Two naturally occurring amino acid substitutions of the 5-HT2A receptor: similar prevalence in patients with seasonal affective disorder and controls

Investigating DRD2 and HTR2A polymorphisms in treatment-resistant schizophrenia: a comparative analysis with other treatment-resistant mental disorders and the healthy state

This study investigates treatment-resistant schizophrenia (TRS) by analysing genetic markers in dopamine and serotonin receptors. Conducted on a cohort of 221 patients with treatment-resistant mental disorders, the research focused on DRD2 and HTR2A gene variants-specifically, rs1801028, rs6314, rs7997012, and rs6311. The findings suggest specific associations between certain genetic variants and TRS. Notably, the HTR2A rs6314 A|G genotype and rs7997012 G|G genotype were significantly more prevalent in TRS patients compared to healthy controls (HCs). Haplotype analyses revealed associations between specific haplotypes-such as A|G (rs6314-rs7997012)-and TRS, indicating their potential predictive value for TRS versus HCs. The study underscores the involvement of the serotonergic system in TRS. These findings offer valuable insights into the genetic factors contributing to TRS, paving the way for future research and the development of personalised prevention and treatment strategies in psychiatry.

His452Tyr 5-HT2A polymorphism and intravaginal ejaculation latency time in Dutch men with lifelong premature ejaculation

Lifelong premature ejaculation (LPE) may have heritable components. Selective serotonin reuptake inhibitors have been proven effective in prolonging intravaginal ejaculation latency time (IELT). Given that serotonergic pathways are involved in the ejaculation mechanism, we aimed to investigate whether His452Tyr, also known as the C1354T (RS6314) polymorphism of the 5-HT_2A receptor, contributes to LPE pathogenesis and IELT differences among patients with LPE. Dutch Caucasian men with LPE (n = 65) attending the Outpatient Department of Neurosexology, HagaZiekenhuis for drug treatment for LPE in 2009 were selected and included in this case-control study. IELT during coitus was measured using a stopwatch, and all men were genotyped for the His452Tyr polymorphism. Analysis of variance (ANOVA) was performed to determine the association between the genotypes and IELTs. Mean IELTs with standard deviations were 29.7 (±20.9), 31.5 (±14.7), and 26.0 s, and the frequencies were 83.1%, 15.4%, and 1.5% for the CC, CT, and TT groups, respectively, with an average IELT of 29.9 s. No difference in mean IELT was observed between these groups. In the affected group, the frequencies of alleles C and T were 90.8% and 9.2%, respectively; whereas those among randomly selected European Caucasian male controls (n = 503) from the CEPH database were of 92.0% and 8.0%, respectively. No significant difference was observed between the groups. Therefore, no correlation was found between the His452Tyr polymorphism and IELT distribution in patients with LPE.

The impact of COMT, BDNF and 5-HTT brain-genes on the development of anorexia nervosa: a systematic review

PURPOSE

The genetic aspect of anorexia nervosa (AN) involving specific genes of the central-nervous-system has not yet been clearly understood. The aim of this systematic review is to assess the impact of three candidate genes of the brain: catechol-O-methyltransferase, brain-derived neurotrophic factor (BDNF) and serotonin transporter protein, on the susceptibility to AN and identify whether a clear connection persists between each of the gene-polymorphisms and AN.

METHODS

A total of 21 articles were selected for this review conforming to the PRISMA guidelines. Detailed keyword combinations were implemented within specific databases such as MEDLINE, SCIENCEDIRECT and PUBMED.

RESULTS

The catechol-O-methyltransferase gene-polymorphism did not show any change in phenotypic variation between AN and control subjects; but the familial association was rather strong with an over-transmission of the H allele. The latter also correlated with several dimensions of the Temperament and Character Inventory (TCI) scale. A notable relation was indicated between BDNF gene-polymorphism and anorexia-restrictive in terms of phenotypic distribution; the Met66-allele also depicted high association with anorexic behavioral traits. The 5-HTTLPR gene-polymorphism was found to be significantly associated with AN susceptibility with an over-transmission of the S-allele from parents to offspring.

CONCLUSION

The systematic review distinctively emphasized the genetic contribution of the brain-genes on the development of AN. Despite significant study findings, no clear and standardized genetic route was determined to be the cause of AN development. Future research is needed on these specific genes to closely monitor the genetic polymorphisms and their mechanism on AN susceptibility.

LEVEL OF EVIDENCE

I, systematic review.

