Genetic TPH2 variants and the susceptibility for migraine: association of a TPH2 haplotype with migraine without aura

The serotonergic system plays a major role in the etiology of migraine. The rate-limiting enzyme in serotonin homeostasis and availability is tryptophan hydroxylase (TPH). The TPH2 isoform is responsible for the cerebral serotonin biosynthesis. To investigate the role of genetic variation in TPH2 in the pathogenesis of migraine eight haplotype tagging SNPs covering the whole TPH2 gene where chosen using Haploview and genotyped in 503 migraineurs and 515 healthy controls. Association analysis was performed on a single SNP and haplotype basis using χ ² and logistic regression analysis. Single SNP analysis revealed a weak association with migraine, which did not remain after correction for multiple testing. Haplotype analyses revealed association of a haplotype with migraine without aura. Stratification by aura and triptan response did not reveal a positive association with the investigated polymorphisms. These results suggest a possible influence of genetic variation in TPH2 in the pathogenesis of migraine.     

Tryptophan hydroxylase gene and major psychoses

Disturbances of the serotoninergic neurotransmitter system have been implicated in the pathogenesis of mood disorders. The tryptophan hydroxylase (TPH) gene, which codes for the rate-limiting enzyme of serotonin biosynthesis, has been recently reported to be associated with bipolar disorder. In this study, we investigated TPH A218C gene variants in a sample of subjects affected by major psychoses. One thousand four hundred and twenty-four inpatients affected by bipolar (n=627), major depressive (n=511), schizophrenic (n=210), delusional (n=48) disorder and psychotic disorder not otherwise specified (n=27) (DSM-IV) were included; all patients and 380 controls were typed for the TPH variants using PCR techniques. A sub-sample of 963 patients was assessed using the Operational Criteria for Psychotic Illness (OPCRIT). TPH variants were not associated with major psychoses, but a trend was observed toward an excess of TPH*A/A in bipolar disorder. The analysis of symptomatology factors did not show any significant difference either; however, a trend was observed for males with the TPH*A genotype to have lower depressive symptoms compared with TPH*C subjects. Possible stratification factors such as current age and age of onset did not affect the observed results. TPH A218C variants are not, therefore, a major liability factor for the symptoms of major psychoses to have in the present sample. TPH*A containing variants may be a protective factor for depressive symptoms among male subjects with mood disorders or for a subtype of mood disorders characterized by a mainly manic form of symptomatology.     

A functional Tph2 C1473G polymorphism causes an anxiety phenotype via compensatory changes in the serotonergic system

The association of single-nucleotide polymorphisms (SNPs) in the human tryptophan hydroxylase 2 (TPH2) gene with anxiety traits and depression has been inconclusive. Observed inconsistencies might result from the fact that TPH2 polymorphisms have been studied in a genetically heterogeneous human population. A defined genetic background, control over environmental factors, and the ability to analyze the molecular and neurochemical consequences of introduced genetic alterations constitute major advantages of investigating SNPs in inbred laboratory mouse strains. To investigate the behavioral and neurochemical consequences of a functional C1473G SNP in the mouse Tph2 gene, we generated congenic C57BL/6N mice homozygous for the Tph2 1473G allele. The Arg(447) substitution in the TPH2 enzyme resulted in a significant reduction of the brain serotonin (5-HT) in vivo synthesis rate. Despite decreased 5-HT synthesis, we could detect neither a reduction of brain region-specific 5-HT concentrations nor changes in baseline and stress-induced 5-HT release using a microdialysis approach. However, using a [(35)S]GTP-γ-S binding assay and 5-HT(1A) receptor autoradiography, a functional desensitization of 5-HT(1A) autoreceptors could be identified. Furthermore, behavioral analysis revealed a distinct anxiety phenotype in homozygous Tph2 1473G mice, which could be reversed with chronic escitalopram treatment. Alterations in depressive-like behavior could not be detected under baseline conditions or after chronic mild stress. These findings provide evidence for an involvement of functional Tph2 polymorphisms in anxiety-related behaviors, which are likely not caused directly by alterations in 5-HT content or release but are rather due to compensatory changes during development involving functional desensitization of 5-HT(1A) autoreceptors.     

