V. De Luca

Analysis of the novel TPH2 gene in bipolar disorder and suicidality

SIR—Genetic factors have been generally implicated in the etiology of suicide, although the precise mechanism and amount of the genetic contribution are not yet well established. The serotonergic system is thought to be trait dependent and associated with disturbances in the regulation of anxiety, impulsivity, and aggression. Furthermore, serotonergic dysfunction has been suggested in suicide based on several observations. For example, low concentration of the metabolite of serotonin (5-HIAA), in CSF has been associated with suicide attempts and completed suicide, and low levels of 5-HT or 5-HIAA were also observed in suicide victims. 5-HT is synthesized in two steps, with tryptophan hydroxylase (TPH) as the rate-limiting enzyme. Thus far, two TPH genes have been identified. The TPH1 gene is located on chromosome 11p15 and has been the focus of a number of genetic studies of suicidality. A recent meta-analysis concluded that the TPH1 intron 7 A218 polymorphism is associated with suicide-related behavior. Interestingly, a new TPH gene (TPH2) located on chromosome 12q21 has recently been described. In mice brain stem, expression of TPH1 appears to be 150 times lower than TPH2, suggesting that TPH2 may play a much more important role in serotonin synthesis in the brain than TPH1. Therefore, we were interested in investigating the putative role of the TPH2 gene in suicide attempters using a large and well-characterized sample of patients with bipolar disorder. TPH2 has three highly polymorphic single-nucleotide polymorphisms (SNPs): hCV245410 (C/T), hCV8376173 (A/G), rs1487280 (A/G). These SNPs are located in introns 1, 5, and 8, respectively. The study population consisted of 336 bipolar patients from 305 families who were recruited in the Toronto area. The mean age at the time of the interview was 35.36710.37 SD. Subjects ranged in age from 16 to 67 years (35710 SD). The mean age at onset for bipolar disorder was 2077.58 SD. Female subjects comprised 62% of the sample. A total of 86 patients attempted suicide. The SCID-I was administered to all subjects by trained clinical interviewers. Suicidality was assessed on a quantitative scale, with the following order: 11⁄4Thoughts of death, 21⁄4Suicide Ideation, 31⁄4Suicide Plan, 41⁄4Suicide Attempt. Among the bipolar patients, 267 patients had history of suicide ideas or attempt and the mean score for all 336 suicide ideation/behavior scores was 2.171.4. The genoptypes of TPH2 hCV245410, hCV8376173, and rs1487280 polymorphisms were determined by Taqman assay (ABI 7000). Allelic and haplotype transmission tests in suicide attempters were performed using TDT and TRANSMIT. The Family Based Association Test (FBAT) was used for analyses of suicide ideation/behavior quantitative traits. All the analyses were performed under the assumption of an additive model. Main results for single marker TDT in attempter patients are shown in Table 1. For the haplotypes of these three polymorphisms in the attempter population, the TRANSMIT analysis showed a nonsignificant global w (0.56, 5 df). When the suicide behavior was analyzed as a quantitative trait by FBAT, no significant differences were found for hCV245410 (z1⁄4 0.051 P1⁄40.959467), hCV8376173 (z1⁄40.090 P1⁄40.928282), and rs1487280 (z1⁄4 0.143; P1⁄40.886). All the eight possible haplotypes showed no significant results when weighted on the suicide behavior as the quantitative trait (Table 2). In bipolar patients, the TDT did not show significant bias for hCV245410 (109 vs 109 transmissions), hCV8376173 (106 vs 104), and rs1487280 (100 vs 105). The global w using TRANSMIT analyzing only frequent haplotypes was not significant in the overall sample (1.8874, 5 df). To our knowledge, this is the first association study between the TPH2 gene and bipolar disorder and suicide behavior. Our results indicate that it is unlikely that the hCV245410–hCV8376173–rs1487280 haplotypes are involved in the suicide behavior in our bipolar sample. The three variants chosen in this study are polymorphic enough to provide good statistical power for this family study design. Moreover, mutation screening of the TPH2 promoter could be very valuable and these 50 flanking variants might be involved in suicide behavior because of the prior evidence that the immunoreactivity and the expression of TPH in the brains of suicide patients is higher. Despite the fact that bipolar disorder has been shown to have a strong genetic component and the serotonergic system is implicated in the pathogenesis of the disorder, we found that all haplotypes of the TPH2 gene were without bias to bipolar probands in the total sample. Although possible biological differences between suicidal ideation and attempted suicide are pointed out in TPH1 association studies where the 218A/C polymorphism was associated with suicide attempt but not with suicide ideation, the main strength of this study is the family-based strategy that is not sensitive to population stratification, the large sample size, and the suicide quantitative trait Molecular Psychiatry (2004) 9, 896–899 & 2004 Nature Publishing Group All rights reserved 1359-4184/04

