variant, showed reduced risk taking on both tasks compared with subjects not carrying the common haplotype. The effect of TPH2 haplotypes on risk-taking was independent of current depression and anxiety symptoms, neuroticism and impulsiveness scores. We did not find an association between functional polymorphisms in the TPH1, SLC6A4, HTR1A genes and risk-taking behavior. In conclusion, our study demonstrates the role of the TPH2 gene and the serotonin system in risk taking and suggests that TPH2 gene may contribute to the expression of psychiatric phenotypes through altered decision making.

Neuronal tryptophan hydroxylase (TPH2) in suicidal behaviour

Serotonin (5-hydroxytryptamine, 5-HT) is a signalling molecule involved in many brain functions as well as in a variety of psychiatric conditions, including suicidal behaviour. Tryptophan hydroxylase (TPH), the rate-limiting enzyme of 5-HT biosynthesis, plays a critical role in 5-HT metabolism and thus in the regulation of 5-HT neurotransmission. There are two isoforms of TPH, so-called peripheral (TPH1) and neuronal (TPH2), encoded by the two distinct genes. TPH1 is abundant in the peripheral tissues, while TPH2 was detected exclusively within the nervous system. Since its discovery in 2003, TPH2 gene has attracted great interest as a potential factor contributing to diathesis of suicidal behaviour. However, initial positive findings indicating an association of TPH2 genetic variants with suicide have not been replicated consistently. Here we provide an overview of published studies to date, that have evaluated the contribution of TPH2 gene to the etiopathogenesis of suicidal behaviour.

An Association Study of the A218C Polymorphism of the Tryptophan Hydroxylase 1 Gene with Eating Disorders in a Korean Population: A Pilot Study

OBJECTIVE

We examined the association between the tryptophan hydroxylase 1 (TPH1) gene and eating disorders focusing on obsessionality.

METHODS

The sample included 62 women with a lifetime diagnosis of anorexia nervosa (AN) as well as 50 women with a lifetime diagnosis of bulimia nervosa (BN) recruited from specialist clinics for eating disorders and 131 healthy women in Korea. Blood samples were collected from all participants for the TPH1 genotyping. The patients were ad ministered the Korean version of the Eating Disorders Examination and obsessionality was conceptualized using measures of persistence, harm avoidance, and obsessive-compulsive symptoms.

RESULTS

In the case-control comparisons, the frequency of the A/A genotype was increased in the patients with BN, but this difference was not significant after correcting for multiple testing. We found no effect of the TPH A218C polymorphism on obsessionality in the patients with AN or BN.

CONCLUSION

Although the present findings should be regarded as preliminary because of the small size of our sample, they suggest that the TPH1 gene may contribute to the genetic susceptibility to BN and be associated with the other unexplored traits of bulimic case status.

Association between serotonin-related gene polymorphisms and suicidal behavior in depressive patients

BACKGROUND

Several studies have suggested that there is a substantial genetic contribution to suicidal behavior. Genes encoding proteins involved in serotonergic transmission are major candidates in association studies of suicidal behavior. In this study, we aimed to investigate the 5-HT2A receptor (5HTR2A) and tryptophan hydroxylase (TPH) genes for association with suicidal behavior in depressive patients.

METHODS

Patients with major depression who had recently attempted suicide (n=191) and control subjects (n=193) were genotyped for 5HTR2A 102T/C, and TPH 218A/C. The lethality of the suicide attempt was measured using the Risk-Rescue Rating (RRR) and Lethality Suicide Attempt Rating Scale (LSARS). The severity of depression was measured using the Hamilton Depression Rating Scale (HDRS).

RESULTS

There were no significant differences in the genotype distributions or allelic frequencies in the two serotonergic polymorphisms between suicide attempters and normal controls. None of the two serotonergic polymorphisms was correlated with lethality.

CONCLUSIONS

We concluded that these polymorphisms may not be associated with susceptibility to suicidal behavior in our Korean population. Our results were in line with most previous studies. More work is needed to replicate these findings. Our future studies aim at identifying other genetic associations.