Monoamine oxidase: A gene polymorphism,tryptophan hydroxylase gene polymorphism and antidepressant response to fluvoxamine in Japanese patients with major depressive disorder

Monoamine oxidase A (MAOA) and tryptophan hydroxylase (TPH) are the staple enzymes in the metabolism of serotonin (5-HT). The genetic polymorphisms of these two enzymes might individually alter the production, release, reuptake or degradation of 5-HT during the treatment of selective serotonin reuptake inhibitors (SSRIs), leading to the individual differences in the antidepressant effects of SSRIs. The authors investigated whether a functional polymorphism in the MAOA gene promoter (MAOA-VNTR) and a TPH gene polymorphism in intron 7 (TPH-A218C) were associated with the antidepressant response to fluvoxamine in 66 Japanese patients with major depressive disorder during a 6-week study with a specific dosage plan. Fifty-four patients completed the study. The present study fails to demonstrate that the genetic polymorphisms of MAOA-VNTR and TPH-A218C affect the antidepressant effect of fluvoxamine in Japanese patients with major depressive disorder.     

Influence of 5-HTTLPR and TPH variants on illness time course in mood disorders

The aim of our study was to investigate gene variants in the long-term outcome of mood disorders. We retrospectively studied a sample of inpatients affected by recurrent and rapid cycling mood disorders. The serotonin transporter gene-linked functional polymorphic region (5-HTTLPR) and the A218C tryptophan hydroxylase (TPH) gene variant were determined using a PCR-based technique. For 5-HTTLPR polymorphism we genotyped 435 inpatients affected by major depressive (n=153), bipolar (n=213) and rapid cycling (n=69) mood disorders and 456 controls; for TPH we genotyped 399 inpatients (MD, n=132; BP, n=203; rapid cycling n=64) and 259 controls. Random Regression Model analysis was used to investigate the longitudinal time course of the illness. 5-HTTLPR and TPH polymorphisms were not associated with mood disorders time course. However we observed an excess of 5-HTTLPR*long alleles among rapid cycling subjects compared to both controls (P=0.018) and remitting mood disorders (P=0.006). TPH frequencies did not differ between mood disorders subtypes. Our results suggest that 5-HTTLPR variants may confer a susceptibility toward rapid cycling mood disorders.     

Association of the T102C polymorphism of 5-HT2A receptor gene with aura in migraine

OBJECTIVE: To find out the significance of the 5-HT2A receptor gene polymorphism in migraine. Study design: A PCR study in which 61 migraineurs and 44 healthy controls were included. METHODS: The T102C polymorphism of the 5-HT2A receptor gene was studied. The results of the migraineurs and controls were compared. The relationship between the gene polymorphism and aura was also assessed. RESULTS: The representations of the 5-HT2A genotypes were similar in migraineurs and controls (p>0.05) as well as in the male and female migraineurs (p>0.05). The family history of migraine did not associate with 5-HT2A receptor gene polymorphism (p>0.05). There was a significant relationship between the presence of C/C genotype and migraine with aura (p=0.02) while C/T and T/T genotypes were over represented in the patients with migraine without aura (p<0.01). CONCLUSION: The T102C polymorphism of the 5-HT2A receptor gene is not directly related to the increased risk of migraine. The associations between the genotypes of this gene and aura may suggest that 5-HT2A receptor gene polymorphism may be involved in determining the subtypes of or accompanying symptoms in the migraine disease.     

