No association between the tryptophan hydroxylase gene polymorphism and major depressive disorders and antidepressant response in a Korean population

The serotonergic neurotransmitter system has been implicated in major depressive disorder (MDD) and appears to be the target of a variety of antidepressants. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin biosynthesis, and selective serotonin re-uptake inhibitors exert their activity enhancing the general serotonergic tone. The goal of this study was to investigate whether the A218C polymorphism of the TPH gene is associated with MDD or antidepressant response. All patients were evaluated at the start and in the eighth week of using the 21-item Hamilton Depression Rating Scale. Genotyping was analyzed with polymerase chain reaction. There were no significant differences in genotypes and allele frequencies between the MDD patients (n = 93) and the control group (n = 127) and in the antidepressant response among TPH gene variants. Results suggest that the A218C polymorphism of the TPH gene does not play a major role in pathogenesis in MDD and does not serve as a modulator of antidepressant activity.     

Tryptophan hydroxylase gene polymorphisms are not associated with suicide

Several lines of evidence suggest a serotonergic dysfunction involved in the biological susceptibility of suicide. Abnormalities of serotonergic markers such as 5-hydroxyindoleacetic acid and prolactin response to fenfluramine have been demonstrated in suicide subjects. 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 and some of these polymorphisms have been suggested to be associated with suicide, but the results are still inconsistent. We examined whether the -6526A/G polymorphism in the promoter region and the 218A/C polymorphism in intron 7 of the TPH gene were associated with suicide using 132 Japanese suicide victims. No significant difference in genotype distribution and allele frequencies of these polymorphisms was found between the suicide victims and the controls. We concluded neither the -6526A/G polymorphism nor the 218A/C polymorphism of the TPH gene is likely to have a major effect on the susceptibility of suicide. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:861-863, 2000.     

A dimensional impulsive-aggressive phenotype is associated with the A218C polymorphism of the tryptophan hydroxylase gene: a pilot study in well-characterized impulsive inpatients

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of serotonin, and association and linkage studies of its variants in suicidal and impulsive-aggressive behavior have brought conflicting results. This pilot study was designed to investigate whether TPH A218C genotypes could be associated with impulsive behavioral tendencies (IBTs) in consecutively admitted nonpsychotic nonorganic inpatients. Patients (20 females and 34 males; age, 38.8 +/- 11.8) did not differ from healthy nonimpulsive controls (16 females and 11 males; age, 35.2 +/- 10.2) regarding TPH genotypes, but in the patients, the number of IBT was related to the presence of the 218C allele. It was concluded that impulsive-aggressive behavior may be associated with the TPH genotype in well-characterized impulsive patients and that the present results stress the importance of considering impulsiveness-aggressiveness in studies investigating the relationship between suicidal behavior and TPH genotypes.     

TPH2基因单核苷酸多态性与单相抑郁及其自杀行为的关系

目的探讨色氨酸羟化酶2(TPH2)基因rs7305115单核苷酸多态性与单相抑郁及自杀行为的关系。方法提取197例单相抑郁患者和225名健康对照者基因组DNA,采用聚合酶链反应(polymerase chain reaction PCR)扩增包括TPH2基因rs7305115位点的312bp基因组DNA片段及PCR产物直接测序。结果在第7外显子周围未发现其它的单核苷酸多态性。单相抑郁患者和健康对照者TPH2 rs7305115基因型和等位基因频率无统计学意义的差别(P>0.05),但患者组内有自杀行为的个体携带基因型AA的频率及等位基因A的频率均较低,两组比较差异有统计学意义(P<0.05)。结论TPH2基因rs7305115单核苷酸多态性与单相抑郁无明显关联,与自杀行为有关联。其可能与抑郁症自杀行为易感性相关。     

Lack of association between the tryptophan hydroxylase gene A218C polymorphism and attention-deficit hyperactivity disorder in Chinese Han population

Previous studies have suggested that the serotonergic (5-HT) system might be involved in the development of Attention-deficit hyperactivity disorder (ADHD). ADHD is frequently characterized by aggressive and impulsive behavior, a major symptom associated with reduction in serotonergic function. The tryptophan hydroxylase (TPH) gene is a reasonable candidate for ADHD because it encodes the rate-limiting enzyme in the process of 5-HT biosynthesis. In this study, we examined the relationship between the A218C polymorphism in TPH gene and ADHD. Sixty-nine ADHD patients and their biological parents were investigated. The A218C polymorphism in intron 7 of TPH gene was detected by PCR-RFLP method. No allele or genotype concerned with this A218C polymorphism was found to be associated with ADHD when analyzed with the haplotype relative risk method. Therefore, our data indicate that the TPH gene A218C polymorphism may not be a susceptibility factor of ADHD in the Chinese Han population.     