Association of RGS2 gene polymorphisms with suicide and increased RGS2 immunoreactivity in the postmortem brain of suicide victims

Regulators of G-protein signaling are a family of proteins that negatively regulate the intracellular signaling of G protein-coupled receptors, such as the serotonin receptor. Recent studies have suggested that one of these proteins, the regulator of G-protein signaling 2 (RGS2), plays an important part in anxiety and/or aggressive behavior. To explore the involvement of the RGS2 gene in the vulnerability to suicide, we screened Japanese suicide victims for sequence variations in the RGS2 gene and carried out an association study of RGS2 gene polymorphisms with suicide victims. In the eight identified polymorphisms that were identified by mutation screening, we genotyped four common single-nucleotide polymorphisms (SNPs) in the RGS2 gene, and found significant differences in the distribution of the SNP3 (C+2971G, rs4606) genotypes and alleles of the SNP2 (C-395G, rs2746072) and the SNP3 between completed suicides and the controls. The distribution of the haplotype was also significantly different between the two groups (global p<0.0001). Furthermore, RGS2 immunoreactivity significantly increased in the amygdala and the prefrontal cortex (Brodmann area 9 (BA9)) of the postmortem brain of the suicide subjects. These findings suggest that RGS2 is genetically involved in the biological susceptibility to suicide in the Japanese population.

Stress, genes and the biology of suicidal behavior

Suicidal behavior is partly heritable. Studies seeking the responsible candidate genes have examined genes involved in neurotransmitter systems shown to have altered function in suicide and attempted suicide. These neurotransmitter systems include the serotonergic, noradrenergic, and dopaminergic systems and the hypothalamic-pituitary-adrenal axis. With some exceptions, most notably the serotonin transporter gene promoter polymorphism (HTTLPR), replication of candidate gene association studies findings has been difficult. This article reviews current knowledge of specific gene effects and gene-environment interactions that influence risk for suicidal behavior. Effects of childhood stress on development and how it influences adult responses to current stress are shown to be relevant for mood disorders, aggressive/impulsive traits, and suicidal behavior.

No association between the TPH A218C polymorphism and personality traits in Japanese healthy subjects

It has been suggested that the central serotonergic activity is implicated in personality traits. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin synthesis. In the present study, the association between the TPH A218C polymorphism and personality traits assessed by the Temperament and Character Inventory (TCI) was examined in 345 Japanese healthy subjects. The TPH A218C polymorphism was determined by a PCR-RFLP method. There were no significant differences in the seven dimension scores of TCI among the A/A, A/C, and C/C genotype groups by the one-way ANOVA. There was a significant negative correlation between age and the NS scores. Females showed significantly higher scores of HA, RD, and ST, and significantly lower scores of SD than males. The multiple regression analysis using age, gender, and the TPH genotype as independent variables also showed no significant association between any dimension score and the genotype. The present study thus suggests that the TPH A218C polymorphism does not affect personality traits in Japanese healthy subjects.

Association of TPH1 with suicidal behaviour and psychiatric disorders in the Chinese population

Tryptophan hydroxylase (TPH), the rate limiting enzyme in serotonin biosynthesis, is one of the most important regulating factors in the serotonergic system. Recently, polymorphisms of the TPH gene have been identified as being associated with suicide, but the evidence is inconsistent. To investigate the role in suicide of one of the isoforms, TPH1, we examined the association of five single nucleotide polymorphisms (SNPs) in the promoter region and in intron 7 of the TPH1 gene based on a sample from the Chinese population of 810 subjects, of whom 329 had made no suicide attempts (NSA), 297 had made suicide attempts (SA), and 184 were healthy subjects (HS). In this study, we observed statistically significant differences between NSA and HS subjects in allele distributions on one marker, -6526A (p = 0.0329; odds ratio (OR) 1.36; 95% confidence interval (CI) 1.01 to 1.81). No significant difference in genotype distribution or allele frequencies of other polymorphisms was found between the suicide victims and the controls. The overall haplotype frequency was significantly different between cases and healthy controls (p = 0.000024 NSA v HS; p < 0.000001, SA v HS; p < 0.000001, cases v HS). We found the haplotype TCAAA of -7180/-7065/-6526/218/779 to be strongly associated with suicidal behaviour and psychiatric disorders (p = 0.00243; OR = 1.62; 95% CI 1.17 to 2.24 and p = 0.018; OR = 1.41; 95% CI 1.05 to 1.91), which suggests an association of TPH1 with suicidal behaviour and indicates that TPH1 may play a significant role in the aetiology of psychiatric disorders in the Han Chinese population.