Serotonin receptor 2A, 2C, 1A genes and response to lithium prophylaxis in mood disorders

The aim of this study was to investigate the influence of serotonin receptors 2A, 2C and 1A gene variants on lithium prophylactic efficacy in mood disorders. One hundred and twenty-four subjects affected by bipolar (n=102) and major depressive (n=22) disorder were followed prospectively for an average of 52 months and were typed for 5-HT2A (T102C: n=111, HTP: n=104), 5-HT2C (n=110) and 5-HT1A (n=61) variants. Both 5-HT2A and 5-HT2C variants were not associated with lithium outcome. Consideration of possible stratification effects like gender, polarity, family history, age at onset and duration of lithium treatment did not influence results. No 5-HT1A gene variant was identified. 5-HT2A and 2C variants are not, therefore, associated with lithium prophylactic efficacy in mood disorders.     

Amygdala responsiveness is modulated by tryptophan hydroxylase-2 gene variation

Summary. The tryptophan hydroxylase-2 gene (TPH2) codes for the enzyme of serotonin (5-HT) synthesis in the brain and variation of TPH2 has been implicated in disorders of emotion regulation. Here, we used functional magnetic resonance imaging (fMRI) to demonstrate that a potentially functional variant of TPH2 modulates amygdala responsiveness to emotional stimuli of both negative and positive valence.     

Serotonin-related gene pathways associated with undifferentiated somatoform disorder

It has been suggested that serotonergic hypofunction and serotonergic pathway genes underlie the somatic symptoms of somatoform disorders. We examined a variety of serotonin-related gene polymorphisms to determine whether undifferentiated somatoform disorder is associated with specific serotonin-related gene pathways. Serotonin-related polymorphic markers were assessed using single nucleotide polymorphism (SNP) genotyping. One hundred and two patients with undifferentiated somatoform disorder and 133 healthy subjects were enrolled. The genotype and allele frequencies of tryptophan hydroxylase (TPH)1 A218C, TPH2 rs1386494, serotonin receptor 2A-T102C (5-HTR 2A-T102C), 5-HTR 2A-G1438A and serotonin transporter (5HTTLPR) gene were compared between the groups. The Hamilton Rating Scale for Depression and the somatization subscale of the Symptom Checklist-90-Revised (SCL-90-R) were used for psychological assessment. Patients with undifferentiated somatoform disorder had higher frequencies of the TPH1 C allele than healthy controls (p = 0.02) but the difference was not significant after Bonferroni correction. The frequency of TPH1 genotype also did not differ significantly between the patients and the healthy controls, nor did TPH2 rs1386494, 5-HTR 2A-T102C, 5-HTR 2A-G1438A or 5HTTLPR allele and genotype frequencies differ significantly between the two groups. These findings suggest that a variety of serotonin-related gene pathways are unlikely to be definite genetic risk factors for undifferentiated somatoform disorder. Therefore, the pathogenesis of the disorder may be related to epigenetic factors, including psychosocial and cultural factors. Nonetheless, future studies need to include a larger sample of subjects and polymorphisms of more serotonin-related gene variants.     

The A218C polymorphism of tryptophan hydroxylase gene and migraine.

OBJECTIVE: To determine the significance of the A218C polymorphism of the tryptophan hydroxylase (TPH) gene in migraine. METHODS: Fifty-nine migraineurs and 62 healthy controls were included in the study, and polymerase chain reaction - restriction fragment length polymorphism assays were used to determine TPH A218C polymorphism. RESULTS: There was no association between TPH gene polymorphism and gender, family history of migraine and epilepsy, or aura. There was no significant difference between the allele frequencies of both groups (p>0.05). A significant difference was found between the genotypes of the migraineurs and controls regarding the AA genotype. Homozygosity for the C allele or heterozygosity for the A or C was not associated with the occurrence of migraine (p>0.05), but homozygosity for the A allele was less frequent in the migraineurs (p=0.02). CONCLUSION: Since it is unlikely that TPH polymorphism alters serotonin biosynthesis, its association with migraine may be attributed to linkage disequilibrium with a functional variant within the TPH gene or a nearby gene.     