Lack of association between the tryptophan hydroxylase gene A218C polymorphism and attention‐deficit hyperactivity disorder in Chinese Han population

Previous studies have suggested that the serotonergic (5‐HT) system might be involved in the development of Attention‐deficit hyperactivity disorder (ADHD). ADHD is frequently characterized by aggressive and impulsive behavior, a major symptom associated with reduction in serotonergic function. The tryptophan hydroxylase (TPH) gene is a reasonable candidate for ADHD because it encodes the rate‐limiting enzyme in the process of 5‐HT biosynthesis. In this study, we examined the relationship between the A218C polymorphism in TPH gene and ADHD. Sixty‐nine ADHD patients and their biological parents were investigated. The A218C polymorphism in intron 7 of TPH gene was detected by PCR‐RFLP method. No allele or genotype concerned with this A218C polymorphism was found to be associated with ADHD when analyzed with the haplotype relative risk method. Therefore, our data indicate that the TPH gene A218C polymorphism may not be a susceptibility factor of ADHD in the Chinese Han population. © 2001 Wiley‐Liss, Inc.     

TPH2基因单核苷酸多态性与双相情感障碍及其自杀行为的关系

目的 探讨色氨酸羟化酶2(TPH2)基因rs7305115单核苷酸多态性与双相情感障碍及自杀行为的关系.方法 提取205例双相情感障碍患者和225名健康对照者基因组DNA,采用聚合酶链反应(polymerase chain reaction PCR)扩增包括TPH2基因rs7305115位点的312bp基因组DNA片段,PCR产物直接测序.结果 在第7外显子周围未发现其它的单核苷酸多态性.双相情感障碍患者和健康对照者TPH2 rs7305115基因型和等位基因频率无统计学意义的差别(P>0.05),但患者组内有自杀行为的个体携带基因型AA的频率及等位基因A的频率均较低,两组比较差异有统计学意义(P<0.05).结论 TPH2基因rs7305115单核苷酸多态性与双相情感障碍无明显关联,与自杀行为有关联,其可能与双相情感障碍自杀行为易感性相关.

Abstract：

Objective To explore the relation among single nucleotide polymorphism of a novel tryptophan hydroxylase isoform (TPH2) gene rs7305115,bipolar disorder and suicidal behavior. Methods Specimens of peripheral blood were collected from 205 bipolar disorder and 225 controls. A novel tryptophan hydroxylase isoform (TPH2) gene rs7305115 in length 312bp was amplitied by Polvmerase chain reaction (PCR), and the product was analyzed by direct sequencing. Results We did not discover new single nucleotide polymorphism. Compared with Control Group,no significant difference of genotypes and alleles of TPH2 gene rs7305115 single nucleotide polymorphism had been found in patient group(P>0. 05). However,there existed significant differences between suicide behavior and non suicide behavior in bipolar disorder patient in genotypea of TPH2 gene rs7305115A/A. Suicide behavior of bipolar disorder patients in AA genotypes was much lower than non suicide behavior of bipolar disorder patients (P<0. 05). Con-clusion TPH2 gene rs7305115 single nucleotide polymorphism may have no association with the susceptibility of bipolar disorder, but associated with suicide behavior in bipolar disorder. A allele may be one of the risk factors for suicide behavior in bipolar disor-der.     

A dimensional impulsive‐aggressive phenotype is associated with the A218C polymorphism of the tryptophan hydroxylase gene: A pilot study in well‐characterized impulsive inpatients

Tryptophan hydroxylase (TPH) is the rate‐limiting enzyme in the biosynthesis of serotonin, and association and linkage studies of its variants in suicidal and impulsive‐aggressive behavior have brought conflicting results. This pilot study was designed to investigate whether TPH A218C genotypes could be associated with impulsive behavioral tendencies (IBTs) in consecutively admitted nonpsychotic nonorganic inpatients. Patients (20 females and 34 males; age, 38.8 ± 11.8) did not differ from healthy nonimpulsive controls (16 females and 11 males; age, 35.2 ± 10.2) regarding TPH genotypes, but in the patients, the number of IBT was related to the presence of the 218C allele. It was concluded that impulsive‐aggressive behavior may be associated with the TPH genotype in well‐characterized impulsive patients and that the present results stress the importance of considering impulsiveness‐aggressiveness in studies investigating the relationship between suicidal behavior and TPH genotypes. © 2002 Wiley‐Liss, Inc.     

