Tryptophan hydroxylase polymorphism and suicidality in unipolar and bipolar affective disorders: a multicenter association study

Association between TPH1 polymorphisms and the risk of suicide behavior: An updated meta-analysis of 18,398 individuals

OBJECTIVES

We aimed to examine the association of TPH1 polymorphisms with the risk of suicide behavior (SB).

DESIGN

Systematic review and meta-analysis.

METHOD

All relevant studies that evaluated the association between the A218C (rs1800532), A779C (rs1799913) and A6526G (rs4537731) polymorphisms and the susceptibility to SB published up to September 2021 were identified through a comprehensive systematic search in PubMed, Scopus, EBSCO and Science Direct electronic databases. The association between TPH1 gene polymorphisms and SB was evaluated using inherence models by odds ratio (OR) and 95% confidence interval (CI). Subgroup analyses, heterogeneity analyses, and publication bias were also tested in this meta-analysis.

RESULTS

The meta-analysis for TPH1 A218C revealed an increased risk of SB in the dominant model (OR = 1.11, 95%CI 1.01-1.22). We also observed a positive association in the allelic (OR = 1.13, 95%CI 1.05-1.21), homozygous (OR = 1.22, 95%CI 1.06-1.40), heterozygous (OR = 1.21, 95%CI 1.08-1.37) and dominant (OR = 1.21, 95%CI 1.09-1.34) inherence models with the suicide attempt. Additionally, in the heterozygous (OR = 0.84, 95%CI 0.73-0.97) and dominant (OR = 0.79, 95%CI 0.68-0.91) inherence models we detected an association with completed suicide. Based on ethnicity, an association of SB in the European population also was observed (OR = 1.29, 95%CI 1.12-1.51). However, for both A779C and A6526G polymorphisms we did not find evidence of an association with SB.

CONCLUSION

This meta-analysis suggests that the A218C polymorphism of TPH1 gene could be a possible risk factor of SB. Future large-scale studies are required to analyze the molecular mechanisms by which affect the susceptibility of developing suicide behavior.

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.

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.

Is there a link between Depressive Disorders and Tryptophan Hydroxylase 1 (TPH1) Gene Polymorphism? - Study from a Distressed Area, Kashmir (India)

Background

The progress that man has made in all domains of life, during all these years of reign over the earth, is utterly remarkable. However, it always came at a price. Each epoch of progress has seen human beings inflicted with trauma and cynical consequences. During the last two decades, Kashmiri (Indian) people have experienced continuous violence, a reign of terror, and political turmoil. Each of these disastrous events has contributed to the increase in psychiatric disorders in this part of the world, especially major depressive disorders. We can observe that besides the environmental influences, gene polymorphism also plays a crucial role in the development of depressive disorders. The role of Tryptophan Hydroxylase 1 (TPH1) gene is implicated in various psychiatric disorders, including depression. However, no study has investigated TPH1 A779C gene polymorphism in depressive disorders in a distressed society like Kashmir (India).

Aims

To study TPH1 A779C single nucleotide polymorphism in depressive disorders in Kashmiri (Indian) population.

Materials and Methods

Two hundred and forty patients diagnosed with depressive disorder, and 160 unrelated healthy volunteers (control), were studied in a case-control study design. Polymorphism was determined using polymerase chain reaction (PCR) and agarose gel electrophoresis, after digestion with HAP II enzyme. Genotypes and allele frequencies were compared using Chi-square tests, Fisher’s exact test, odds ratio, 95% confidence interval (C.I.) and a p-value of <0.05 was considered to be statistically significant.

Results

The mean age ± standard deviation (SD) of depression and control group was 32.02±10.99 and 31.75±9.93, respectively (p= 0.512). It was found that the patients from depression group had AA genotype (51.7%) in comparison to control group (17.5%) and these results were statistically significant (p≤0.0001). Calculation of allelic frequency revealed a stronger association of A allele with depression group (70.83%) than with the control group (41.25%), and it was also found to be statistically significant (p≤0.0001) with C.I. of 3.459 (1.909-6.266).

Conclusion

TPH1 A779C A gene was found to be associated with a major depressive disorder (MDD) in Kashmiri (Indian) population. There were high HAM-A as well as HAM-D scores in depressive patients of Kashmir (India).

A review of genetic alterations in the serotonin pathway and their correlation with psychotic diseases and response to atypical antipsychotics

Serotonin is a neurotransmitter that plays a predominant role in mood regulation. The importance of the serotonin pathway in controlling behavior and mental status is well recognized. All the serotonin elements - serotonin receptors, serotonin transporter, tryptophan hydroxylase and monoamine oxidase proteins - can show alterations in terms of mRNA or protein levels and protein sequence, in schizophrenia and bipolar disorder. Additionally, when examining the genes sequences of all serotonin elements, several single nucleotide polymorphisms (SNPs) have been found to be more prevalent in schizophrenic or bipolar patients than in healthy individuals. Several of these alterations have been associated either with different phenotypes between patients and healthy individuals or with the response of psychiatric patients to the treatment with atypical antipsychotics. The complex pattern of genetic diversity within the serotonin pathway hampers efforts to identify the key variations contributing to an individual's susceptibility to the disease. In this review article, we summarize all genetic alterations found across the serotonin pathway, we provide information on whether and how they affect schizophrenia or bipolar disorder phenotypes, and, on the contribution of familial relationships on their detection frequencies. Furthermore, we provide evidence on whether and how specific gene polymorphisms affect the outcome of schizophrenic or bipolar patients of different ethnic groups, in response to treatment with atypical antipsychotics. All data are discussed thoroughly, providing prospective for future studies.

Epidemiology, neurobiology and pharmacological interventions related to suicide deaths and suicide attempts in bipolar disorder: Part I of a report of the International Society for Bipolar Disorders Task Force on Suicide in Bipolar Disorder

OBJECTIVES

Bipolar disorder is associated with elevated risk of suicide attempts and deaths. Key aims of the International Society for Bipolar Disorders Task Force on Suicide included examining the extant literature on epidemiology, neurobiology and pharmacotherapy related to suicide attempts and deaths in bipolar disorder.

METHODS

Systematic review of studies from 1 January 1980 to 30 May 2014 examining suicide attempts or deaths in bipolar disorder, with a specific focus on the incidence and characterization of suicide attempts and deaths, genetic and non-genetic biological studies and pharmacotherapy studies specific to bipolar disorder. We conducted pooled, weighted analyses of suicide rates.

RESULTS

The pooled suicide rate in bipolar disorder is 164 per 100,000 person-years (95% confidence interval = [5, 324]). Sex-specific data on suicide rates identified a 1.7:1 ratio in men compared to women. People with bipolar disorder account for 3.4-14% of all suicide deaths, with self-poisoning and hanging being the most common methods. Epidemiological studies report that 23-26% of people with bipolar disorder attempt suicide, with higher rates in clinical samples. There are numerous genetic associations with suicide attempts and deaths in bipolar disorder, but few replication studies. Data on treatment with lithium or anticonvulsants are strongly suggestive for prevention of suicide attempts and deaths, but additional data are required before relative anti-suicide effects can be confirmed. There were limited data on potential anti-suicide effects of treatment with antipsychotics or antidepressants.