Additive genetic risk from five serotonin system polymorphisms interacts with interpersonal stress to predict depression

Behavioral genetic research supports polygenic models of depression in which many genetic variations each contribute a small amount of risk, and prevailing diathesis-stress models suggest gene-environment interactions (G×E). Multilocus profile scores of additive risk offer an approach that is consistent with polygenic models of depression risk. In a first demonstration of this approach in a G×E predicting depression, we created an additive multilocus profile score from 5 serotonin system polymorphisms (1 each in the genes HTR1A, HTR2A, HTR2C, and 2 in TPH2). Analyses focused on 2 forms of interpersonal stress as environmental risk factors. Using 5 years of longitudinal diagnostic and life stress interviews from 387 emerging young adults in the Youth Emotion Project, survival analyses show that this multilocus profile score interacts with major interpersonal stressful life events to predict major depressive episode onsets (hazard ratio [HR] = 1.815, p = .007). Simultaneously, there was a significant protective effect of the profile score without a recent event (HR = 0.83, p = .030). The G×E effect with interpersonal chronic stress was not significant (HR = 1.15, p = .165). Finally, effect sizes for genetic factors examined ignoring stress suggested such an approach could lead to overlooking or misinterpreting genetic effects. Both the G×E effect and the protective simple main effect were replicated in a sample of early adolescent girls (N = 105). We discuss potential benefits of the multilocus genetic profile score approach and caveats for future research.

Variation in Dopamine D2 and Serotonin 5-HT2A Receptor Genes is Associated with Working Memory Processing and Response to Treatment with Antipsychotics

Dopamine D2 and serotonin 5-HT2A receptors contribute to modulate prefrontal cortical physiology and response to treatment with antipsychotics in schizophrenia. Similarly, functional variation in the genes encoding these receptors is also associated with these phenotypes. In particular, the DRD2 rs1076560 T allele predicts a lower ratio of expression of D2 short/long isoforms, suboptimal working memory processing, and better response to antipsychotic treatment compared with the G allele. Furthermore, the HTR2A T allele is associated with lower 5-HT2A expression, impaired working memory processing, and poorer response to antipsychotics compared with the C allele. Here, we investigated in healthy subjects whether these functional polymorphisms have a combined effect on prefrontal cortical physiology and related cognitive behavior linked to schizophrenia as well as on response to treatment with second-generation antipsychotics in patients with schizophrenia. In a total sample of 620 healthy subjects, we found that subjects with the rs1076560 T and rs6314 T alleles have greater fMRI prefrontal activity during working memory. Similar results were obtained within the attentional domain. Also, the concomitant presence of the rs1076560 T/rs6314 T alleles also predicted lower behavioral accuracy during working memory. Moreover, we found that rs1076560 T carrier/rs6314 CC individuals had better responses to antipsychotic treatment in two independent samples of patients with schizophrenia (n=63 and n=54, respectively), consistent with the previously reported separate effects of these genotypes. These results indicate that DRD2 and HTR2A genetic variants together modulate physiological prefrontal efficiency during working memory and also modulate the response to antipsychotics. Therefore, these results suggest that further exploration is needed to better understand the clinical consequences of these genotype-phenotype relationships.

Meta-analysis of genetic association studies on bipolar disorder

Numerous candidate gene association studies of bipolar disorder (BP) have been carried out, but the results have been inconsistent. Individual studies are typically underpowered to detect associations with genes of small effect sizes. We conducted a meta-analysis of published candidate gene studies to evaluate the cumulative evidence. We systematically searched for all published candidate gene association studies of BP. We then carried out a random-effects meta-analysis on all polymorphisms that were reported on by three or more case-control studies. The results from meta-analyses of these genes were compared with the findings from a recent mega-analysis of eleven genome-wide association studies (GWAS) in BP performed by the Psychiatric GWAS Consortium (PGC). A total of 487 articles were included in our review. Among these, 33 polymorphisms in 18 genes were reported on by three or more case-control studies and included in the random-effects meta-analysis. Polymorphisms in BDNF, DRD4, DAOA, and TPH1, were found to be nominally significant with a P-value < 0.05. However, none of the findings were significant after correction for multiple testing. Moreover, none of these polymorphisms were nominally significant in the PGC-BP GWAS. A number of plausible candidate genes have been previously associated with BP. However, the lack of robust findings in our review of these candidate genes highlights the need for more atheoretical approaches to study the genetics of BP afforded by GWAS. The results of this meta-analysis and from other on-going genomic experiments in BP are available online at Metamoodics (http://metamoodics.igm.jhmi.edu).