Regulation of α7-nicotinic receptor subunit and α7-like gene expression in the prefrontal cortex of patients with bipolar disorder and schizophrenia

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Association of HPA axis genes with suicidal behaviour in schizophrenia

Objective:  The α7‐nicotinic receptor subunit gene (CHRNA7) is located at chromosome 15q13–14, a region previously linked with schizophrenia. Genetic association and mRNA expression studies also implicate CHRNA7 in schizophrenia. The CHRNA7 gene has a partial duplication that constitutes the α7‐like nicotinic receptor gene (CHRFAM7A). We hypothesized that major psychoses could affect the expression of both CHRNA7 and CHRFAM7A.

Age of onset in obsessive–compulsive disorder: admixture analysis with a large sample

Family, adoption and twin studies show that genetics influences suicidal behaviour, but do not indicate specific susceptibility variants. Stress response is thought to be mediated by the corticotrophin-releasing hormone (CRH), which is known to be a regulator of the hypothalamic-pituitary-adrenal pathway (HPA). Alterations in HPA system have been related to impulsivity, aggression and suicidal behaviour, common feature in schizophrenia. CRH is the hypothalamic factor that stimulates the pituitary gland. To search for markers conferring genetic susceptibility to suicide, we typed six HPA axis genes (CRH, CRHR1, CRHR2, CRHBP, MC2R, NC3R1) in a cohort of 231 subjects with schizophrenia in which 81 attempted suicide. The genotype analyses yielded significant association between CRH binding protein (CRHBP) and suicide attempt (P = 0.035). The genotype analysis for quantitative measures of suicidal behaviour showed no association. The interaction analysis showed a significant interaction between CRH receptor type 1 (CRHR1) and CRH binding protein (CRHBP) in influencing suicide attempt and the severity of suicidal behaviour. Current results show that genetic variation in HPA axis genes could be associated with suicidal behaviour in schizophrenia. This is to our knowledge the first study on suicidal behaviour investigating the interaction among the HPA axis genes.

The interaction between TPH2 promoter haplotypes and clinical–demographic risk factors in suicide victims with major psychoses

BACKGROUND Research into age of onset in obsessive-compulsive disorder (OCD) has indicated significant differences between patients with early and late onset of the disorder. However, multiple criteria have been used arbitrarily for differentiating between early- and late-onset OCD, rendering inconsistent results that are difficult to interpret. METHOD In the current study, admixture analysis was conducted in a sample of 377 OC patients to determine the number of underlying populations of age of onset and associated demographic and clinical characteristics. Various measures of anxiety, depression, co-morbidity, autism, OCD, tics and attention deficit hyperactivity disorder (ADHD) symptoms were administered. RESULTS A bimodal age of onset was established and the best-fitting cut-off score between early and late age of onset was 20 years (early age of onset ≤19 years). Patients with early age of onset were more likely to be single. Early age of onset patients demonstrated higher levels of OCD severity and increased symptoms on all OCD dimensions along with increased ADHD symptoms and higher rates of bipolar disorder. CONCLUSIONS It is suggested that 20 years is the recommended cut-off age for the determination of early versus late age of onset in OCD. Early age of onset is associated with a generally graver OCD clinical picture and increased ADHD symptoms and bipolar disorder rates, which may be related to greater functional implications of the disorder. We propose that age of onset could be an important marker for the subtyping of OCD.

Untranslated region haplotype in dysbindin gene: analysis in schizophrenia.