CONCLUSION

This analysis identified a lower estimated suicide rate in bipolar disorder than what was previously published. Understanding the overall risk of suicide deaths and attempts, and the most common methods, are important building blocks to greater awareness and improved interventions for suicide prevention in bipolar disorder. Replication of genetic findings and stronger prospective data on treatment options are required before more decisive conclusions can be made regarding the neurobiology and specific treatment of suicide risk in bipolar disorder.

Association of TPH-1 and TPH-2 gene polymorphisms with suicidal behavior: a systematic review and meta-analysis

BACKGROUND

It is widely acknowledged that suicidal behavior (SB) has a genetic influence. As a consequence, molecular genetic studies have been mostly conducted on serotonergic genes. One of the most promising candidate genes of this system is tryptophan hydroxylase (TPH). Although there have been several positive studies associating TPH genes and SB, the evidence is not entirely consistent. Therefore, we performed a meta-analysis to gain a better understanding into this issue.

METHODS

The meta-analysis was conducted with 37 articles of genetic association studies of TPH-1 (A218C and A779C) and TPH2 (G-703 T, A-473 T and G19918A) genes. To analyze the association of these variants with SB we used the following models: allelic, additive, dominant and recessive. In addition, we performed a sub-group analysis by Caucasian and Asian populations using the same four models.

RESULTS

TPH-1 gene variants showed a positive significant association with SB, but only in the fixed effects models. With regard to TPH-2 gene variants we could not find an association with SB.

CONCLUSIONS

The study provides evidence that A218C/A779C TPH-1 variants may be a risk factor to manifest SB at the clinical level, which is in agreement with previously reported meta-analyses. With regard to G-703 T/A-473 T/G19918A TPH-2 variants, our up-to-date meta-analysis could not detect any significant association between those genetic variants and SB. However, these results should be interpreted with caution since further studies need to be undertaken using larger sample sizes in different ethnic populations to confirm our findings.

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.

Star-crossed? The association of the 5-HTTLPR s allele with season of birth in a healthy female population, and possible consequences for temperament, depression and suicide

BACKGROUND

Birth season has well-known effects on neuropsychiatric disorders, and may also influence genotype distribution by possibly influencing chance of conception via parental idiosyncratic conception patterns or survival of foetuses or infants. The 5-HTTLPR is associated with phenomena including affective temperaments or suicide which are also associated with birth season. Our aim was to investigate the association of 5-HTTLPR genotype and birth season in a healthy female population.

METHODS

Birth date and 5-HTTLPR genotype was determined for 327 psychiatrically healthy women. The association between presence of s allele and time of birth was analysed using generalized linear models.

RESULTS

A significant association between s allele frequency and time of birth was detected. S allele carrier frequency was marginally significantly higher in July borns and significantly lower in autumn borns.

LIMITATIONS

We investigated an adult sample so genotype frequency data do not reflect birth frequencies. Our sample consisted exclusively of females.

CONCLUSIONS

There is no clear explanation for the observed association, although idiosyncratic parental conception patterns, the association of 5-HTTLPR with sudden infant/intrauterine death, or other s allele-mediated behaviours may play a role. Our results are strikingly parallel with earlier data reporting a higher risk of completed suicide in July borns, and higher scores of July borns and lower scores of autumn borns on certain affective temperament scales, both of which are also associated with the s allele of 5-HTTLPR. Thus our results may add to the growing body of evidence regarding the etiological background of affective disorders.

Interaction between tryptophan hydroxylase I polymorphisms and childhood abuse is associated with increased risk for borderline personality disorder in adulthood

INTRODUCTION

Borderline personality disorder (BPD) is a severe disorder with high morbidity and mortality, but unknown etiology. Childhood abuse has been proposed as an etiological factor, but the mechanism by which an abuse history could influence the risk for BPD has not been determined. The aim of this study was to determine whether the tryptophan hydroxylase 1 (TPH1) gene is related to BPD in a clinical sample, and whether TPH1 genotypes or haplotypes moderate the relationship between abuse history and BPD.

METHODS

Three hundred and ninety-eight patients diagnosed with mood disorders were genotyped for TPH1 G-6526A promoter polymorphism (rs4537731) and the A218C intron 7 polymorphism (rs1800532) and a set of ancestry informative markers, assessed for Diagnostic and Statistical Manual of Mental Disorders, 4th edition diagnoses, and assessed for a history of physical and sexual abuse.

RESULTS

Patients with a diagnosis of BPD were more likely to be risk allele carriers (A alleles at both loci) than the non-BPD group. Logistic regression analysis predicting BPD diagnosis with both single-nucleotide polymorphisms and haplotypes showed significant interaction effects between genotype and abuse history. Poisson regression predicting the number of BPD diagnostic criteria met with the same predictor set also included a significant interaction term. Risk allele carriers with a history of abuse had an increased likelihood of a BPD diagnosis.

CONCLUSION

Variation in TPH1 may increase risk for developing BPD as a result of childhood abuse. Elements of BPD pathology may be due in part to a genetically influenced serotonergic dysfunction, which in turn may lead to a differential response to environmental stressors.

Association between the TPH1 A218C polymorphism and risk of mood disorders and alcohol dependence: evidence from the current studies

BACKGROUND

Several studies have assessed the association between genetic polymorphisms of tryptophan hydroxylase (TPH1) and risk of mood disorders and alcohol dependence, with controversial results. Our aim was to assess the association of TPH1 A218C polymorphism (rs1800532) with mood disorders, including major depressive disorder and bipolar disorder, and alcohol dependence by using meta-analysis.

METHODS

Data were collected from the related literatures published until November 25, 2010 from MEDLINE, EMBASE and ISI Web of Science databases, and meta-analysis stratified by ethnicity was performed in either fixed or random effect model as appropriate by using Stata Statistical Package (version 10.0).

RESULTS

Twenty-seven individual studies were included in the current study, among which, there were 9 studies for bipolar disorder, with 1951 cases and 2161 controls, 14 studies for major depressive disorder, with 2340 cases and 3204 controls, and 4 studies for alcohol dependence, with 601 cases and 711 controls. We found that in Caucasian population, the TPH1 218AA genotype was significantly associated with increased bipolar disorder risk (recessive comparison: OR, 1.42; Bonferroni-adjusted P=0.006; homozygote comparison: OR, 1.63; Bonferroni-adjusted P=0.072), and elevated alcohol dependence risk (recessive comparison: OR, 1.83; Bonferroni-adjusted P=0.012), while the association was not significant in Asian population. Moreover, the A218C polymorphism did not appear to have any effect on major depressive disorder risk either in Caucasians or in Asians.