Investigation of A218C tryptophan hydroxylase polymorphism: association with familial suicide behavior and proband's suicide attempt characteristics

According to WHO, suicide accounts for about 1,000,000 deaths worldwide every year. In view of these dramatic data, several studies have tried to identify possible biological mechanisms and markers of suicide. Genes encoding for proteins involved in the serotonergic transmission are major candidates in association studies of suicidal behavior. The gene that codes for tryptophan hydroxylase (TPH), the rate-limiting enzyme in the biosynthesis of serotonin, is one of these candidates. Two polymorphisms in intron 7 of this gene (A218C and A779C) have been described, but their role in suicidal behavior remains uncertain. TPH A218C polymorphism was analyzed in a sample of 248 psychiatric patients and 63 healthy controls. In addition, at least one close relative member was interviewed to assess family suicidal behavior history. Our research confirmed that a positive history of suicide attempts in a family member is associated with the chance of an individual to attempt suicide. Furthermore, we demonstrated that familial suicide attempts are more lethal and frequently more violent. We were not able to find significant differences of the TPH genotype frequencies between patients and controls. The TPH A218C genotypes were not associated with a history of suicide attempt and the lethality of the most lethal lifetime suicide attempt and suicide attempt method. The authors conclude that the A218C polymorphism of the TPH gene may not be a susceptibility factor for suicidal behavior in this group of psychiatric patients but confirm that a family suicidal behavior history increases the proband's suicide attempt risk.

Genetics of suicide

The concept that genetic factors contribute to the complex trait of suicidal behaviour has stimulated much work aimed at identifying susceptibility genes. So far molecular genetic studies focused on the serotonergic pathway as the intent to die and the lethality of suicide acts were related to the serotonergic system. Two genes have so far emerged as being involved in the vulnerability for suicidality: first, the intronic polymorphisms (A218C or A779C) of the tryptophan hydroxylase 1 (TPH1) gene, which was suggested as a quantitative risk factor for suicidal behaviour; second, the insertion/deletion polymorphism of the serotonin transporter gene (5-HTTLPR), which does not seem to be involved in general suicidal behaviour, but in violent and repeated suicide attempts. The data have further shown that the MAOA gene, which is consistently associated with impulsive-aggressive personality traits, is not related to suicide but might induce violent methods in subjects with other suicide risk factors. Predominantly negative were the findings with any type of the serotonin receptors and inconsistent with catecholamine-synthesizing and -metabolizing enzymes or with the dopaminergic receptors. This paper reviews the status of current knowledge in this area, points to the weakness of the investigations and presents new approaches beyond the serotonergic system.

TPH gene polymorphism and aging: indication of combined effect on the predisposition to violent suicide

Findings relating serotonin to suicidal behavior suggest the role of genes for tryptophan hydroxylase (TPH) in the genetic substrate of this disorder. Association of Tph1 gene and suicidality, despite considerable research efforts, remains controversial. Polymorphism A218C in intron 7 of Tph1 gene was studied in violent suicide victims (N = 247) and controls (N = 320) of Slavic (Croatian) origin, with specific consideration of the influence of subjects' age. The frequency of, allegedly less active, CC genotype was increased in older (above 65 years) victims as compared to controls (P = 0.0126 and 0.0008, for comparison with age-specific and integral control samples, respectively), while there were no differences between victims under 65 years and controls. Excess of the CC genotype in elderly victims of violent suicide points to the possible combined effect of the respective genetic factor and physiological changes during aging on the predisposition to this disorder.