Tryptophan hydroxylase isoform 2 (TPH2) is a rate‐limiting enzyme in the biosynthesis of serotonin (5‐HT) and is predominantly localized in the brain. Previous studies have suggested that there is an association between serotonergic dysfunction in the brain and suicidality. This study was designed to examine whether the −473T > A and −8396G > C polymorphisms of the TPH2 gene may be associated with completed suicide in subjects with major psychoses from the Stanley Foundation Brain Bank sample. TPH2 genotypes were determined in 69 subjects with a diagnosis of schizophrenia or bipolar disorder, among which 22 died by suicide. Genomic DNA was amplified by polymerase chain reaction and typed by automated methods. Both markers were found to be in Hardy–Weinberg equilibrium and in strong linkage disequilibrium. No association with history of suicide was found for either polymorphism. Haplotype analysis with ehap showed no association between completed suicide and haplotype distribution (χ2 = 1.877; 3 df; P = 0.598). Nor was there any association between suicide and these genetic markers even when clinical–demographic factors were considered as covariates in the haplotype analysis. These findings suggest that these 5′ marker haplotypes in the TPH2 gene do not influence suicidal behaviour.

p75NTR gene and suicide attempts in young adults with a history of childhood-onset mood disorder†‡

Summary.Genome-scans performed in schizophrenia families have provided evidence for region 6p24-21 where variability may confer susceptibility to schizophrenia. Recent studies have implicated that gene DTNBP1 (dysbindin) in this region is strongly associated with schizophrenia. In a family based association study we investigated three markers located in the untranslated region of the DTNBP1 gene: rs909706, rs1047631 and rs742106. The sample size of our study is 117 families. No biased transmission towards the disorder was detected by haplotype analysis using TRANSMIT.

Cortical BDNF and NTRK2 Transcript Expression in Completed Suicide

Recently, evidence has accumulated for the role of neurotrophic processes in mood disorders. Neurotrophins operate on receptors, one of which is the p75 neurotrophin receptor (p75NTR). We examined three p75NTR markers at the p75NTR gene, including a missense polymorphism that changes serine to leucine (S205L), for association with suicide attempt (SA) in 203 childhood‐onset mood disorder (COMD) cases. There was no difference between COMD suicide attempters and COMD non‐attempters with logistic regression models for any of the three markers. We also compared the three polymorphisms between 192 COMD cases and 192 matched healthy controls and found no significant differences between COMD and healthy controls. Our results do not support an association of the p75NTR S205L polymorphism with risk for COMD or SA in COMD.

PW01-54 - Correlation of a set of gene variants, life events and personality features on adult ADHD severity

Expression of neurotrophin system transcripts will be diminished in suicide compared to other causes of death in anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC), similar to a prior study. We used publicly available microarray data on 32 postmortem subjects from two cohorts. Covariates selected for inclusion in a logistic regression model included cohort and pH. Neither brain-derived neurotrophic factor (BDNF; Wald chisq = 0.00, df=1, p=0.95) nor tyrosine kinase B (NTRK2; Wald chisq = 0.41, df=1, p=0.52) transcript expression were altered in the ACC of subjects with completed suicide compared to other causes of death. In the DLPFC of suicide subjects, no differences in BDNF (Wald chisq = 0.30, df=1, p=0.58) or NTRK2 (Wald chisq = 2.13, df=1, p=0.14) expression were noted. Specific laboratory methods and sampling factors may explain the negative findings. The present data do not exclude the possibility of altered BDNF and NTRK2 expression in completed suicide.

P.1.24 Serotonin transporter gene and adverse life events in adult ADHD

Objective Increasing evidence suggests that symptoms of Attention Deficit Hyperactivity disorder (ADHD) could persist into adult life in a substantial proportion of cases. The aim of the present study is to investigate the impact of 1) adverse events, 2) personality traits and 3) genetic variants chosen on the basis of previous findings and 4) their possible interactions on adult ADHD severity in a sample of 110 Caucasian patients. Methods One hundred and ten individuals diagnosed with adult ADHD were evaluated for occurrence of adverse events in childhood and adulthood, and personality traits by the Temperament and Character Inventory (TCI). Common polymorphisms within a set of nine important candidate genes ( SLC6A3, DBH, DRD4, DRD5, HTR2A, CHRNA7, BDNF, PRKG1 and TAAR9 ) were genotyped for each subject. Life events, personality traits and genetic variations were analyzed in relationship to severity of current symptoms, evaluated by the Brown Attention Deficit Disorder Scale (BADDS). Results Genetic variations were not significantly associated with severity of ADHD symptoms and life stressors displayed only a minor effect as compared to personality traits. Indeed, symptoms’ severity was significantly correlated with the temperamental trait of Harm avoidance and the character trait of Self directedness. Conclusions The results of the present work are in line with previous evidence of a significant correlation between some personality traits and adult ADHD. However, several limitations such as the small sample size and the exclusion of patients with other severe comorbid psychiatric disorders could have influenced the significance of present findings.