CONCLUSION

The TPH1 A218C polymorphism is a potential biomarker for bipolar disorder and alcohol dependence risk in Caucasian population.

TPH1 is associated with major depressive disorder but not with SSRI/SNRI response in Taiwanese patients

RATIONALE

Tryptophan hydroxylase 1 (TPH1), which encodes the rate-limiting enzyme tryptophan hydroxylase in the biosynthesis of serotonin, is a candidate gene in the development and treatment response of major depressive disorder (MDD); however, its actual role is uncertain.

OBJECTIVES

We aimed to compare the allele frequencies of TPH1 in MDD patients and healthy controls in Taiwan, and also to investigate the association between TPH1 A218C and treatment response to either fluoxetine or venlafaxine in a Taiwanese population with MDD.

METHODS

One hundred five healthy controls and 115 outpatients diagnosed with MDD were recruited and genotyped for the TPH1 218A/C (rs1800532) polymorphism. Patients were randomized into either the fluoxetine or venlafaxine treatment group. The 21-item Hamilton rating scale for depression (HAM-D) was administered to evaluate depressive symptoms at baseline and bi-weekly over 6 weeks of treatment.

RESULTS

The TPH1 218A/C allele frequencies differed significantly between healthy controls and MDD patients in Taiwan, with a higher prevalence of the A allele in the patient group (p = 0.025). The odds ratio of the A allele to the C allele was 0.507 for the subjects with MDD. There was no significant correlation between the percentage change in HAM-D score and either TPH1 218A/C genotype or TPH1 allele frequencies.

CONCLUSIONS

This study indicated that the TPH1 218A/C genotype and allele frequencies differed between the Taiwanese healthy controls and MDD patients but could not be used to predict treatment outcome in Taiwanese MDD patients. Further research with larger sample sizes is needed to confirm the role of TPH1 218A/C.

Genetic polymorphisms in the SCN8A gene are associated with suicidal behavior in psychiatric disorders in the Chinese population

OBJECTIVES

Suicidal behavior is a serious public health problem which is partly heritable. Identifying the genes and the neurobiologic pathways relevant to suicidal behavior is important for preventative strategies. One family-based study reported an association between sodium channel voltage gated type VIII alpha (SCN8A) and suicidal behavior. In the present study, we aimed to search for SCN8A polymorphisms conferring genetic susceptibility to suicide in the Chinese population.

METHODS

A total of 626 subjects was recruited for the study, including 297 suicide attempters and 329 non-attempters from Shanghai, China. We conducted a case-control association analysis of five SNPs (rs10506302, rs1601012, rs4762004, rs12581041, rs17126078) within the region of SCN8A gene.

RESULTS

we found that two genetic polymorphisms showed statistically significant differences between cases and controls (rs1601012, P=0.004; rs12581041, P=0.01). Moreover, no haplotypes were significantly associated with suicidal behavior in psychiatric disorders after the false discovery rate (FDR) correction. In the analysis of schizophrenia subgroup, three genetic polymorphisms showed statistically significant differences between cases and controls (rs10506302, P=0.024; rs1601012, P=0.004; rs12581041, P=0.004).

CONCLUSIONS

Our findings suggest that the SCN8A gene may be involved in the susceptibility to suicidal behavior among psychiatric disorder patients in the Han Chinese population.

The tryptophan hydroxylase 1 (TPH1) gene, schizophrenia susceptibility, and suicidal behavior: a multi-centre case-control study and meta-analysis

Serotonin (5-hydroxytryptamin; 5-HT) alternations has since long been suspected in the pathophysiology of schizophrenia. Tryptophan hydroxylase (tryptophan 5-monooxygenase; TPH) is the rate-limiting enzyme in the biosynthesis of 5-HT, and sequence variation in intron 6 of the TPH1 gene has been associated with schizophrenia. The minor allele (A) of this polymorphism (A218C) is also more frequent in patients who have attempted suicide and individuals who died by suicide, than in healthy control individuals. In an attempt to replicate previous findings, five single nucleotide polymorphisms (SNPs) were genotyped in 837 Scandinavian schizophrenia patients and 1,473 controls. Three SNPs spanning intron 6 and 7, including the A218C and A779C polymorphisms, were associated with schizophrenia susceptibility (P = 0.019). However there were no differences in allele frequencies of these loci between affected individuals having attempted suicide at least once and patients with no history of suicide attempts (P = 0.84). A systematic literature review and meta-analysis support the A218C polymorphism as a susceptibility locus for schizophrenia (odds ratio 1.17, 95% confidence interval 1.07-1.29). Association studies on suicide attempts are however conflicting (heterogeneity index I(2) = 0.54) and do not support the A218C/A779C polymorphisms being a susceptibility locus for suicidal behavior among individuals diagnosed with a psychiatric disorder (OR = 0.96 [0.80-1.16]). We conclude that the TPH1 A218/A779 locus increases the susceptibility of schizophrenia in Caucasian and Asian populations. In addition, the data at hand suggest that the locus contributes to the liability of psychiatric disorders characterized by elevated suicidal rates, rather than affecting suicidal behavior of individuals suffering from a psychiatric disorder.

TPH2 -703G/T SNP may have important effect on susceptibility to suicidal behavior in major depression

BACKGROUND

Serotonergic system-related genes can be good candidate genes for both major depressive disorder (MDD) and suicidal behavior. In this study, we aimed to investigate the association of serotonin 2A receptor gene -1438A/G SNP (HTR2A -1438A/G), tryptophan hydroxylase 2 gene -703G/T SNP (TPH2 -703G/T) and serotonin 1A receptor C-1019G (HTR1A C-1019G) with suicidal behavior.

METHODS

One hundred and eighty one suicidal depressed patients and 143 non-suicidal depressed patients who met DSM-IV criteria for major depressive disorder were recruited from patients who were admitted to Korea University Ansan Hospital. One hundred seventy six normal controls were healthy volunteers who were recruited by local advertisement. Patients and normal controls were genotyped for HTR2A -1438A/G, TPH2 -703G/T and 5-HT1A C-1019G. The suicidal depressed patients were evaluated by the lethality of individual suicide attempts using Weisman and Worden's risk-rescue rating (RRR) and the Lethality Suicide Attempt Rating Scale-updated (LSARS-II). In order to assess the severity of depressive symptoms of patients, Hamilton's Depression Rating Scale (HDRS) was administered. Genotype and allele frequencies were compared between groups by chi(2) statistics. Association of genotype of the candidate genes with the lethality of suicidal behavior was examined with ANOVA by comparing the mean scores of LSARS and RRR according to the genotype.