Association study of the tryptophan hydroxylase gene and bipolar affective disorder using family-based internal controls

The tryptophan hydroxylase (TPH) gene encodes for the rate-limiting enzyme of the serotonin metabolism and, therefore, has to be considered a major candidate for association studies in affective disorders. Recently, an association between this gene and bipolar affective disorder has been reported in a French population. We sought to replicate this finding in a German sample. Allele frequencies of a biallelic polymorphism (A218C) of the TPH gene were determined in 95 bipolar I patients and their parents. Preferential transmission of alleles from heterozygous parents to bipolar offspring was tested with the "transmission disequilibrium test" (TDT), which eliminates the contribution of population stratification to an association finding. Our sample yielded a power >90% to detect the originally reported effect. Neither allele 218A nor allele 218C were preferentially transmitted from heterozygous parents to bipolar offspring. Our results, therefore, do not support the hypothesis that the TPH gene is involved in the etiology of bipolar disorder.     

Tryptophan hydroxylase polymorphisms in suicide victims

Both environmental and genetic factors appear to contribute to the risk for suicide. The serotonergic system has been implicated in depression, impulsivity and suicidality. Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the synthesis of serotonin. Suicide has been associated with polymorphisms in intron 7 of the TPH gene. These alleles were studied in samples from 47 deceased Caucasian males as part of the Utah Youth Suicide Study. A 918 base pair fragment spanning the region of interest was amplified. The A218C polymorphism was visualized by restriction fragment length polymorphism (RFLP) and the A779C was sequenced. Neither A218C nor A779C appeared to be associated with suicide in this population. These results did not change when the sample was stratified by age (10-21 years, 22-31 years) or when violent suicides were selected. The complexity of the phenotype of suicide may reflect multiple biological and social etiologic factors, and poses a worthy challenge for genetic studies.     

Case control and family-based studies of tryptophan hydroxylase gene A218C polymorphism and suicidality in adolescents.

The association of suicidality with polymorphism A218C in intron 7 of tryptophan hydroxylase (TPH) gene remains controversial. The aim of this study was to use family-based methods to examine this association in adolescents in order to eliminate the difficulty of sampling a control group from the same ethnic population. Eighty-eight inpatient adolescents who recently attempted suicide were assessed by structured interview for detailed clinical history, diagnoses, suicide intent, suicide risk, impulsivity, aggression, and depression. DNA samples were collected from all subjects, from both biological parents of 40 subjects and from one parent of 9 subjects; TPH allele frequencies were calculated and tested for association to phenotype, stratified by severity, using the haplotype relative risk (HRR) and transmission disequilibrium test (TDT) methods (n = 49). The frequencies were also compared for all the Jewish subjects (n = 84) to the known frequencies of these alleles in healthy Jewish populations. There was no significant allelic association of A218C polymorphism with suicidal behavior or other phenotypic measures according to the HRR method (chi-square = 0.094; P = 0.76), the TDT (chi-square = 0.258; P = 0.61), or association analysis to known population frequencies (chi-square = 1.667, P = 0.19 for Ashkenazi, and chi-square = 0.810, P = 0.37 for non-Ashkenazi). Analysis of variance with the Scheffè test demonstrated a significant difference between CC and AA genotypes in suicide risk and depression among the patients (n = 88). The findings suggest that polymorphism A218C has no major relevance to the pathogenesis of adolescent suicidal behavior, but may have a subtle effect on some related phenotypes.     

No association between a TPH2 promoter polymorphism and mood disorders or monoamine turnover

BACKGROUND: Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in serotonin synthesis. TPH2 is a recently discovered isoform that is expressed predominantly in serotonin neurons. Associations are reported of TPH2 polymorphisms with MDD, bipolar disorder and suicidal behavior. This study examines a single nucleotide polymorphism in the putative promoter region of the TPH2 gene. METHODS: One hundred nine bipolar, 324 major depressive disorder, and 130 healthy volunteers were genotyped for the rs4131347 (-C8347G) promoter SNP. Association was assessed with diagnosis, suicide attempt status, severity of psychopathology and cerebrospinal fluid monoamine metabolite levels of 5-HIAA, HVA, and MHPG. General linear models and logistic regression tested the effect of genotype*childhood abuse interactions on psychopathology severity and suicide attempt. RESULTS: There was no association between genotype and either mood disorder, suicide attempt status, psychopathology severity or CSF monoamine metabolite levels. CONCLUSIONS: No association was detected between the rs4131347 (-C8347G) SNP in the promoter region of the TPH2 gene and mood disorders, suicidal behavior or monoamine function.     

