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

Genetics of suicide ideation. A role for inflammation and neuroplasticity?

Suicide is a leading cause of death worldwide. Suicide ideation (SI) is a known risk factor for suicide behaviour (SB). The current psychobiology and genetic predisposition to SI and SB are poorly defined. Despite convincing relevance of a genetic background for SI, there is no current implementable knowledge about the genetic makeup that identifies subjects at risk for it. One of the possible reasons for the absence of a clear-cut evidence is the polygenetic nature of SI along with the very large sample sizes that are needed to observe significant genetic association result. The CATIE sample was instrumental to the analysis. SI was retrieved as measured by the Calgary test. Clinical possible covariates were identified by a nested regression model. A principal component analysis helped in defining the possible genetic stratification factors. A GWAS analysis, polygenic risk score associated with a random forest analysis and a molecular pathway analysis were undertaken to identify the genetic contribution to SI. As a result, 741 Schizophrenic individuals from the CATIE were available for the genetic analysis, including 166,325 SNPs after quality control and pruning. No GWAS significant result was found. The random forest analysis conducted by combining the polygenic risk score and several clinical variables resulted in a possibly overfitting model (OOB error rate < 1%). The molecular pathway analysis revealed several molecular pathways possibly involved in SI, of which those involved in microglia functioning were of particular interest. A medium-small sample of SKZ individuals was analyzed to shed a light on the genetic of SI. As an expected result from the underpowered sample, no GWAS positive result was retrieved, but the molecular pathway analysis indicated a possible role of microglia and neurodevelopment in SI.

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.

The neurobiology of human aggressive behavior: Neuroimaging, genetic, and neurochemical aspects

In modern societies, there is a strive to improve the quality of life related to risk of crimes which inevitably requires a better understanding of brain determinants and mediators of aggression. Neurobiology provides powerful tools to achieve this end. Pre-clinical and clinical studies show that changes in regional volumes, metabolism-function and connectivity within specific neural networks are related to aggression. Subregions of prefrontal cortex, insula, amygdala, basal ganglia and hippocampus play a major role within these circuits and have been consistently implicated in biology of aggression. Genetic variations in proteins regulating the synthesis, degradation, and transport of serotonin and dopamine as well as their signal transduction have been found to mediate behavioral variability observed in aggression. Gene-gene and gene-environment interactions represent additional important risk factors for aggressiveness. Considering the social burden of pathological forms of aggression, more basic and translational studies should be conducted to accelerate applications to clinical practice, justice courts, and policy making.

Association of TPH1 and serotonin transporter genotypes with treatment response for suicidal ideation: a preliminary study

Variants in three genes coding for components of the serotonergic system, the tryptophan hydroxylase 1 (TPH1) rs1799913, serotonin transporter (SLC6A4) 5-HTTLPR, and serotonin receptor 2A (HTR2A) rs6311, were evaluated for association with suicidal ideation (SI) and with recovery from SI in a psychiatric inpatient population. Five hundred and eighty-two adult inpatients, including 390 patients who had SI, collected from December 2012 to April 2016 were assessed. SI recovery, calculated as change in SI between the first two-week period after admission and weeks 5 and 6, was appraised for association with the three variants. In this preliminary study, both TPH1 and 5-HTTLPR genotypes were associated with recovery (TPH1: recessive model, increased recovery with AC genotype, P = 0.026; additive model, increased recovery with AC genotype, P = 0.037; 5-HTTLPR: recessive model, increased recovery with AC, P = 0.043). When patients with comorbid alcohol use disorder (AUD) were removed, given that TPH1 has been associated with alcoholism, the associations of those recovered from SI with TPH1 rs1799913 remained significant for the additive (increased recovery with AC, P = 0.045) and recessive (increased recovery with C-carriers, P = 0.008) models, and with 5-HTTLPR using the dominant model (increased recovery with S'S', P = 0.016). In females, an association of SI recovery with TPH1 rs1799913 was found using a recessive model (increased recovery with C-carriers, P = 0.031), with 5-HTTLPR using additive (increased recovery with L'S', P = 0.048) and recessive (increased recovery with S'S', P = 0.042) models. Additionally, an association of SI with TPH1 rs1799913 was found in females using both additive (increased risk in AC, P = 0.033) and recessive (increased risk in C-carriers, P = 0.043) models, and with 5-HTTLPR using a recessive model (increased risk in S'S', P = 0.030). This study provides evidence that variation in the TPH1 and serotonin transporter genes play key roles in moderating recovery from SI during treatment in an inpatient psychiatric clinic.