RESULTS

There were statistically significant differences in the genotype distributions and allele frequencies of TPH2 -703G/T between the suicidal depressive group and the normal control group. The homozygous allele G (G/G genotype) frequency was significantly higher in suicidal depressed patients than in controls. However, no differences in either genotype distribution or in allele frequencies of HTR2A -1438A/G and HTR1A C-1019G were observed between the suicidal depressed patients, the non-suicidal depressed patients, and the normal controls. There were no differences in the lethality of suicidal behavior in suicidal depressed patients according to the genotypes of three polymorphisms.

CONCLUSION

Our results suggest that TPH2 -703G/T SNP may have an important effect on susceptibility to suicidal behavior. Furthermore, an increased frequency of G allele of TPH2 SNP may be associated with elevated suicidal behavior itself rather than with the diagnosis of major depression and may increase risk of suicidality, independent of diagnosis.

The tryptophan hydroxylase-1 A218C polymorphism is associated with diagnosis, but not suicidal behavior, in borderline personality disorder

While there is some preliminary evidence that the tryptophan hydroxylase I (TPH1) polymorphisms are related to Borderline Personality Disorder (BPD), it is not clear if this association is due to the high rates of suicidal behavior in this patient group. Because of the reported association between TPH1 polymorphisms and suicidal behavior, determining whether TPH1 is related to BPD independent of suicidal behavior is of particular importance. One hundred patients diagnosed with BPD and 101 healthy controls were genotyped for TPH1 intron 7 A218C polymorphism and assessed for impulsiveness and hostility. The BPD patient group had a higher frequency of A allele carriers (AA/AC genotypes) than the control group (chi(2) = 6.12, df = 1, P = 0.01), and differed by genotype frequencies (P = 0.03). Suicide attempter status in the patient group was not related to genotype. Logistic regression analysis controlling for age and gender predicted BPD diagnosis from TPH1 allele group (AA/AC vs. CC, P = 0.03), and TPH1 heterozygotes (AC) appeared to have the highest risk for BPD (P = 0.03). In the full sample, participants with the AC genotype had higher impulsiveness and hostility scores. However, TPH1 did not predict these traits in either of the groups independently, suggesting the association may be an artifact of the association between TPH1 and BPD. Results suggest that the A allele of the tryptophan hydroxylase-1 A218 polymorphism may be associated with BPD, and that it does not appear to be related to suicidal behavior in this population. An aspect of BPD pathology may be due to serotonergic dysfunction.

Serotonin genes and gene-gene interactions in borderline personality disorder in a matched case-control study

Lines of evidence suggest serotonin genes are susceptibility candidates in borderline personality disorder (BPD). However, few molecular genetic studies on BPD have been reported, especially an overall lack of study on epistatic interactions. We genotyped 27 polymorphisms in 7 serotonin genes in 113 Caucasian BPD patients and matched (sex, age and ethnicity) controls. Program UNPHASED was used to perform association analyses for genotypes, alleles and haplotypes with a permutation test of 10,000 simulations. The Multifactor Dimensionality Reduction analysis was used to examine gene-gene interactions in serotonin system, including three other genes (5-HTT, 5-HT2A and MAOA) that we previously reported. Genotype and allele analyses showed that BPD significantly associated with 5-HT2C and TPH2. BPD patients had high frequencies of the 5-HT2C rs6318G allele (p=0.021) and G/G genotype (OR=2.25); and TPH2 rs2171363T allele (p=0.001) and T containing genotypes (OR=3.40). The 5-HT1A, 5-HT1B, 5-HT1D, 5-HT3A and TPH1 showed no significant association with BPD for genotype, allele and haplotype analyses. We also detected significant interactions between 5-HT2C and TPH2 (p=0.001), and among 5-HT2C, 5-HTT, MAOA and TPH2 (p=0.001) in BPD. Patients with 5-HT2C rs6318G/G genotype had a high frequency of TPH2 rs2171363C/T genotype compared with controls. Our study indicates ""that serotonin genes and their interactions may play a role in the susceptibility to borderline personality disorder.

Identification of a CREB-dependent serotonergic pathway and neuronal circuit regulating foraging behavior in Caenorhabditis elegans: a useful model for mental disorders and their treatments?

The cAMP-response element binding protein (CREB)-mediated cell signaling pathway is conserved through evolution and participates in a broad range of complex behaviors of divergent species including man. This study describes the integration of genetic, pharmacologic, and anatomic methods to elucidate a serotonergic signaling pathway by which the CREB homolog CRH-1 controls foraging rate (FR) in the model organism Caenorhabditis elegans, along with the complete neuronal circuit through which this pathway operates. In the anterior afferent arm of the circuit, CRH-1 controls FR by regulating the expression of tph-1, the sole structural gene for tryptophan hydroxylase, in serotonergic sensory (ADF) neurons whose post-synaptic effects are mediated through 5HT(2)-like SER-1 receptors. The posterior afferent limb of the circuit includes an interneuron (RIH) that does not express tph-1 and whose serotonergic phenotype is dependent on the contribution of this neurotransmitter from another source, probably the ADF neurons. The postsynaptic effects of the RIH interneuron are mediated through 5HT(1)-like SER-4 receptors. This model has potential utility for the study of clinical disorders and experimental therapeutics. Furthermore, the discovery of serotonergic neurons that depend on other sources for their neurotransmitter phenotype could provide a mechanism for rapidly altering the number and distribution of serotonergic pathways in developing and adult nervous systems, providing a dimension of functional complexity that has been previously unrecognized.

The tryptophan hydroxylase gene influences risk for bipolar disorder but not major depressive disorder: results of meta-analyses

OBJECTIVE

Tryptophan hydroxylase is the rate-limiting enzyme in the synthesis of serotonin, and thus its gene, TPH, has been extensively studied as a risk factor for both bipolar disorder and major depressive disorder. The purpose of the present report is to synthesize the available data on these putative associations and derive best estimates of the nature and magnitude of the influence of TPH on risk for mood disorders.

METHODS

We identified studies that examined the TPH A218C polymorphism in relation to major depressive disorder or bipolar disorder using the PubMed online search engine, ultimately including 10 case-control studies in two meta-analyses.

RESULTS

The AA genotype had a significant effect on risk for bipolar disorder in comparison to either the CC or AC genotypes, suggesting that the A allele may increase risk for bipolar disorder in a recessive manner. None of the three genotypes significantly increased risk for major depressive disorder relative to any of the other genotypes.

CONCLUSION

The homozygous recessive genotype of the TPH A218C polymorphism has a significant effect on risk for bipolar disorder but not major depressive disorder. A possible explanation for these results is that the A allele influences mood by permitting or facilitating mania while having no effect on depression. Further replication of these findings in additional large case-control and family-based association is needed before TPH can be designated a risk gene for bipolar disorder.