Lack of an association between 5-HT receptor gene polymorphisms and suicide victims

An association between serotonergic dysfunction in the brain and suicidal behavior has previously been suggested. The high affinity of some antipsychotic and antidepressant drugs to serotonin 6 (5-HT6) receptors, and the predominant localization of 5-HT6 receptors in some limbic regions, suggest that 5-HT6 receptors play a role in the pathogenesis of suicide. The objective of the present study was to examine the association between suicide victims and two polymorphisms of the 5-HT6 receptor gene: a biallelic polymorphism (267C/T) in exon 1 and a trinucleotide repeat polymorphism ([GCC](2/3)) in the 5'-upstream region of the gene. The two polymorphisms were genotyped in 163 suicide victims and 166 controls, and the distribution of genotype and allele frequencies between the two groups were compared. Haplotype frequencies of these two polymorphisms were estimated from genotypic data by the maximum-likelihood method. In both polymorphisms, there were no significant differences in genotype or allele frequencies between the suicide victims and the controls. Moreover, there were no significant differences in the haplotype distributions of these polymorphisms between the two groups. These findings suggest that it is unlikely that the 5-HT6 receptor gene is involved in the susceptibility to suicide.

Association of 14-3-3 ε gene haplotype with completed suicide in Japanese

Genetic factors have been suggested to be involved in suicide. Although some genetic factors, such as serotonergic transduction, have been associated with suicide, the results are inconsistent. There is a possibility that various signaling anomalies are involved in the biological vulnerability to suicide. We carried out a genome-wide gene-expression study in the brains of suicide victims using DNA microarrays;14-3-3 epsilon, which is related to neurogenesis, was one of the genes upregulated in the brains of suicide victims in the microarray analysis. This was confirmed by Western blot analysis. To examine the possibility of the involvement of 14-3-3 epsilon in the pathogenesis of suicide, we investigated the association of the 14-3-3 epsilon gene and completed suicide. We used three high-frequency SNPs (rs1532976, rs3752826, and rs9393) and found a significant association of two alleles (rs1532976 and rs3752826) with completed suicide (p < 0.05). Moreover, the distribution of haplotype revealed a more significant difference between completed suicide and controls (p=0.0005). This finding suggests that 14-3-3 epsilon is a potential suicide susceptibility gene and implies that dysregulation of neurogenesis may be involved in suicide.

Variability of the tryptophan hydroxylase gene: study in victims of violent suicide

Tryptophan hydroxylase (TPH), the enzyme controlling serotonin synthesis, is considered to be a potential contributor to the biological substrate of suicide. The association of the promoter (-7065CT) and intron 7 (218AC) polymorphisms, and the related haplotype, of the Tph1 gene with suicidal behavior was investigated in a sample of 160 victims of violent suicide and 284 healthy controls. All individuals were males of Croatian (Slavic) origin. Allele frequencies of both polymorphisms in Croatian controls were similar to control values reported for other European populations. Alleles at the two loci demonstrated highly significant linkage disequilibrium. No differences between controls and victims for the Tph1 genetic variation, either at single loci, or at a haplotypic level, were demonstrated, albeit there was a tendency, not reaching statistical significance, towards an increase of the intron 7CC genotype in the suicide group. Negative association results on the individual Tph1 loci, in accordance with the majority of previous reports, confirmed the lack of their major effect also in the Slavic ethnicity. Haplotypic results, on the other hand, opposing the previous positive finding, point to the possible influence of ethnicity (or gender) on the association between the Tph1 gene polymorphism and suicide.