Genetics of human episodic memory: dealing with complexity

Episodic memory is a polygenic behavioral trait with substantial heritability estimates. Despite its complexity, recent empirical evidence supports the notion that behavioral genetic studies of episodic memory might successfully identify trait-associated molecules and pathways. The development of high-throughput genotyping methods, of elaborated statistical analyses and of phenotypic assessment methods at the neural systems level will facilitate the reliable identification of novel memory-related genes. Importantly, a necessary crosstalk between behavioral genetic studies and investigation of causality by molecular genetic studies will ultimately pave the way towards the identification of biologically important, and hopefully druggable, genes and molecular pathways related to human episodic memory.

Effects of the serotonin 1A, 2A, 2C, 3A, and 3B and serotonin transporter gene polymorphisms on the occurrence of paroxetine discontinuation syndrome

Paroxetine discontinuation symptoms can at times be severe enough to reduce the quality of life. However, it is currently not possible to predict the occurrence of discontinuation syndrome before the initiation or discontinuation of paroxetine treatment. In this study, we investigated the effects of genetic polymorphisms in the serotonin 1A, 2A, 2C, 3A, and 3B receptor, the serotonin transporter, and the cytochrome P450 2D6 (CYP2D6) genes on the occurrence of paroxetine discontinuation syndrome. A consecutive series of 56 Japanese patients who had a diagnosis of major depressive or anxiety disorder according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, were treated with paroxetine. Paroxetine discontinuation syndrome was found in 35.7% of the patients by direct interview. Patients who stopped taking paroxetine abruptly experienced paroxetine discontinuation syndrome significantly more often than patients who had a tapering off of the dosage of medication. Patients who had the -1019C allele experienced paroxetine discontinuation syndrome more frequently than patients who had the -1019G homozygote (nominal P = 0.0423) of the serotonin 1A receptor gene. However, this result did not remain significant after the Bonferroni correction for multiple comparisons. The findings suggest that the abrupt stoppage of medication is a major risk factor for the occurrence of paroxetine discontinuation syndrome and that C(-1019)G polymorphism of the serotonin 1A receptor gene may be related to the occurrence of the syndrome.

Genetic variation in the serotonin 2A receptor and suicidal ideation in a sample of 270 Irish high-density schizophrenia families

Genetic variation in the serotonin 2A receptor (HTR2A) has been associated with both schizophrenia and suicidal behavior. Our sample comprised 270 Irish high-density schizophrenia families (n = 1,408 subjects, including 755 with psychotic illness). Diagnoses were generated using a modified SCID. All patients who had at least one episode of psychosis were rated on the Operation Criteria Checklist for Psychotic Illness (OPCRIT). Lifetime history of suicidal ideation was determined from medical records and psychiatric interviews and was scored in the OPCRIT. Twelve SNPs were selected for study. Ten of these were tagSNPs derived from HapMap data, along with His452Tyr and T102C. We tested for association with psychotic illness as a whole, as well as stratified by the presence of suicidal ideation, using FBAT and PDTPHASE. Single-marker as well as haplotype-based tests using a "sliding window" approach were performed. We observed several 2, 3, and 4 marker haplotypes near the 3' end of the gene that were over-transmitted to psychotic subjects (0.02 </= P </= 0.04). His452Tyr was included in these haplotypes but was not itself significant. We also observed modest over-transmission of a 2-marker haplotype that included T102C (0.04 </= P </= 0.08), which was also not itself significant in single-marker analyses. There was no significant association in the subgroup of the sample with suicidal ideation. Because of multiple testing, these results do not provide support for HTR2A as a susceptibility gene for psychotic illness, or for suicidal ideation within psychotic illness.

A polymorphism in the human serotonin 5-HT2A receptor gene may protect against systemic sclerosis by reducing platelet aggregation

INTRODUCTION

Platelet aggregation may contribute to the pathogenesis of systemic sclerosis: following activation, platelets release significant amounts of serotonin - which promotes vasoconstriction and fibrosis, and further enhances aggregation. The C+1354T polymorphism in the exonic region of the serotonin 2A receptor gene determining the His452Tyr substitution was associated with blunted intracellular responses after serotonin stimulation, and may have a role in susceptibility to scleroderma.