The genetics of bipolar disorder: genome 'hot regions,' genes, new potential candidates and future directions

Bipolar disorder (BP) is a complex disorder caused by a number of liability genes interacting with the environment. In recent years, a large number of linkage and association studies have been conducted producing an extremely large number of findings often not replicated or partially replicated. Further, results from linkage and association studies are not always easily comparable. Unfortunately, at present a comprehensive coverage of available evidence is still lacking. In the present paper, we summarized results obtained from both linkage and association studies in BP. Further, we indicated new potential interesting genes, located in genome 'hot regions' for BP and being expressed in the brain. We reviewed published studies on the subject till December 2007. We precisely localized regions where positive linkage has been found, by the NCBI Map viewer (http://www.ncbi.nlm.nih.gov/mapview/); further, we identified genes located in interesting areas and expressed in the brain, by the Entrez gene, Unigene databases (http://www.ncbi.nlm.nih.gov/entrez/) and Human Protein Reference Database (http://www.hprd.org); these genes could be of interest in future investigations. The review of association studies gave interesting results, as a number of genes seem to be definitively involved in BP, such as SLC6A4, TPH2, DRD4, SLC6A3, DAOA, DTNBP1, NRG1, DISC1 and BDNF. A number of promising genes, which received independent confirmations, and genes that have to be further investigated in BP, have been also systematically listed. In conclusion, the combination of linkage and association approaches provided a number of liability genes. Nevertheless, other approaches are required to disentangle conflicting findings, such as gene interaction analyses, interaction with psychosocial and environmental factors and, finally, endophenotype investigations.

Meta-analyses of genetic studies on major depressive disorder

The genetic basis of major depressive disorder (MDD) has been investigated extensively, but the identification of MDD genes has been hampered by conflicting results from underpowered studies. We review all MDD case-control genetic association studies published before June 2007 and perform meta-analyses for polymorphisms that had been investigated in at least three studies. The study selection and data extraction were performed in duplicate by two independent investigators. The 183 papers that met our criteria studied 393 polymorphisms in 102 genes. Twenty-two polymorphisms (6%) were investigated in at least three studies. Seven polymorphisms had been evaluated in previous meta-analyses, 5 of these had new data available. Hence, we performed meta-analyses for 20 polymorphisms in 18 genes. Pooled odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Statistically significant associations were found for the APOE varepsilon2 (OR, 0.51), GNB3 825T (OR, 1.38), MTHFR 677T (OR, 1.20), SLC6A4 44 bp Ins/Del S (OR, 1.11) alleles and the SLC6A3 40 bpVNTR 9/10 genotype (OR, 2.06). To date, there is statistically significant evidence for six MDD susceptibility genes (APOE, DRD4, GNB3, MTHFR, SLC6A3 and SLC6A4).

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 unipolar depression with gene polymorphisms in the serotonergic pathways in Han Chinese

OBJECTIVE

The present study aims to investigate the association of unipolar depression (UPD) with six serotonergic gene polymorphisms in Han Chinese.

METHODS

One hundred and thirty-two UPD patients and 180 healthy controls were genotyped for polymorphisms of six serotonergic genes, including tryptophan hydroxylase (TPH1 A218C), serotonin transporter promoter region (5-HTTLPR), serotonin receptor 2A (5-HT2AR -1438G/A), serotonin receptor 2C (5-HT2CR Cys23Ser), serotonin receptor 6 (5-HT6R C267T) and serotonin receptor 1Dβ (5-HT1DβR T371G). Symptomatic clusters were evaluated by the 24-item Hamilton Rating Scale for Depression (HAMD).

RESULTS

The frequencies of S/S genotype and S allele in 5-HTTLPR polymorphism were significantly higher in UPD patients than in healthy controls. There was a significant difference in distributions of genotypes in 5-HT2CR Cys23Ser polymorphism between UPD patients and control subjects, but the difference became no significant when the data were further stratified by gender. The patients with genotypes G/G and T/G of 5-HT1DβR T371G polymorphism had significantly lower scores of diurnal variation evaluated by HAMD than those with genotype T/T, while the patients with genotype T/G had significantly higher scores of hopelessness than those with genotypes G/G and T/T. There were no significant differences in genotypic and allelic distributions of TPH1 A218C, 5-HT2AR -1438G/A or 5-HT6R C267T polymorphisms between the case and control groups.

CONCLUSION

The study demonstrates that 5-HTTLPR and 5-HT2CR Cys23Ser polymorphisms might contribute to susceptibility of UPD, and the genotype T/T in 5-HT1DβR T371G polymorphism might be a risk factor for diurnal variation, while T/G might be a protective factor against hopelessness in Han Chinese populations.

Diminished 5-HT functioning in CBCL pediatric bipolar disorder-profiled ADHD patients versus normal ADHD: susceptibility to rapid tryptophan depletion influences reaction time performance

OBJECTIVE

There is a current debate on characterizing children with pediatric bipolar disorder (PBD) through a profile within the child behaviour checklist (CBCL), and on the involvement of the 5-HT system in the underlying neurobiological processes of PBD. The aim of the present paper was to investigate reaction time performance in patients with CBCL-PBD and to discriminate ADHD from ADHD with CBCL-PBD with respect to diminished 5-HT functioning and reaction time.

METHODS

Twenty-two patients with ADHD received the rapid tryptophan depletion test (RTD) thus lowering the central-nervous 5-HT synthesis rate within a placebo-controlled double-blind within-subject crossover design. Reaction time was assessed using a competitive reaction time game with low and high provocation after both depletion and placebo intake. The study sample was divided into high and low scorers according to their CBCL-PBD scores.

RESULTS

Comparing those six patients with the highest and clinically significant CBCL-PBD scores versus those six patients with the lowest, patients with a high CBCL-PBD score showed a slower reaction time under RTD compared to patients with low CBCL-PBD scores after high provocation. CBCL-'aggression' discriminated between the two groups.

CONCLUSIONS

The results suggest alterations in 5-HT functioning in CBCL-PBD-spectrum patients, and 'aggression' as a potential moderator variable to ADHD.

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.

Molecular genetics of bipolar disorder

Bipolar disorder (BPD) is an often devastating illness characterized by extreme mood dysregulation. Although family, twin and adoption studies consistently indicate a strong genetic component, specific genes that contribute to the illness remain unclear. This study gives an overview of linkage studies of BPD, concluding that the regions with the best evidence for linkage include areas on chromosomes 2p, 4p, 4q, 6q, 8q, 11p, 12q, 13q, 16p, 16q, 18p, 18q, 21q, 22q and Xq. Association studies are summarized, which support a possible role for numerous candidate genes in BPD including COMT, DAT, HTR4, DRD4, DRD2, HTR2A, 5-HTT, the G72/G30 complex, DISC1, P2RX7, MAOA and BDNF. Animal models related to bipolar illness are also reviewed, with special attention paid to those with clear genetic implications. We conclude with suggestions for strategies that may help clarify the genetic bases of this complex illness.