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.

A biopsychosocial evaluation of the risk for suicide in schizophrenia

The risk of suicide is greatly increased in individuals with schizophrenia. Previous research has identified several potential risk factors for suicidal behavior in schizophrenia, although their ability to independently predict suicide is limited. The objective of this review was to systematically analyze and identify the interaction between the proposed risk factors in the literature that may predict suicidal behavior in schizophrenia. Articles that explored suicidal behavior and suicide risk in schizophrenia that were published between 1980 and August of 2015, indexed in PubMed, MEDLINE, and Scopus were systematically reviewed. Many studies proposed a range of biopsychosocial risk factors that may independently lead to suicide in schizophrenia. These risk factors appear to be mainly related to stress, a history of suicidal behavior, and psychotic symptoms. It is clear, however, that many of these factors do not act independently and in fact require the reciprocal interaction of several of them to pose a risk for suicide in schizophrenia. Independently, the power of many risk factors to predict suicide is limited. Future studies should continue to adopt a multidimensional approach by considering the interaction of several factors in assessing the risk for suicide in schizophrenia.

Functions and Signaling Pathways of Amino Acids in Intestinal Inflammation

Intestine is always exposed to external environment and intestinal microorganism; thus it is more sensitive to dysfunction and dysbiosis, leading to intestinal inflammation, such as inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), and diarrhea. An increasing number of studies indicate that dietary amino acids play significant roles in preventing and treating intestinal inflammation. The review aims to summarize the functions and signaling mechanisms of amino acids in intestinal inflammation. Amino acids, including essential amino acids (EAAs), conditionally essential amino acids (CEAAs), and nonessential amino acids (NEAAs), improve the functions of intestinal barrier and expressions of anti-inflammatory cytokines and tight junction proteins but decrease oxidative stress and the apoptosis of enterocytes as well as the expressions of proinflammatory cytokines in the intestinal inflammation. The functions of amino acids are associated with various signaling pathways, including mechanistic target of rapamycin (mTOR), inducible nitric oxide synthase (iNOS), calcium-sensing receptor (CaSR), nuclear factor-kappa-B (NF-κB), mitogen-activated protein kinase (MAPK), nuclear erythroid-related factor 2 (Nrf2), general controlled nonrepressed kinase 2 (GCN2), and angiotensin-converting enzyme 2 (ACE2).

Suicide behavior as a quantitative trait and its genetic background

INTRODUCTION

Studies have not given yet a clear answer what is the genetic background of suicidal predisposition. The associations between polymorphisms of the TPH1 and 5-HTTLPR genes and violent suicidal behavior was revealed with the least inconsistencies.

METHOD

We selected 10 "strong candidate genes" and 35 SNPs, SLC6A4 and ACP1 for replication study. We searched associations between precisely described suicidal phenotype in 825 affective patients and polymorphisms of selected neurobiological pathways genes as well as their interactions that constitute suicidal risk.

RESULTS

The results confirm the role of TPH1, TPH2, 5HT2A, CRHR1 and ACP1 variants in the risk of suicidal behavior.

LIMITATIONS

In our study we analyzed limited number of candidate genes and only one of them is linked to lithium mechanism of action. We had no data on pharmacological treatment of investigated patients and its relation to the time of suicide attempt.