Deliberate self-harm is associated with allelic variation in the tryptophan hydroxylase gene (TPH A779C), but not with polymorphisms in five other serotonergic genes

BACKGROUND: There is a heritable component to suicidal behaviour, encouraging the search for the associated risk alleles. Given the putative role of the 5-HT (5-hydroxytryptamine; serotonin) system in suicidal behaviour, serotonergic genes are leading candidates. In particular, several studies have reported an association with variants in the tryptophan hydroxylase (TPH) gene. METHOD: We studied six serotonergic gene polymorphisms in a well-characterized sample of 129 deliberate self-harm subjects and 329 comparison subjects. The polymorphisms were TPH (A779C), 5-HT transporter (5-HTT, LPR S/L), monoamine oxidase A (MAOA G941T), 5-HT1B receptor (HTR1B G861C), 5-HT2A receptor (HTR2A T102C), and 5-HT2C receptor (HTR2C Cys23Ser). Genotyping was done using polymerase chain reaction (PCR)-based assays. The primary analyses compared allele and genotype frequencies between cases and controls. There were a limited number of planned secondary analyses within the deliberate self-harm group. RESULTS: The TPH A779 allele was more common in deliberate self-harm subjects than in controls (OR 1.38, 95% CI 1.02-1.88; P = 0.03). None of the other polymorphisms was associated with deliberate self-harm. Within the deliberate self-harm group there were no associations with impulsivity, suicide risk, lifetime history of depression, or family history of deliberate self-harm. CONCLUSIONS: Our data extend the evidence that allelic variation in the TPH gene is a risk factor for deliberate self-harm. No evidence was found to implicate the other polymorphisms.     

Tryptophan hydroxylase 1 gene (TPH1) moderates the influence of social support on depressive symptoms in adults

BACKGROUND: Tryptophan hydroxylases (TPHs) are involved in the biosynthesis of serotonin and are therefore candidate genes for psychiatric disorders, including depression. We examined whether the common 218 A > C and 779 A > C polymorphisms in the tryptophan hydroxylase 1 gene (TPH1) moderated the association between perceived social support and sub-clinical depressive symptoms in adults. METHODS: The subjects were a randomly selected subsample (n=341) of individuals participating in the Cardiovascular Risk in Young Finns study, who had data on social support on one assessment time and depressive symptoms on two assessment times. Social support was assessed on the Perceived Social Support Scale Revised (PSSS-R) and depressive symptoms on a modified version of the Beck's Depression Inventory (BDI). RESULTS: We found that low social support predicted depressive symptoms more strongly in individuals carrying A alleles of the TPH1 than in others. The interaction effect was observed in a cross-sectional analysis and when predicting depressive symptoms over a four-year period. LIMITATIONS: We did not have data on TPH2, which has recently been identified as the primary TPH isomorphism affecting serotonin synthesis in the brain. CONCLUSIONS: TPH1 gene may be involved in the development of depressive symptoms by moderating the impact of depressogenic social influences.     

A Tryptophan Hydroxylase 2 Gene Polymorphism is Associated with Panic Disorder

Panic disorder (PD) is a complex and heterogeneous psychiatric condition. Dysfunction within the serotonergic system has been hypothesized to play an important role in PD. The novel brain-specific serotonin synthesizing enzyme, tryptophan hydroxylase 2 (TPH2), which represents the rate-limiting enzyme of serotonin production in the brain, may therefore be of particular importance in PD. We investigated the TPH2 703G/T SNP for association with PD. Patients with PD (n = 108), and control subjects (n = 247), were genotyped for rs4570625 (TPH2 703G/T). Male and female subjects were analyzed separately. The severity of their symptoms was measured using the Spielberger state-trait anxiety inventory (STAI), panic disorder severity scale (PDSS), anxiety sensitivity index (ASI), acute panic inventory (API), and Hamilton’s rating scale for depression (HAMD). The genotype and allele frequencies of the PD patients and controls were analyzed using χ ² statistics. There was a significant difference in the allele frequency in rs4570625 between the PD patients and normal controls. The T allele was significantly less frequent in the PD patients. We also found a significant association with rs4570625 in the female subgroup. There was no difference in symptom severity among the genotypes of this polymorphism. This result suggests that rs4570625 polymorphism may play a significant role in the pathogenesis of PD. Moreover, rs4570625 may have a gender-dependent effect on susceptibility to PD. Further studies are needed to replicate the association that we observed. Edited by Tatiana Foroud.     