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.

Further clarification of the contribution of the tryptophan hydroxylase (TPH) gene to suicidal behavior using systematic allelic and genotypic meta-analyses

Suicide is a major public health issue, especially in western countries, accounting for approximately 1 million deaths every year throughout the world. The tryptophan hydroxylase (TPH) gene has been extensively studied as a candidate for suicidal behavior due to its role in serotonergic neurotransmission. Since the first study associating the gene with schizophrenia, there have been many attempts to replicate it. However, a number of these studies have produced contrary results, possibly reflecting inadequate statistical power and the use of different populations. Association data relating European and, more particularly, Asian populations has become increasingly available in recent years. To examine whether the aggregate data provide evidence of statistical significance, the current meta-analysis has combined all the published studies up to July 2005, and examined the polymorphisms (A779C, A218C, A-6526G) in the context of varied suicidal behaviors by analyzing the studies in total and in subsets. Compared with the inconsistent results of previous studies, the current results (22 references) confirm a strong overall association between suicidal behavior and the A779C/A218C polymorphisms, supporting the involvement of TPH in the pathogenesis of suicidal behavior.

Identification of first candidate genes for creativity: a pilot study

Studies from behavioral genetics have demonstrated the high heritability of intelligence. However, the endeavor to detect the genes forming the molecular basis of intelligence has been rather unsuccessful until now. Pharmacological studies have demonstrated the influence of the dopaminergic (DA) and the serotonergic (5-HT) system on subcomponents of cognitive functioning, and first studies from molecular genetics have demonstrated that genes related to the DA metabolism are associated with mental abilities. However, candidate genes for creativity have not been identified so far. Therefore, the influence of the catechol-O-methyltransferase (locus: COMT VAL158MET) gene and the dopamine D2 receptor gene (locus: DRD2 TAQ IA) on creativity was tested in addition to a serotonergic gene, TPH1 (locus: TPH-A779C), in a sample of N = 92 healthy Caucasian subjects while controlling for intelligence. Results showed that the DRD2 gene and the TPH gene were both associated with total creativity, explaining 9% of the variance, while COMT was not related to creativity at all. With respect to the subcomponents, the A1+ allele of DRD2 was related to higher verbal creativity as compared to the A1- allele, and carriers of the A allele of TPH1 showed significantly higher scores in figural and in numeric creativity, indicating that the two gene loci discriminate between higher cortical functions according to the organization of cognitive functions in the respective hemispheres.

Interaction between the tryptophan hydroxylase gene and the serotonin transporter gene in schizophrenia but not in bipolar or unipolar affective disorders

Increasing focus is being given to identify possible combinations of genes related to specific clinical phenotypes. In our sample of 814 patients comprising 114 with schizophrenia, 416 with bipolar affective disorder and 284 with unipolar affective disorder, we studied interactions between the tryptophan hydroxylase (TPH), the serotonin transporter (5-HTTLPR), and the dopamine receptor (DRD4) genes in relation to five major psychiatric symptomatology scores. There was significant interaction between the TPH and the 5-HTTLPR genes. With an increasing number of short (s) alleles of 5-HTTLPR, the scores for delusions, disorganization and negative symptoms were significantly decreasing among subjects having the TPH genotype AA but increasing among subjects having the TPH genotype AC, yielding the highest scores for the combinations AA x ll and AC x ss. Since high scores on just delusions, disorganization and negative symptoms but low scores on excitement and depression were found among subjects with schizophrenia, we conducted comparisons among the three diagnostic categories and controls as regards the combined TPH x 5-HTTLPR genotype distribution. Schizophrenia subjects had a significantly different distribution of the genotype combination for TPH x 5-HTTLPR as compared to 241 controls or to unipolar or bipolar subjects, and had significantly higher frequencies of AA x ll and of AC x ss. Thus, an interaction between TPH and 5-HTTLPR genes constitutes susceptibility to schizophrenia, thereby yielding apparent relationships between the major psychiatric symptomatology scores and genotype combinations in samples that are obtained by pooling schizophrenia with other diagnostic categories.

Two types of aggression are differentially related to serotonergic activity and the A779C TPH polymorphism

The authors investigated whether different types of aggression relate to the A779C tryptophan hydroxylase (TPH) polymorphism and to serotonergic activity in volunteers. A factor analysis of the Buss-Durkee Hostility Inventory yielded 2 factors representing Neurotic Hostility (NH) and Aggressive Hostility (AH). The authors used a neuroendocrine challenge with Citalopram in 48 volunteers and increased cortisol concentrations only in those with high levels of AH. Finally, an association study with 58 volunteers revealed that the A779C TPH polymorphism significantly relates to AH, with the highest aggression levels for the genotype AA and the lowest aggression levels for the genotype CC, but not to NH. Results are discussed with respect to inconsistent findings in the literature, which may be explained by this distinction of types of aggression.

Pleiotropic effect of the TPH A779C polymorphism on nicotine dependence and personality

Recent studies from molecular genetics have suggested an association between the tryptophan hydroxylase 1 (TPH1) gene and nicotine addiction indicating a dysfunction of the serotonergic (5-HT) system in smoking behavior. In a sample of 252 healthy subjects, a significant association between variations observed in nicotine dependence and the heterozygous AC-genotype of the TPH A779C polymorphism could be demonstrated. Moreover, the heterozygous genotype was significantly associated with a personality trait of neurotic aggression (indirect hostility, negativism), as measured by the Buss-Durkee-Hostility-Inventory (BDHI). The positive heterosis effects with respect to nicotine addiction and personality support the idea that the TPH1 gene exerts pleiotropic effects.

Genetic association between the phospholipase A2 gene and unipolar affective disorder: a multicentre case-control study

The co-segregation in one pedigree of bipolar affective disorder with Darier's disease whose gene is on chromosome 12q23-q24.1, and findings from linkage and association studies with the neighbouring gene of phospholipase A2 (PLA2) indicate that PLA2 may be considered as a candidate gene for affective disorders. All relevant genetic association studies, however, were conducted on bipolar patients. In the present study, the possible association between the PLA2 gene and unipolar affective disorder was examined on 321 unipolar patients and 604 controls (all personally interviewed), recruited from six countries (Belgium, Bulgaria, Croatia, Germany, Greece, and Italy) participating in the European Collaborative Project on Affective Disorders. After controlling for population group and gender, one of the eight alleles of the investigated marker (allele 7) was found to be more frequent among unipolar patients with more than three major depressive episodes than among controls (P<0.01); genotypic association was also observed, under the dominant model of genetic transmission (P<0.02). In addition, presence of allele 7 was correlated with a higher frequency of depressive episodes (P<0.02). These findings suggest that structural variations at the PLA2 gene or the chromosomal region around it may confer susceptibility for unipolar affective disorder.