CONCLUSION

Our results indicate that polymorphisms of various signaling pathways are involved in the pathogenesis of suicidal behavior. Non-genetic factors are also involved in the risk of suicidal attempts.

Genetic Association Studies of Suicidal Behavior: A Review of the Past 10 Years, Progress, Limitations, and Future Directions

Suicidal behaviors (SBs), which range from suicidal ideation to suicide attempts and completed suicide, represent a fatal dimension of mental ill-health. The involvement of genetic risk factors in SB is supported by family, twin, and adoption studies. The aim of this paper is to review recent genetic association studies in SBs including (i) case-control studies, (ii) family-based association studies, and (iii) genome-wide association studies (GWAS). Various studies on genetic associations have tended to suggest that a number of genes [e.g., tryptophan hydroxylase, serotonin receptors and transporters, or brain-derived neurotrophic factors (BDNFs)] are linked to SBs, but these findings are not consistently supported by the results obtained. Although the candidate-gene approach is useful, it is hampered by the present state of knowledge concerning the pathophysiology of diseases. Interpretations of GWAS results are mostly hindered by a lack of annotation describing the functions of most variation throughout the genome. Association studies have addressed a wide range of single-nucleotide polymorphisms in numerous genes. We have included 104 such studies, of which 10 are family-based association studies and 11 are GWAS. Numerous meta-analyses of case-control studies have shown significant associations of SB with variants in the serotonin transporter gene (5-HTT or SLC6A4) and the tryptophan hydroxylase 1 gene (TPH1), but others report contradictory results. The gene encoding BDNF and its receptor (NTRK2) are also promising candidates. Only two of the GWAS showed any significant associations. Several pathways are mentioned in an attempt to understand the lack of reproducibility and the disappointing results. Consequently, we review and discuss here the following aspects: (i) sample characteristics and confounding factors; (ii) statistical limits; (iii) gene-gene interactions; (iv) gene, environment, and by time interactions; and (v) technological and theoretical limits.

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.

Integrated theory to unify status among schizophrenia and manic depressive illness

Tryptophan hydroxylase 1 is primarily expressed in the gastrointestinal tract, and has been associated with both schizophrenia and depression. Although decreased serotonin activity has been reported in both depression and mania, it is important to investigate the interaction between serotonin and other neurotransmitter systems. There are competitive relationships between branched-chain amino acids, and tryptophan and tyrosine that relate to physical activity, and between L-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP), both highly dependent on intracellular tetrahydrobiopterin concentrations. Here, I propose a chaos theory for schizophrenia, mania, and depression using the competitive interaction between tryptophan and tyrosine with regard to the blood-brain barrier and coenzyme tetrahydrobiopterin. Mania may be due to the initial conditions of physical hyperactivity and hypofunctional 5-HTP-producing cells inducing increased dopamine. Depression may be due to the initial conditions of physical hypoactivity and hypofunctional 5-HTP-producing cells inducing decreased serotonin. Psychomotor excitation may be due to the initial conditions of physical hyperactivity and hyperfunctional 5-HTP-producing cells inducing increased serotonin and substantially increased dopamine. The hallucinatory-paranoid state may be due to the initial conditions of physical hypoactivity and hyperfunctional 5-HTP-producing cells inducing increased serotonin and dopamine.

Association analysis of TPH-1 and TPH-2 genes with suicidal behavior in patients with attempted suicide in Mexican population

BACKGROUND

Suicidal behavior is a worldwide health problem. Tryptophan hydroxylase (TPH) is a rate limiting enzyme in the biosynthesis of serotonergic neurotransmission. TPH-1 and TPH-2 genes encode for TPH isoforms and have been implicated as candidate genes for suicidal behavior. The aim of this study was to evaluate the association between the genetic variants of the TPH-1 (rs21102 and 1607395) and TPH-2 (rs4290270, rs7305115 and rs1007023) genes and suicidal behavior in a Mexican population.