METHODS

One hundred and fifteen consecutive systemic sclerosis patients and 140 well-matched healthy control individuals were genotyped by sequence-specific primer-PCR for the His452Tyr substitution of the serotonin 2A receptor gene, and associations were sought with scleroderma and its main clinical features. The functional relevance of the His452Tyr substitution was also assessed by evaluating the aggregation of platelet-rich plasma from His452/His452 and His452/Tyr452 healthy individuals after stimulation with adenosine diphosphate +/- serotonin.

RESULTS

The T allele of the C+1354T polymorphism was underrepresented in scleroderma patients compared with control individuals (5.2% versus 12.4%, P < 0.001, chi-square test and 1,000-fold permutation test) and its carriage reduced the risk for systemic sclerosis (odds ratio = 0.39, 95% confidence interval = 0.19 to 0.85, P < 0.01). Platelets from His452/Tyr452 healthy subjects more weakly responded to serotonin stimulation compared with platelets from His452/His452 individuals (3.2 +/- 2.6-fold versus 9.6 +/- 8.6-fold increase in aggregation, P = 0.017 by Kolmogorov-Smirnov test and P = 0.003 after correction for baseline adenosine diphosphate-induced aggregation values).

CONCLUSION

The His452Tyr substitution may influence susceptibility to systemic sclerosis by altering platelet aggregation in response to serotonin.

Association study of two polymorphisms of the serotonin-2A receptor gene and suicide attempts

Serotonin (5-HT) receptors may have a role in suicidal behavior. Previous studies have shown an association between the T102C polymorphism of the 5-HT2a receptor gene and suicidal behavior. However, negative findings have also been reported. We examined the association between the T102C and C1354T (His452Tyr) polymorphisms of the 5-HT2a receptor gene and suicide attempts. Four hundred forty-one suicide attempters, 339 psychiatric patients, and 410 healthy controls were compared for genotypes of the T102C and C1354T (His452Tyr) polymorphisms. There were significant differences in the distribution of the three genotypes (TT, TC, and CC) of the T102C polymorphism in the three groups (controls, psychiatric patients, and suicide attempters). There was an excess of C/C genotypes in the suicide attempter group compared with the control group, but there were no significant differences between suicide attempters and psychiatric controls. We found no association between the C1354T polymorphism and suicide attempts. The C allele of the T102C polymorphism of the 5-HT2A receptor gene may be associated with biological susceptibility for suicidal behavior or psychiatric conditions.

[Affective disorders and biological rhythms]

Disruptions of circadian rhythms are described in affective disorders, including unipolar and bipolar disorder, but also seasonal affective disorder. Sleep-wake and hormone circadian rhythms are among the most quoted examples. Depression could be conceptualized as a desynchronization between the endogenous circadian pacemaker and the exogenous stimuli, such as sunlight and social rhythms. Accordingly, Clock genes have been studied and the literature suggests that variants in these genes confer a higher risk of relapse, more sleep disturbances associated with depression, as well as incomplete treatment response. Most of therapeutic interventions in depression have an impact on biological rhythms. Some of them exclusively act via a biological pathway, such as sleep deprivation or light therapy. Some psychosocial interventions are specifically focusing on social rhythms, particularly in bipolar disorder, in which the promotion of stabilization is emphasized. Finally, all antidepressant medications could improve biological rhythms, but some new agents are now totally focusing this novel approach for the treatment of depression.

Genetic polymorphisms in the 5-hydroxytryptamine type 3B receptor gene and paroxetine-induced nausea

Selective serotonin reuptake inhibitor (SSRI)-induced nausea can be severe enough to lead to early treatment discontinuation. However, it is currently not possible to predict the occurrence of nausea before the initiation of SSRI treatment. In this study, we investigated the effect of genetic polymorphisms in the 5-hydroxytryptamine type 2A, 3A, and 3B (5-HT3B) receptors, 5-HT transporter, and CYP2D6 genes on the incidence of paroxetine-induced nausea. A consecutive series of 72 Japanese patients with depressive or anxiety disorders were treated with paroxetine. Paroxetine-induced nausea was assessed by a pharmacist and was observed in 29.2% of the patients. A significant (nominal p=0.00286) association was found between the incidence of nausea and the -100_-102AAG insertion/deletion polymorphism of the 5-HT3B receptor gene. No significant associations were observed between the other genetic polymorphisms and the incidence of nausea. The -100_-102AAG deletion variant of the 5-HT3B receptor gene may affect paroxetine-induced nausea.