Monoamine Oxidase A and Tryptophan Hydroxylase Gene Polymorphisms

Most of the candidate gene studies in bipolar disorder have focused on the major neurotransmitter systems that are influenced by drugs used in the treatment of this disorder. The monoamine oxidase A (MAOA) and the tryptophan hydroxylase (TPH1, TPH2) genes are two of the candidates that have been tested in a series of association studies using unrelated or family-based controls. This review summarizes the existing association studies regarding these genes. Most of these studies were based on the unrelated case-control design with samples of 50 to 600 subjects. Regarding MAOA, three meta-analyses with partially overlapping samples supported a modest effect of this gene in bipolar disorder in female Caucasians. However, as several studies could not replicate these findings, more work is necessary to demonstrate unequivocally the involvement of MAOA in bipolar disorder and establish the biological mechanism underlying the genetic association. With respect to TPH1 and TPH2, the majority of studies did not provide evidence for an association between these genes and bipolar disorder. The genes are more likely to be related to suicidal behavior than to bipolar disorder.

Molecular genetics of affective disorders

Evidence for familial aggregation in Affective Disorders (AD) has been provided in classical studies. Linkage and association genetic studies have been proposed to detect genetic factors implicated in AD. However, findings from molecular genetic studies remain inconclusive. Nevertheless, current research is focusing on the phenotypes, both sub- and endophenotypes. In addition, recent advances in technology, such as microarrays, provide new tools in psychiatric genetics. These different approaches offer a new optimism era in the search of genetic factors in AD.

Association between the TPH gene A218C polymorphism and suicidal behavior: a meta-analysis

Genes encoding proteins involved in serotonergic metabolism are major candidates in association studies of suicidal behavior. The tryptophan hydroxylase (TPH) gene, which codes for the rate-limiting enzyme of serotonin biosynthesis, is a major candidate gene and has been extensively studied in association studies of suicidal behavior, providing conflicting results. It is difficult to interpret these conflicting results due to lack of power, ethnic heterogeneity, and variations in the sampling strategies (in particular for controls) and in the polymorphism of the TPH gene studied. Meta-analyses can improve the statistical power for the analysis of the effects of candidate vulnerability factors. The analysis of the sources of heterogeneity that contribute to these conflicting results is an important step in the interpretation of these conflicting association results and in the interpretation of the results of a meta-analysis. We selected all of the published association studies between the TPH gene polymorphism and suicidal behavior. Nine association studies between the A218C TPH polymorphism and suicidal behavior fulfilled the inclusion criteria. A significant association was observed between the A218C polymorphism and suicidal behavior using the fixed effect method (odds ratio (OR) = 1.62; 95% confidence interval (CI) = [1.26; 2.07]) and the random effect method (OR = 1.61; 95% CI = [1.11; 2.35]). The analysis of the sources of heterogeneity showed that two studies (one positive and one negative) significantly deviated from the calculated global effect. The meta-analysis performed after removing those two studies also revealed a significant association between the TPH A218C polymorphism and suicidal behavior. Both analyses suggested that the A allele has a dose-dependent effect on the risk of suicidal behavior.

A unique central tryptophan hydroxylase isoform

Serotonin (5-hydroxytryptophan, 5-HT) is a neurotransmitter synthesized in the raphe nuclei of the brain stem and involved in the central control of food intake, sleep, and mood. Accordingly, dysfunction of the serotonin system has been implicated in the pathogenesis of psychiatric diseases. At the same time, serotonin is a peripheral hormone produced mainly by enterochromaffin cells in the intestine and stored in platelets, where it is involved in vasoconstriction, haemostasis, and the control of immune responses. Moreover, serotonin is a precursor for melatonin and is therefore synthesized in high amounts in the pineal gland. Tryptophan hydroxylase (TPH) catalyzes the rate limiting step in 5-HT synthesis. Until recently, only one gene encoding TPH was described for vertebrates. By gene targeting, we functionally ablated this gene in mice. To our surprise, the resulting animals, although being deficient for serotonin in the periphery and in the pineal gland, exhibited close to normal levels of 5-HT in the brain stem. This led us to the detection of a second TPH gene in the genome of humans, mice, and rats, called TPH2. This gene is predominantly expressed in the brain stem, while the classical TPH gene, now called TPH1, is expressed in the gut, pineal gland, spleen, and thymus. These findings clarify puzzling data, which have been collected over the last decades about partially purified TPH proteins with different characteristics and justify a new concept of the serotonin system. In fact, there are two serotonin systems in vertebrates, independently regulated and with distinct functions.

Case-control and linkage disequilibrium studies of the tryptophan hydroxylase gene polymorphisms and major depressive disorder

OBJECTIVES

Alterations in the level of the serotonin, serotonin uptake and the number of binding sites have been linked to affective illness. We investigated the association of tryptophan hydroxylase gene polymorphisms and unipolar depression in a case-control study design.

METHODS

Patients and ethnically matched controls were genotyped for three polymorphisms of the tryptophan hydroxylase gene. RESULTS Significant difference in genotype frequency between patient and control groups was observed for the IVS7+218A >C polymorphism but not for the two promoter polymorphisms -1067G >A and -347T >G. Strong linkage disequilibrium among the three polymorphisms was also observed.

CONCLUSIONS

As the sample size was small, the positive association would need to be replicated by family-based association studies or in a larger set of samples. As our results did not indicate association with either of the two promoter polymorphisms, there is a need to continue the search for the causative variant directly involved in the susceptibility to unipolar depression in Chinese as this polymorphism within the intron might not be the true susceptibility variant.

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.

Genetic variations in tryptophan hydroxylase in suicidal behavior: analysis and meta-analysis

BACKGROUND

Neurobiological studies implicate serotonergic dysfunction in suicidal behavior. Tryptophan hydroxylase (TPH), the rate-limiting enzyme in the biosynthesis of serotonin, plays a vital role in serotonin metabolism. Thus, variations in the TPH gene have been regarded as prime candidates in the susceptibility to suicidal behavior. The most widely studied genetic variations in the TPH gene, which are located in intron 7, yielded conflicting results in individual studies on suicide-related behavior.

METHODS

We performed a meta-analysis on a total of 898 patients and 1179 control subjects, in addition to our local association study in consecutively recruited suicide attempters (n=147) and healthy control subjects of German descent (n=326).

RESULTS

We observed a nonsignificant higher frequency of the TPH intron 7 A218 allele in our local group. The meta-analysis showed a weak yet highly significant increase in the frequency of the A218 allele (odds ratio [OR]: 1.33; 95% confidence interval [CI]: 1.17-1.50; p=.00002) and an over-representation of A-carriers (OR: 1.48; 95% CI: 1.22-1.79; p=.00005) in Caucasian suicide attempters/victims.

CONCLUSIONS

Our meta-analysis provides strong evidence for an association of suicide-related behavior with an A218 single-nucleotide polymorphism in the TPH gene in Caucasians. Because this variation do not seem to alter functional properties of the TPH gene or protein, functional variations remain to be identified and subsequently tested for association with suicide-related behavior.