METHODS

We conducted a case-control study including 200 cases with suicide attempt and 263 controls. Patients were evaluated by a trained psychiatrist or clinical psychologists. Five polymorphisms were genotyped and assessed for allele, genotype and haplotype association with suicide attempt.

RESULTS

The rs7305115 polymorphism of the TPH-2 gene was associated with suicidal behavior in a Mexican population in genotype (χ(2)=6.02, df=2, p=0.04) and allele (OR=1.39, 95%IC=1.06-1.81, p=0.01) frequencies. The THP-2 haplotypes GTA (χ(2)=5.68, p=0.01) and ATT (χ(2)=5.0, p=0.02) were associated with risk for suicide attempt.

CONCLUSION

Our results provide evidence for an association between the rs7305115 polymorphism of the TPH-2 gene and suicidal behavior in a Mexican population. However, more studies are necessary to replicate these results using larger samples.

Specific and common genes implicated across major mental disorders: a review of meta-analysis studies

Major efforts have been directed at family-based association and case-control studies to identify the involvement of candidate genes in the major disorders of mental health. What remains unknown is whether candidate genes are associated with multiple disorders via pleiotropic mechanisms, and/or if other genes are specific to susceptibility for individual disorders. Here we undertook a review of genes that have been identified in prior meta-analyses examining specific genes and specific mental disorders that have core disruptions to emotional and cognitive function and contribute most to burden of illness- major depressive disorder (MDD), anxiety disorders (AD, including panic disorder and obsessive compulsive disorder), schizophrenia (SZ) and bipolar disorder (BD) and attention deficit hyperactivity disorder (ADHD). A literature review was conducted up to end-March 2013 which included a total of 1519 meta-analyses across 157 studies reporting multiple genes implicated in one or more of the five disorders studied. A total of 134 genes (206 variants) were identified as significantly associated risk variants for MDD, AD, ADHD, SZ or BD. Null genetic effects were also reported for 195 genes (426 variants). 13 genetic variants were shared in common between two or more disorders (APOE e4, ACE Ins/Del, BDNF Val66Met, COMT Val158Met, DAOA G72/G30 rs3918342, DAT1 40-bp, DRD4 48-bp, SLC6A4 5-HTTLPR, HTR1A C1019G, MTHR C677T, MTHR A1298C, SLC6A4 VNTR and TPH1 218A/C) demonstrating evidence for pleiotrophy. Another 12 meta-analyses of GWAS studies of the same disorders were identified, with no overlap in genetic variants reported. This review highlights the progress that is being made in identifying shared and unique genetic mechanisms that contribute to the risk of developing several major psychiatric disorders, and identifies further steps for progress.

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.

Genetic association studies between SNPs and suicidal behavior: a meta-analytical field synopsis

The large number of published meta-analyses on the associations between single-nucleotide polymorphisms (SNPs) and suicidal behavior mirrors the enormous research interest in this topic. Although meta-analytic evidence is abundant and certain patterns are apparent, those have not been integrated into a general framework as of yet. In a systematic review, genetic association studies between SNPs and suicidal behavior were identified. Previously published meta-analyses for eight SNPs were updated and the results of the different meta-analyses were compared. Meta-analyses for 15 SNPs, which had not been subjected to meta-analysis before, were conducted. The present meta-analytical field synopsis showed five major similarities between new and published analyses: 1) Summary effect sizes were small and rarely statistically significant, 2) heterogeneity between studies was often substantial, 3) there were no time trends, 4) effects were easily swayed and were largely dependent on individual studies, and 5) publication bias does not play a role in this field of research. Meta-analytic data show once more that major contributions of single genes are unlikely. However, association studies and corresponding meta-analyses have been an important and necessary stepping stone in the development of modern and more complex approaches in the genetics of suicidal behavior.

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.

An association study of suicide and candidate genes in the serotonergic system

INTRODUCTION

Strong evidence demonstrates a genetic susceptibility to suicidal behaviour and a relationship between suicide and mental disorders. The aim of this study was to test for association between suicide and five selected genetic variants, which had shown association with suicide in other populations.