Direct analysis of candidate genes in impulsive behaviours

Antisocial behaviour is both heterogeneous and the product of interacting genetic and environmental factors acting at different levels of causation. Heritability studies show that individual differences in predisposition to antisocial behaviour are transmitted vertically in families by genetic mechanisms. Owing to aetiological heterogeneity and complexity, study of a variety of other behavioural phenotypes may shed more light on the antecedents of antisocial behaviour than direct studies on antisocial behaviour. Identification of genetic vulnerability factors would clarify mechanisms of vulnerability and the role of the environment. Direct gene analysis and genetic linkage analysis have identified structural variants in genes involved in neurotransmitter function, and some progress has been made towards relating these genetic variants to antisocial personality and other behaviours. Thyroid hormone receptor variants can cause attention deficit/hyperactivity disorder, and a monoamine oxidase A variant leads to aggressive behaviour in one family. Direct gene analyses have revealed non-conservative amino acid substitutions and structural variants (generally rare) at DRD2, DRD3 and DRD4 dopamine receptors and 5-HT1A, 5-HT2A, 5-HT2C and 5-HT7 serotonin receptors. The stage is set to identify the phenotypic significance of these as well as genetic variants at other loci which may be relevant as candidate genes for antisocial behaviour and related behavioural differences.

No significant association between response to methylphenidate and genes of the dopaminergic and serotonergic systems in a sample of Brazilian children with attention-deficit/hyperactivity disorder

Few studies on pharmacogenetics of Attention-Deficit/Hyperactivity Disorder (ADHD) have been conducted. Most of them evaluated dopaminergic genes resulting in positive and negative findings. We assessed effects of polymorphisms in candidate dopaminergic (DRD4, DAT1) and serotonergic genes (HTR1B, HTR2A, and 5-HTT) on the response to treatment in 111 patients for whom methylphenidate (MPH) was prescribed. Outcome measures (Swanson, Nolan, and Pelham scale-version IV, Children Global Assessment Scale, Barkley's Stimulants Side Effects Rating Scale) were assessed at baseline and 1 month after the intervention. No significant association was detected between polymorphisms assessed and both response and side effects to MPH. Prospective multi-site controlled studies with larger sample sizes are needed in order to disentangle the role of candidate genes in response to ADHD treatment.

Supportive evidence for the association between the T102C 5-HTR2A gene polymorphism and schizophrenia: a large-scale case-control and family-based study

Serotonin type 2A receptors (5-HTR2A) have long been implicated in schizophrenia pathology. A decreased number of these receptors were found in postmortem brain studies of schizophrenic patients as well as in experiments using neuroimaging techniques. Molecular genetic studies revealed that the T102C polymorphism of the 5-HTR2A gene is associated with schizophrenia, with the CC genotype frequency being higher in patients compared to healthy controls. However the association was not confirmed in all studies. We carried out a replication study, which aimed at searching for association between this polymorphism and schizophrenia in a large samples of patients (n=919), their psychiatrically well first-degree relatives (n=330) and screened controls (n=500). The C allele and the CT+CC genotype frequencies were significantly higher in patients than in controls (chi2=5.1; df=1; p=0.02; OR 1.2, 95% CI 1.0-1.4) and chi2=5.4; df=1; p=0.02; OR 1.4, 95% CI 1.1-1.8 respectively). In a family-based study, the transmission disequilibrium test (TDT) and the family-based association test (FBAT) did not show a preferential transmission of any allele. In conclusion, our replication study provides further evidence for association between the 5-HTR2A receptor T102C polymorphism and schizophrenia.

Serotonin genes and attention deficit/hyperactivity disorder in a Brazilian sample: preferential transmission of the HTR2A 452His allele to affected boys

Attention-deficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood. The role of genetic factors in its etiology is strongly supported by family, adoption, and twin studies. Low serotonin activity has been associated in both animal and human studies with measures of impulsivity, aggression, and disinhibited behaviors, which make genes from the serotonin system reasonable candidates for ADHD susceptibility. In the present study, we investigated a polymorphism in the promoter region of the serotonin transporter (SLC6A4) and two polymorphisms (-1438 A > G and His452Tyr) in the serotonin 5-HTR2A receptor gene using family based association analyses in a sample of 243 Brazilian ADHD children and adolescents and their parents. No linkage disequilibrium between the two HTR2A polymorphisms was detected in this sample (P = 0.76). Considering several evidences from animal models for sexual dimorphism in serotonin genes expression, analyses were performed separately for the whole sample and for male probands. No evidences for biased transmissions of both HTR2A -1438 A > G and SLC6A4 polymorphisms to ADHD youths were observed. Preferential transmission of the HTR2A His452 allele was observed only in families with affected boys (P = 0.04). Our results suggest that findings from ADHD association studies for serotonin genes might be understood in the context of a gender effect, which may help to explain conflicting results in these association studies.