Deficiency of brain 5-HT synthesis but serotonergic neuron formation in Tph2 knockout mice

The relative contribution of the two tryptophan hydroxylase (TPH) isoforms, TPH1 and TPH2, to brain serotonergic system function is controversial. To investigate the respective role of TPH2 in neuron serotonin (5-HT) synthesis and the role of 5-HT in brain development, mice with a targeted disruption of Tph2 were generated. The preliminary results indicate that in Tph2 knockout mice raphe neurons are completely devoid of 5-HT, whereas no obvious alteration in morphology and fiber distribution are observed. The findings confirm the exclusive specificity of Tph2 in brain 5-HT synthesis and suggest that Tph2-synthesized 5-HT is not required for serotonergic neuron formation.     

Effect of tryptophan hydroxylase-2 gene variants on suicide risk in major depression.

BACKGROUND: Suicide and depressive disorders are strongly associated, yet not all depressed patients commit suicide. Genetic factors may partly explain this difference. We investigated whether variation at the tryptophan hydroxylase-2 (TPH2) gene and its 5' upstream region may predispose to suicide in major depressive disorder (MDD) and whether this predisposition is mediated by impulsive-aggressive behaviors (IABs). METHODS: We genotyped 14 single nucleotide polymorphisms (SNPs) in 259 depressed subjects, 114 of which committed suicide while depressed. Phenotypic assessments were carried out by means of proxy-based interviews. Single-marker and haplotype association analyses were conducted. Differences in behavioral and personality traits according to genotypic variation were investigated, as well as genetic and clinical predictors of suicide. RESULTS: We found two upstream and two intronic SNPs associated with suicide. No direct effect of these variants was observed on IABs. However, a slight association with reward dependence scores was found. Controlling for suicide risk factors, two SNPs (rs4448731 and rs4641527) significantly predicted suicide, along with cluster B personality disorders and family history of suicide. CONCLUSIONS: The TPH2 gene and its 5' upstream region variants may be involved in the predisposition to suicide in MDD; however, our findings do not support the role of IABs as mediators.     

No association of C-1019G promoter polymorphism of 5-HT1A receptor gene with migraine

It is well known that migraine has a strong genetic component, although the type and number of genes involved remains unclear. There is evidence to suggest that serotonin-related genes may be involved in the pathogenesis of migraine. To investigate whether the 5-HT1A receptor gene contributes to the risk of migraine we performed an association study of C-1019G promoter polymorphism of the gene in 102 migraineurs and 93 controls. Subjects were of Han Chinese origin. No significant differences in allele (P=0.82) or genotype frequencies (P=0.71) were seen in migraineurs compared with the controls. When migraine with aura, without aura, with family history, without family history were analyzed separately, the frequencies did not vary significantly. Our results suggest that C-1019G in 5-HT1A is not a major genetic risk factor for migraine.     

A pharmacological evidence of positive association between mouse intermale aggression and brain serotonin metabolism

The neurotransmitter serotonin (5-HT) is involved in the regulation of mouse intermale aggression. Previously, it was shown that intensity of mouse intermale aggression was positively associated with activity of the key enzyme of 5-HT synthesis - tryptophan hydroxylase 2 (TPH2) in mouse brain. The aim of the present study was to investigate the effect of pharmacological activation or inhibition of 5-HT synthesis in the brain on intermale aggression in two mouse strains differing in the TPH2 activity: C57BL/6J (B6, high TPH2 activity, high aggressiveness) and CC57BR/Mv (BR, low TPH2 activity, low aggressiveness). Administration of 5-HT precursor L-tryptophan (300 mg/kg, i.p.) to BR mice significantly increased the 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels in the midbrain as well as the number of attacks and their duration in the resident-intruder test. And vice versa, administration of TPH2 inhibitor p-chlorophenylalanine (pCPA) (300 mg/kg, i.p., for 3 consecutive days) to B6 mice dramatically reduced the 5-HT and 5-HIAA contents in brain structures and attenuated the frequency and the duration of aggressive attacks. At the same time, L-tryptophan or pCPA did not influence the percentage of aggressive mice and the attack latency reflecting the threshold of aggressive reaction. This result indicated that the intensity of intermale aggression, but not the threshold of aggressive reaction is positively dependent on 5-HT metabolism in mouse brain.     

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.