METHOD

We performed a nationwide case-control study on all suicide cases sent for autopsy in Denmark between the years 2000 and 2007. The study comprised 572 cases and 1049 controls and is one of the largest genetic studies in completed suicide to date. The analysed markers were located within the Serotonin Transporter (SLC6A4), Monoamine Oxidase-A (MAOA) and the Tryptophan Hydroxylase I and II (TPH1 and TPH2) genes.

RESULTS

None of the genetic markers within SLC6A4, MAOA, TPH1 and TPH2 were significantly associated with completed suicide or suicide method in the basic association tests. Exploratory interaction test showed that the minor allele of rs1800532 in TPH1 has a protective effect for males younger than 35 years and females older than 50 years, whereas for the oldest male subjects, it tended to be a risk factor. We also observed a significant interaction between age-group and the 5-HTTLPR genotype (with and without rs25531) in SLC6A4. The long allele or high expression allele tends to have a protective effect in the middle age-group.

LIMITATION

We only analysed a limited number of genetic variants.

CONCLUSION

None of the analysed variants are strong risk factors. To reveal a better understanding of the genes involved in suicide, we suggest future studies should include both genetic and non-genetic factors.

Novel molecular changes induced by Nrg1 hypomorphism and Nrg1-cannabinoid interaction in adolescence: a hippocampal proteomic study in mice

Neuregulin 1 (NRG1) is linked to an increased risk of developing schizophrenia and cannabis dependence. Mice that are hypomorphic for Nrg1 (Nrg1 HET mice) display schizophrenia-relevant behavioral phenotypes and aberrant expression of serotonin and glutamate receptors. Nrg1 HET mice also display idiosyncratic responses to the main psychoactive constituent of cannabis, Δ⁹-tetrahydrocannabinol (THC). To gain traction on the molecular pathways disrupted by Nrg1 hypomorphism and Nrg1-cannabinoid interactions we conducted a proteomic study. Adolescent wildtype (WT) and Nrg1 HET mice were exposed to repeated injections of vehicle or THC and their hippocampi were submitted to 2D gel proteomics. Comparison of WT and Nrg1 HET mice identified proteins linked to molecular changes in schizophrenia that have not been previously associated with Nrg1. These proteins are involved in vesicular release of neurotransmitters such as SNARE proteins; enzymes impacting serotonergic neurotransmission, and proteins affecting growth factor expression. Nrg1 HET mice treated with THC expressed a distinct protein expression signature compared to WT mice. Replicating prior findings, THC caused proteomic changes in WT mice suggestive of greater oxidative stress and neurodegeneration. We have previously observed that THC selectively increased hippocampal NMDA receptor binding of adolescent Nrg1 HET mice. Here we observed outcomes consistent with heightened NMDA-mediated glutamatergic neurotransmission. This included differential expression of proteins involved in NMDA receptor trafficking to the synaptic membrane; lipid raft stabilization of synaptic NMDA receptors; and homeostatic responses to dampen excitotoxicity. These findings uncover novel proteins altered in response to Nrg1 hypomorphism and Nrg1-cannabinoid interactions that improves our molecular understanding of Nrg1 signaling and Nrg1-mediated genetic vulnerability to the neurobehavioral effects of cannabinoids.

Analysis of four genes involved in the neurodevelopment shows association of rs4307059 polymorphism in the cadherin 9/10 region with completed suicide

BACKGROUND

We hypothesized that DNA variants affecting neurodevelopment such as rs4307059 (CDH10/CDH9), rs930752 (NRXN1), rs6265 (BDNF) or rs10868235 (NTRK2) may predispose to completed suicide.

METHODOLOGY

We used a case-control two-stage approach based on a discovery cohort (557 cases and ∼550 controls) and replication cohort (159 cases and 186 controls). The suicides were ascertained as consecutive cases autopsied at the Department of Forensic Medicine, Medical University of Warsaw, Poland.