Serotonin 2A receptor gene is associated with personality traits, but not to disorder, in patients with borderline personality disorder

Borderline personality disorder (BPD) is a chronic, disabling, and high-risk mental disorder characterized by a pervasive pattern of instability in regulation of emotion, interpersonal relationships, self-image, and impulse control beginning in early adulthood. BPD affects about 1%-2% of the general population and has a high mortality rate as a result of suicide and impulsive behaviour. The serotonin 2A receptor gene (HTR2A) is considered a candidate gene for BPD because multiple lines of evidence suggest that it plays an important role in suicide, impulsivity and emotional liability. To test for an association between HTR2A and BPD, we genotyped four polymorphisms, rs6313 (T102C), rs4941573, rs2296972 and rs6314 (His452Tyr), in 111 Caucasian patients with BPD and 287 Caucasian healthy controls. The program UNPHASED was used to compare allele and haplotype frequencies between cases and controls. We did not find a significant association between HTR2A and BPD based on allele, genotype or haplotype analyses. However, there were significant associations between HTR2A and personality traits in the BPD patients. The C allele of rs6313 and the A allele of rs4941573 associated with a higher Extraversion score. Our results suggest that the serotonin 2A receptor gene may not play a major role in the aetiology of borderline personality disorder, but may have a role in personality traits.

5-Hydroxytryptamine receptors in the human cardiovascular system

The human cardiovascular system is exposed to plasma 5-hydroxytryptamine (5-HT, serotonin), usually released from platelets. 5-HT can produce harmful acute and chronic effects. The acute cardiac effects of 5-HT consist of tachycardia (preceded on occasion by a brief reflex bradycardia), increased atrial contractility and production of atrial arrhythmias. Acute inotropic, lusitropic and arrhythmic effects of 5-HT on human ventricle become conspicuous after inhibition of phosphodiesterase (PDE) activity. Human cardiostimulation is mediated through 5-HT4 receptors. Atrial and ventricular PDE3 activity exerts a protective role against potentially harmful cardiostimulation. Chronic exposure to high levels of 5-HT (from metastatic carcinoid tumours), the anorectic drug fenfluramine and its metabolites, as well as the ecstasy drug 3,4-methylenedioxymethamphetamine (MDMA) and its metabolite 3,4-methylenedioxyamphetamine (MDA) are associated with proliferative disease and thickening of cardiac valves, mediated through 5-HT2B receptors. 5-HT2B receptors have an obligatory physiological role in murine cardiac embryology but whether this happens in humans requires research. Congenital heart block (CHB) is, on occasion, associated with autoantibodies against 5-HT4 receptors. Acute vascular constriction by 5-HT is usually shared by 5-HT1B and 5-HT2A receptors, except in intracranial arteries which constrict only through 5-HT1B receptors. Both 5-HT1B and 5-HT2A receptors can mediate coronary artery spasm but only 5-HT1B receptors appear involved in coronary spasm of patients treated with triptans or with Prinzmetal angina. 5-HT2A receptors constrict the portal venous system including oesophageal collaterals in cirrhosis. Chronic exposure to 5-HT can contribute to pulmonary hypertension through activation of constrictor 5-HT1B receptors and proliferative 5-HT2B receptors, and possibly through direct intracellular effects.

Risperidone-related weight gain: genetic and nongenetic predictors

OBJECTIVE

A serious side effect of atypical antipsychotics is increased body weight, which leads to further morbidity and nonadherence to medication. It has been suggested that both genetic and nongenetic variables may influence antipsychotics-related weight gain. This study aimed to simultaneously explore the effects of multiple candidate genes and environment factors on body weight of schizophrenia patients who received risperidone, a commonly used atypical antipsychotic agent.