Regional mRNA expression of a second tryptophan hydroxylase isoform in postmortem tissue samples of two human brains

Tryptophan hydroxylase (TPH) as rate limiting enzyme in the biosynthesis of serotonin plays a major role as candidate gene in several psychiatric disorders. Recently a second TPH isoform (TPH2) was identified in mice, which was exclusively expressed in the brain. We investigated whether the mRNA of the human homologue of this new TPH2 isoform is expressed in the human brain but not in peripheral tissues. The study was performed with postmortem specimen obtained from two subjects who died on cardiovascular failure. TPH2 mRNA levels were determined by quantitative real time RT-PCR. TPH2 mRNA was exclusively present in the human brains but not in the investigated peripheral tissues. Our finding may open up new research strategies for the analysis of the repeatedly observed disturbances in the serotonergic system in patients suffering from several psychiatric disorders.

Genes associated with addiction: alcoholism, opiate, and cocaine addiction

Drug addiction is a complex disorder that has a large spectrum of causes. Vulnerability to addiction has been shown in twin studies to have a robust genetic component. This genetic basis for addiction has general and specific components for each drug abused. Although many genes have been implicated in drug addiction, only a handful have either been replicated to have an association or to have an identified functional mechanism related to specific effects of abused drugs. A few selected genetic variants that currently look promising for the study of alcohol, opiate, and cocaine addiction are discussed in this article.

Genetics of the serotonergic system in suicidal behavior

Genetic factors contribute to the risk of psychopathology in many psychiatric conditions, but the specific genes are yet to be identified. Neurotransmitter alterations are implicated in the etiology of psychopathology based, in part, on studies of neurotransmitter receptors and their biosynthetic or degradative enzymes in postmortem tissue. Identification of the altered receptors and enzymes serves to identify candidate genes of potential etiological significance. Polymorphisms in these genes can contribute to alterations in protein function in vivo that are part of the neurochemical underpinnings of psychopathologies such as major depressive disorder, psychoses, alcoholism, personality disorders, aggressive-impulsive traits, or suicidal behavior. Altered serotonergic function is implicated in the etiology and pathogenesis of several major psychiatric conditions. In particular, there is much evidence for an association of lower serotonergic function and suicidal behavior. Thus genes related to the serotonergic system are candidate genes worthy of study as part of the genetic diathesis for suicidal behavior. This review examines the following polymorphisms in the serotonin biosynthetic enzyme tryptophan hydroxylase (TPH; A779C substitution), the serotonin transporter (5-HTT, 5-HTTLPR allele), the 5-HT(1B) receptor (G861C, C129T substitution) and the 5-HT(2A) receptor (T102C) for their relationship to suicidal behavior. For the TPH gene, we found the less common U or A allele variant of the A779C polymorphism was associated with suicide attempt. Other studies have found the U allele to be associated with aggression and lower serotonergic function in vivo. A 44 base pair insertion/deletion in the 5' flanking promoter region of the 5-HTT gene may result in less 5-HTT expression and 5-HTT binding. We examined 220 cases postmortem and found no association between the promoter genotype and 5-HTT binding. We also found no association with major depressive disorder (MDD), suicide or pathological aggression, despite finding significantly fewer 5-HTT sites in the prefrontal cortex of depressed and/or suicide cases. In genomic DNA samples from 178 unrelated subjects, we detected two polymorphisms for the 5-HT(1B) receptor at nucleotides 861 and 129. However, no association between either polymorphism and depression, suicide, aggression, or alcoholism was observed. There are two common polymorphisms for the 5-HT(2A) receptor gene in humans. The results of studies of 5-HT(2A) receptor gene polymorphisms do not indicate significant major associations with suicidal behavior. In contrast, the 5-HT(2A) receptor itself is reported to be increased in suicide. Functional polymorphisms involving the promoter region that affect gene expression may explain this finding. Studies of candidate genes related to serotonergic function in brain are increasingly used to establish genetic alterations contributing to psychiatric illness. The most meaningful studies combine the study of candidate genes with direct measures of related proteins as well as psychopathology.