Gene-environment interaction in psychiatric disorders as indicated by season of birth variations in tryptophan hydroxylase (TPH), serotonin transporter (5-HTTLPR) and dopamine receptor (DRD4) gene polymorphisms

Genetic and environmental factors, as well as their interactions, are likely to be involved in psychiatric disorders. Considerable progress has been made in association and linkage studies with various candidate genes, at times with conflicting or ambiguous results. An environmental factor that has persistently shown associations with several psychiatric and neurological disorders is the season of birth. If it is the interaction of a specific gene allele with a specific season of birth that constitutes an increased (or decreased) risk for a disorder, then the individuals with this disorder are likely to have a season of birth variation in this gene allele. We investigated the variations in TPH, 5-HTTLPR and DRD4 gene polymorphisms according to seasonality of birth in 954 patients with unipolar affective disorder, bipolar affective disorder, and schizophrenia, respectively, and in 395 controls. We first analyzed season of birth variations in the gene alleles with one cycle or two cycles per year, and then compared specified birth seasons with each other. We found season of birth variations in these gene alleles that were different for different psychiatric disorders. Significant differences between cases and controls could be obtained when restricting the analysis within certain birth seasons but not within others. Our results thus suggest an interaction between the seasons of birth and the expression of the candidate genes, and that season of birth is a confounding variable when investigating the role of the candidate genes in susceptibility to psychiatric disorders.

Association of anger-related traits with SNPs in the TPH gene

Since both aggression-related traits and serotonergic activity are partially heritable and correlate inversely, variations in genes of the serotonergic system might then, to some extent, account for variations in aggression-related behavior. Tryptophan hydroxylase (TPH) is the rate limiting biosynthetic enzyme in the serotonin pathway and regulates levels of serotonin. Recently, a genetic variation in TPH has been associated with aggression and anger-related traits in volunteers. We investigated a sample of community-based healthy volunteers (n = 154) and suicide attempters (n = 86), a clinical population with a high risk for elevated impulsive aggression and related traits. The subjects were genotyped for a A218C and a A779C single nucleotide polymorphism (SNP) located in the TPH gene. All subjects were administered standard psychiatric interviews as well as self-report questionnaires for aggression, irritability and anger-related traits. For anger-related traits, a multivariate effect of the tryptophan hydroxylase genotype and an interaction effect for genotype and diagnosis was observed in healthy volunteers and suicide attempters after controlling for age and educational level. U-carriers in both groups showed higher scores for State Anger, Trait Anger and Angry Temperament. These findings support the hypothesis that the A218C and the A779C SNP in the TPH gene may be associated with anger-related traits in German samples.

Primer on medical genomics. Part VI: Genomics and molecular genetics in clinical practice

An important milestone in medical science is the recent completion of a "working draft" of the human genome sequence. The identification of all human genes and their regulatory regions provides the framework to expedite our understanding of the molecular basis of disease. This advance has also formed the foundation for a broad range of genomic tools that can be applied to medical science. These developments in global gene and gene product analysis as well as targeted molecular genetic testing are destined to change the practice of modern medicine. Despite these exciting advances, many practicing clinicians perceive that the role of molecular genetics, especially that of genomics, is confined primarily to the research arena with little current clinical applicability. The aim of this article is to highlight advances in DNA/RNA-based methods of susceptibility screening, disease diagnosis and prognostication, and prediction of treatment outcome in regard to both drug toxicity and response as they apply to various areas of clinical medicine.

Molecular genetics in the analysis of suicide

Each year, one million people die of suicide. Among the different identified risk factors, genetic factors seem to be part of a multidimensional behavior, including psychiatric, psychosocial, biological factors and physical illness. Family studies have provided evidence for familial transmission in suicide, confirmed in twin and adoption studies. At a molecular level, serotonin seems to be one of the key neurotransmitters implicated in suicidal behavior. Therefore, genes coding for proteins involved in serotonergic neurotransmission have been extensively studied in case-control association studies on suicide. Major findings concern Tryptophan hydroxylase (TPH) gene, particularly in violent suicidal behavior. Though they may seem contradictory, studies on Serotonin transporter (5-HTT), Monaomine oxidase (MAOA), Serotonin 2A and 2C receptors (5-HT2A and 5-HT2C) and Tyrosine hydroxylase (TH) genes are promising. In spite of those observations having some limitations, it appears that genetic factors are a serious risk factor, besides environmental aspects of suicidal behavior.

Manic-depression genes and the new millennium: poised for discovery

Manic-depressive illness is a common psychiatric disorder with complex etiology that likely involves multiple genes and non-genetic influences. The uncertain path to gene discovery has spurred considerable debate over genetic findings and gene-finding strategies. In this article, I review the main findings, with a focus on: (1) putative linked loci on chromosomes 1q31-32, 4p16, 6pter-p24, 10p14, 10q21-26, 12q23-24, 13q31-32, 18p11, 18q21-23, 21q22, 22q11-13, and Xq24-28; and (2) association studies with candidate genes, dynamic mutations, mitochondrial mutations, and chromosomal aberrations. Although no gene has been identified, promising findings are emerging. I then discuss the challenges and opportunities ahead, with special emphasis on gene-finding methods-in particular, questions pertaining to phenotype definition, linkage and association mapping, gene markers, sampling, study population, multigene systems, lessons from other disorders, animal models, and bioinformatics. The progress to date, together with rapid advances in genomics, analytical and computational methods, and bioinformatics, holds promise for new insights into the genetics of manic-depression, in the new millennium.

Meta-analysis of the association between tryptophan hydroxylase and suicidal behavior

Tryptophan hydroxylase (TPH) has been the candidate gene of focus in many of the association studies of suicidal behavior in recent years. Initial positive findings with respect to an association between the TPH gene and suicidal behavior have been replicated, but not consistently. Typically, individual studies have investigated small samples, and thus they repeatedly had insufficient statistical power to detect a positive association. Meta-analysis is one approach that can be used to achieve greater statistical power and may be helpful in providing a more conclusive understanding. We used meta-analytic techniques to investigate the association between an intron 7 polymorphism in the TPH gene and suicidal behavior. A total of 39 publications were identified and reviewed, 17 of which were selected for inclusion in this study. We performed two meta-analyses. One compared suicide attempters or completers (N = 1,290) with healthy controls (N = 2,295); the other compared suicide attempters (N = 625) with nonattempters (N = 1,475). None of these studies provided evidence for association (odds ratio (OR) = 1.14, 95% confidence interval (CI) = 0.97-1.34 for the former and OR = 0.96, 95% CI = 0.77-1.20 for the latter). The combined results from comparisons within both groups showed no overall association between suicidal behavior and an intron 7 polymorphism of the TPH gene.