METHODS

One hundred twenty-three ethnically Han Chinese inpatients with acutely exacerbated schizophrenia were given risperidone monotherapy for up to 42 days. Body weight and clinical manifestations were assessed biweekly. Drug efficacy was measured by the Positive and Negative Syndrome Scale (PANSS), and safety was evaluated by the Extrapyramidal Symptom Rating Scale (ESRS) and the UKU Side Effect Rating Scale. We collected body weight as the response value. Potential prognostic factors were baseline body weight, age, sex, diagnosis subtypes, risperidone dosage, PANSS total scores, treatment duration (weeks 0-6), and 15 genetic variants [across 10 candidate genes: 5-HT1A, 5-HT2A, 5-HT2C, 5-HT6, D1, D2, D3, and alpha1-adrenergic receptors, brain-derived neurotrophic factor (BDNF), and cytochrome P450 2D6 (CYP2D6)]. Because there were repeated assessments, multiple linear regression with the generalized estimating equation (GEE) method was used to adjust the within-subject dependence.

RESULTS

Of 15 genetic polymorphisms examined, 5-HT2A 102-T/C, 5-HT2C -759-C/T, 5-HT6 267-C/T, BDNF 66-Val/Met, and CYP2D6 188-C/T significantly influenced body weight, and so did baseline body weight, age, gender, schizophrenia subtype, and treatment duration and efficacy.

CONCLUSIONS

These results suggest that numerous genetic and nongenetic factors affect antipsychotics-related weight gain.

Influence of serotonin receptor 2A His452Tyr polymorphism on brain temporal structures: a volumetric MR study

Serotonin (5-HT) receptors 2A are expressed in brain regions involved in memory and learning processes. Recently, a functional single nucleotide polymorphism in the 5-HT2A receptor gene leading to an amino-acid substitution at residue 452 (His452Tyr) has been involved in memory performance, persons with the rare 452Tyr allele showing poorer memory performance compared to His452His subjects. To investigate a putative structural effect of this polymorphism on temporal areas typically involved in memory processes, we performed voxel-based morphometry (VBM) and region-of-interest (ROI) volumetric analysis on high-resolution magnetic resonance images in 15 carriers and 61 noncarriers of the 452Tyr allele. ROI volumetric analysis showed a significant reduction of the fractional volume of the temporal white matter in 452Tyr carriers (0.67+/-0.07 vs 0.73+/-0.08; P=0.007). VBM confirmed this finding and in addition showed reduced grey matter in the left hippocampus, left inferior temporal gyrus, and bilaterally in the middle and superior temporal gyrus. A possible effect on synaptic plasticity or neurodevelopment might explain the influence of the His452Tyr polymorphism on temporal brain structures, and this might be the basis for poorer memory performance in 452Tyr carriers. These findings should be considered preliminary and future replication is needed.

Update on the biology of seasonal affective disorder

The etiology and pathophysiology of seasonal affective disorder (SAD) has been linked to the seasons and to light since its first conceptualization. Aspects of SAD that make it particularly amenable to biological investigation include the predictable recurrent episodes, the rapid response to a nonpharmacologic treatment, the specific neurovegetative features, and the availability of rich animal models of seasonality. This paper reviews new findings for the major biological hypotheses for SAD, focusing on circadian rhythms, neurotransmitters, and molecular genetics. Integrative issues and future directions for the study of SAD, including the heuristic value of a dual-vulnerability hypothesis that conceptualizes seasonality as a dimensional construct and the importance of studying endophenotypes, will be discussed.

Inter-relationships of intermediate phenotypes for serotonin function, impulsivity, and a 5-HT2A candidate allele: His452Tyr

Central serotonin (5-hydroxytryptamine, 5-HT) function has a role in a range of genetically influenced psychiatric diagnoses and behaviors. Several human 5-HT receptor polymorphisms are 'candidate alleles', altering in vitro function, and potentially affecting behavior and drug response. The 5-HT(2A) His452Tyr polymorphism alters signal transduction, and has been associated with diminished efficacy of clozapine in schizophrenia. Another 5-HT(2A) receptor polymorphism consists of the silent thymidine-cytosine substitution (102T>C), which has been controversially associated with schizophrenia. We investigated the role of His452Tyr and the 102T>C in behavior and in vivo intermediate biochemical phenotypes. Intracellular 5-HT-induced Ca(2+) release by platelets and fenfluramine-induced prolactin release by pituitary were evaluated in 27 psychiatrically interviewed subjects (including both impulsive patients and controls) stratified by His452Tyr genotype and also genotyped for a second 5-HT(2A) polymorphism, 102T>C. Subjects with increased measures of impulsivity showed decreased postreceptor 5-HT function, as indicated by reduced 5-HT-induced Ca(2+) release, but no alteration in net 5-HT function, as measured by fenfluramine response. No significant effects of either polymorphism were associated with altered 5-HT-induced calcium response or fenfluramine-stimulated prolactin release. One available Tyr452/Tyr452 homozygote had diminished Ca(2+) release and one of the highest levels of fenfluramine response. Although not statistically significant, the effect of the T102C, but not the His452Tyr, genotype on prolactin level change over time was associated with a medium to large strength of association (treatment magnitude of T(2)=0.10), suggesting that further study is warranted.