RESULTS

In the discovery cohort we found an association between suicide and the CC genotype in the rs4307059 polymorphism (OR 1.64, p = 0.012). The trend for an overrepresentation of the CC homozygotes among suicides was replicated in the second cohort (OR 1.97, p = 0.056). Analysis in the pooled cohorts showed that rs4307059 CC was associated with completed suicide (OR 1.71, p = 0.002) also after Bonferroni correction (p(cor.) = 0.024). In an exploratory search for genotype-phenotype correlation we found that males with the rs4307059 CC genotype committed suicide earlier than those with CT/TT genotypes (p = 0.049).

CONCLUSIONS

The CC genotype of rs4307059 located in the region between CDH9 and CDH10 is associated with completed suicide in a Polish cohort.

The role of the serotonergic system in suicidal behavior

Serotonin is a widely investigated neurotransmitter in several psychopathologies, including suicidal behavior (SB); however, its role extends to several physiological functions involving the nervous system, as well as the gastrointestinal and cardiovascular systems. This review summarizes recent research into ten serotonergic genes related to SB. These genes - TPH1, TPH2, SLC6A4, SLC18A2, HTR1A, HTR1B, HTR2A, DDC, MAOA, and MAOB - encode proteins that are vital to serotonergic function: tryptophan hydroxylase; the serotonin transporter 5-HTT; the vesicular transporter VMAT2; the HTR1A, HTR1B, and HTR2A receptors; the L-amino acid decarboxylase; and the monoamine oxidases. This review employed a systematic search strategy and a narrative research methodology to disseminate the current literature investigating the link between SB and serotonin.

Neurocognitive function in long-term treated schizophrenia: a five-year follow-up study

Neurocognitive deficits are a core feature of schizophrenia. Deficits covering a wide range of functions have been well documented. However there is still a lack of longitudinal studies regarding the development of neurocognitive impairment. The current study examined the effect of time in long-term treated patients with schizophrenia and healthy controls on cognitive functions. A neurocognitive test-battery was administered to 36 patients and 46 controls on two occasions with approximately 4.5 years interval. Patients performed significantly worse on all measures on both occasions. The only significant decline over time was the ability to shift mental set between different rules or categories (measured by Trail Making Test B). This decline was present in both patients and controls. Improvement on attention (tested by Continuous Performance Test) was found in patients only and improvement on verbal learning (tested by Rey Auditory Verbal Learning Test) was found only in controls. Education was significantly related to outcome in patients and age was related to outcome in controls. We conclude that neurocognitive function is relatively stable over 4.5 years in patients with long-term treated schizophrenia, in line with previous scientific research. The authors discuss the impact of age and education and limitations of the study.

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.

Investigation of tryptophan hydroxylase 2 (TPH2) in schizophrenia and in the response to antipsychotics

Serotonergic transmission is considered relevant in the pathophysiology and the treatment of schizophrenia. Tryptophan hydroxylase (TPH) is the rate limiting enzyme in the biosynthesis of serotonin. While the TPH1 gene has been found to be associated with schizophrenia, studies focusing on TPH2 variants did not yield conclusive results for schizophrenia or the response to antipsychotic medication. We analyzed eleven TPH2 SNPs in two case-control samples consisting of 4453 individuals in total. Six SNPs were selected because of their potential functional relevance (rs4570625, rs11178997, rs11178998, rs7954758, rs7305115, and, rs4290270) and were supported by another 5 tagging SNPs selected based on HapMap LD information. In the discovery sample (1476 individuals), we observed a significant association with schizophrenia for rs10784941 (p = 0.009, OR minor G-allele 0.82 [0.71-0.95]) and rs4565946 (p = 0.011, OR minor T-allele 0.83 [0.71-0.96]). Association was also observed with a common rs4570625-rs4565946 haplotype (OR G-C haplotype 1.20 [1.02-1.40]; p = 0.0046). Single-marker associations could not be replicated in the replication sample consisting of 2977 individuals, but there was a strong trend regarding the rs4570625-rs4565946 G-C haplotype (OR 1.10 [0.98-1.24]; p(one-sided test) = 0.054). In smaller sub-samples, the rare rs4570625-rs4565946 T-T haplotype was associated with reduced processing speed (n = 193, p = 0.004) and sensorimotor gating (n = 68, p = 0.006) of schizophrenia patients. TPH2 variants and the rs4570625-rs4565946 G-C haplotype did not influence the beneficial response to antipsychotic drugs (n = 210) after four weeks of treatment administering the Positive and Negative Syndrome Scale of Schizophrenia (PANSS). We also investigated the association of the SNPs to treatment response, but did not get significant results. In sum, our results argue for only a minor role of TPH2 in schizophrenia.