Further evidence of a combined effect of SERTPR and TPH on SSRIs response in mood disorders.

We reported an independent association of the short variant of the serotonin transporter gene-linked polymorphic region (SERTPR) and tryptophan hydroxylase (TPH) genes with antidepressant response to selective serotonin reuptake inhibitors (SSRIs). The aim of the present study was to confirm the effect of the SERTPR and TPH gene variants on the SSRIs antidepressant activity in a new sample of major and bipolar depressives. Two hundred and twenty one inpatients (major depressives = 128, bipolar disorder = 93) were treated with SSRIs (fluvoxamine or paroxetine) for 6 weeks; the severity of depressive symptoms was weekly assessed with the Hamilton Rating Scale for Depression (HAMD). SERTPR and TPH variants were determined using PCR-based techniques, 220 subjects genotyped for SERTPR and 221 for TPH that were never included in previous studies. SERTPR*s/s variant association with a poor response to SSRI treatment was confirmed, even if with less significant P values (P = 0.034), independently from clinical variables; pooling the present sample with previous ones we observed a highly significant effect (P < 0.000001). TPH*A/A variants showed higher HAMD scores throughout the trial but with only a trend in the same direction of our previous study in terms of a worse response of A/A genotypes. Thus, the previous positive association was not fully replicated for TPH. The present independent replication confirms SERTPR variants as a liability factor for antidepressant efficacy while the TPH effect is not unequivocal.     

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.     

Case control and family‐based studies of tryptophan hydroxylase gene A218C polymorphism and suicidality in adolescents

The association of suicidality with polymorphism A218C in intron 7 of tryptophan hydroxylase (TPH) gene remains controversial. The aim of this study was to use family‐based methods to examine this association in adolescents in order to eliminate the difficulty of sampling a control group from the same ethnic population. Eighty‐eight inpatient adolescents who recently attempted suicide were assessed by structured interview for detailed clinical history, diagnoses, suicide intent, suicide risk, impulsivity, aggression, and depression. DNA samples were collected from all subjects, from both biological parents of 40 subjects and from one parent of 9 subjects; TPH allele frequencies were calculated and tested for association to phenotype, stratified by severity, using the haplotype relative risk (HRR) and transmission disequilibrium test (TDT) methods (n = 49). The frequencies were also compared for all the Jewish subjects (n = 84) to the known frequencies of these alleles in healthy Jewish populations. There was no significant allelic association of A218C polymorphism with suicidal behavior or other phenotypic measures according to the HRR method (chi‐square = 0.094; P = 0.76), the TDT (chi‐square = 0.258; P = 0.61), or association analysis to known population frequencies (chi‐square = 1.667, P = 0.19 for Ashkenazi, and chi‐square = 0.810, P = 0.37 for non‐Ashkenazi). Analysis of variance with the Scheffè test demonstrated a significant difference between CC and AA genotypes in suicide risk and depression among the patients (n = 88). The findings suggest that polymorphism A218C has no major relevance to the pathogenesis of adolescent suicidal behavior, but may have a subtle effect on some related phenotypes. © 2001 Wiley‐Liss, Inc.     

Variation in tryptophan hydroxylase-2 gene is not associated to male completed suicide in Estonian population

Dysfunction of the central serotonergic system has been related to a spectrum of psychiatric disorders, including suicidal behavior. Tryptophan hydroxylase isoform 2 (TPH2) is the rate-limiting enzyme in the biosynthetic pathway of serotonin, being expressed in serotonergic neurons of raphe nuclei. We investigated genetic variation in TPH2 gene in two samples of male subjects: 288 suicide completers and 327 volunteers, in order to reveal any associations between 14 single nucleotide polymorphisms and completed suicide. No associations were revealed neither on allelic nor haplotype level. Our finding does not support the hypothesis of TPH2 being a susceptibility factor for completed suicide in males of Estonian origin.