Association between a genetic variant in the serotonin transporter gene (SLC6A4) and suicidal behavior in patients with schizophrenia

Background

The serotonin (5-hydroxytryptamin; 5-HT) system has a central role in the circuitry of cognition and emotions. Multiple lines of evidence suggest that genetic variation in the serotonin transporter gene (SLC6A4; 5-HTT) is associated with schizophrenia and suicidal behavior. In this study, we wanted to elucidate whether SLC6A4 variations is involved in attempted suicide among patients with schizophrenia in a Scandinavian case–control sample.

Methods

Patients diagnosed with schizophrenia from three Scandinavian samples were assessed for presence or absence of suicide attempts, based on record reviews and interview data. Seven SLC6A4 single nucleotide polymorphisms (SNPs) were genotyped in 837 schizophrenia patients and 1,473 control individuals. Association analyses and statistical evaluations were performed with the program UNPHASED (version 3.0.9).

Results

We observed an allele association between the SNP rs16965628, located in intron one of SLC6A4, and attempted suicide (adjusted p-value 0.01), among patients with schizophrenia. No association was found to a diagnosis of schizophrenia, when patients were compared to healthy control individuals.

Conclusion

The gene SLC6A4 appears to be involved in suicidal ideation among patients with schizophrenia. Independent replication is needed before more firm conclusions can be drawn.

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.

Use of antipsychotics - an analysis of lifetime treatment in 66 patients with psychoses

Only a minority of patients treated with antipsychotics in clinical studies continue their treatments throughout a longer study period. Few studies address this issue from a lifetime perspective. In this naturalistic study, we aimed at analysing the prescription pattern of antipsychotic drugs among a sample of Swedish patients with a diagnosis of psychotic illness, from the first contact with psychiatry (typically between 1973 and 1997) until the last written note in the case history documents. A retrospective descriptive analysis was performed of all case history data of 66 patients diagnosed with schizophrenia or related psychotic disorders. Patients with schizophrenia were prescribed antipsychotic medication more than 90% of the time. Each patient generally had been prescribed several (up to 16) different antipsychotic drugs and a quarter of the patients had been prescribed two or more antipsychotics for a third of their prescription time. Patients with psychosis were exposed to a cumulatively growing number of antipsychotics. Various factors, including clinician and patient expectations, and specific strengths and limitations of available antipsychotics may account for frequent medication changes over time.

Brain serotonergic circuitries

Brain serotonergic circuitries interact with other neurotransmitter systems on a multitude of different molecular levels. In humans, as in other mammalian species, serotonin (5-HT) plays a modulatory role in almost every physiological function. Furthermore, serotonergic dysfunction is thought to be implicated in several psychiatric and neurodegenerative disorders. We describe the neuroanatomy and neurochemistry of brain serotonergic circuitries. The contribution of emergent in vivo imaging methods to the regional localization of binding site receptors and certain aspects of their functional connectivity in correlation to behavior is also discussed. 5-HT cell bodies, mainly localized in the raphe nuclei, send axons to almost every brain region. It is argued that the specificity of the local chemocommunication between 5-HT and other neuronal elements mainly depends on mechanisms regulating the extracellular concentration of 5-HT the diversity of high-affinity membrane receptors, and their specific transduction modalities.

Associations of tryptophan hydroxylase gene polymorphisms with irritable bowel syndrome

BACKGROUND

Alterations in serotonin (5-HT) are suspected in the pathophysiology of irritable bowel syndrome (IBS). Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin and has two isoforms: TPH1 and TPH2. Genetic variants in both genes have been studied in various disorders related to serotonin dysregulation. The aim of this study was to examine whether TPH gene variants were associated with IBS and IBS-related gastrointestinal (GI) symptoms.

METHODS

Five single nucleotide polymorphisms (SNPs) from the TPH1 and one SNP from the TPH2 were genotyped in 199 IBS patients and 79 healthy controls. All subjects were Caucasian women of European origin. Irritable bowel syndrome patients filled in a daily diary with five GI symptoms and stool characteristics for 28 days.

KEY RESULTS

The TPH1 SNPs showed no association with the diagnosis of IBS. However, among IBS patients, all five TPH1 SNPs showed some association with diarrhea and loose type of stool consistency, with P-values rating from 0.01 to 0.20. The TPH2 SNP showed a trend towards a reduced risk of IBS and possible associations with stool characteristics, both hard and loose stools. However, no P-values were less than the conservative multiple-comparison-adjusted threshold of 0.001 and hence these results must be interpreted cautiously.

CONCLUSIONS & INFERENCES

This study is the first to assess associations of TPH gene variants with IBS-related GI symptoms and stool characteristics. The possible association of TPH gene variants with diarrhea needs to be verified in an independent sample.

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.

Suicide in schizophrenia

Schizophrenia is a disorder with an estimated suicide risk of 4-5%. Many factors are involved in the suicidal process, some of which are different from those in the general population. Clinical risk factors include attempted suicide, depression, male gender, substance abuse and hopelessness. Biosocial factors, such as a high intelligence quotient and high level of premorbid function, have also been associated with an increased risk of suicide in patients with schizophrenia. Suicide risk is especially high during the first year after diagnosis. Many of the suicides occur during hospital admission or soon after discharge. Management of suicide risk includes both medical treatment and psychosocial interventions. Still, risk factors are crude; efforts to predict individual suicides have not proved useful and more research is needed.

TPH1 218A/C polymorphism is associated with major depressive disorder and its treatment response

The association between the tryptophan hydroxylase 1 (TPH1) 218A/C polymorphism and (1) severity of major depressive disorder (MDD) and (2) response to treatment was studied. There were three study populations, the first consisting of 119 treatment-resistant MDD inpatients treated with electro-convulsive therapy (ECT), and the second of 98 MDD open care patients treated with selective serotonin reuptake inhibitors (SSRI). In addition, there was a control population of 395 healthy blood donors. The first aim of the study was to compare the genotypes of the patient with those of the healthy controls and between patient populations. The second aim was to compare the genotypes of MDD patients achieving remission with basic SSRI treatment (MADRS<8) with the genotypes of non-responders to ECT (defined as MADRS>15). TPH1 218A/C polymorphism was associated with the risk of MDD. CC genotype was significantly more common in patients (including both ECT and SSRI treated patients) than in controls (38.2% and 26.8% respectively; p=0.008), and its frequency was significantly higher in more severe forms of depression, i.e. in ECT treated patients compared with SSRI treated patients (42.0% and 33.7%, p=0.026). CC genotype was also associated with lower probability of achieving remission. It was significantly more frequent among ECT non-responders than among SSRI remitters (53.1% and 23.3%, p=0.049). In this Finnish population TPH1 218A/C polymorphism was associated with the risk of MDD and treatment response; CC genotype was associated with the increased risk of MDD and lower probability of responding treatment. Further studies with larger samples will be required to confirm the results.