Effect of DRD2, 5-HT2A, and COMT genes on antipsychotic response to risperidone

Risperidone is a widely used atypical antipsychotic with certain advantages over typical antipsychotics. Although variations in the efficacy of treatment with risperidone have been observed, no specific predictable marker has been identified as of yet. In all, 73 Japanese patients with schizophrenia were given risperidone for 8 weeks, and clinical symptoms were evaluated using the Positive and Negative Syndrome Scale (PANSS). Six candidate polymorphisms (HTR2A -1438G>A, 102T>C, H452Y; DRD2 -141delC, Taq I A; COMT V158M) were genotyped. The diplotype configuration for each individual was estimated by the maximum-likelihood method. Multiple linear regressions were used to analyze the effects of these haplotypes/genotype and other prognostic factors on PANSS scale performance. After adjustment for the effects of patient-related variables, HTR2A diplotype and COMT genotype, as well as other potential prognostic factors, did not significantly influence the clinical performance. A DRD2 haplotype tended to correlate with better clinical performance. Compared with patients who had Ins-A2/Ins-A2 diplotype (n=25), PANSS total scores of patients with Ins-A2/Del-A1 diplotype (n=10) showed 40% greater improvement (P=0.03). The PANSS total scores of patients with HTR2A A-T/A-T diplotype (n=22) tended to show 15% worse improvement compared with A-T/G-C diplotype (n=33) (P=0.06). These results should be treated with caution because of limitations due to small sample size, heterogeneity of patients with respect to past antipsychotic use history, and no correction for multiple corrections. However, the present findings generate important hypotheses in a sample of Japanese schizophrenia patients that may lay the foundation for future pharmacogenomics investigations in other populations.

Clinical features of psychotic disorders and polymorphisms in HT2A, DRD2, DRD4, SLC6A3 (DAT1), and BDNF: a family based association study

Schizophrenia is clinically heterogeneous and multidimensional, but it is not known whether this is due to etiological heterogeneity. Previous studies have not consistently reported association between any specific polymorphisms and clinical features of schizophrenia, and have primarily used case-control designs. We tested for the presence of association between clinical features and polymorphisms in the genes for the serotonin 2A receptor (HT2A), dopamine receptor types 2 and 4, dopamine transporter (SLC6A3), and brain-derived neurotrophic factor (BDNF). Two hundred seventy pedigrees were ascertained on the basis of having two or more members with schizophrenia or poor outcome schizoaffective disorder. Diagnoses were made using a structured interview based on the SCID. All patients were rated on the major symptoms of schizophrenia scale (MSSS), integrating clinical and course features throughout the course of illness. Factor analysis revealed positive, negative, and affective symptom factors. The program QTDT was used to implement a family-based test of association for quantitative traits, controlling for age and sex. We found suggestive evidence of association between the His452Tyr polymorphism in HT2A and affective symptoms (P = 0.02), the 172-bp allele of BDNF and negative symptoms (P = 0.04), and the 480-bp allele in SLC6A3 (= DAT1) and negative symptoms (P = 0.04). As total of 19 alleles were tested, we cannot rule out false positives. However, given prior evidence of involvement of the proteins encoded by these genes in psychopathology, our results suggest that more attention should be focused on the impact of these alleles on clinical features of schizophrenia.

Childhood inattention and dysphoria and adult obesity associated with the dopamine D4 receptor gene in overeating women with seasonal affective disorder

There is significant evidence that altered dopamine activity plays a role in seasonal affective disorder (SAD). The current study examined three separate genetic hypotheses for SAD related to the 7-repeat allele (7R) of the dopamine-4 receptor gene (DRD4), a variant associated with decreased affinity for dopamine. We examined the possible contribution of 7R to the overall expression of SAD, attention deficit disorder (ADD) comorbidity, and body weight regulation. As part of an ongoing genetic study of increased eating behavior and mood in female subjects, 108 women with winter SAD and carbohydrate craving/weight gain were administered the Wender-Utah Rating Scale to measure childhood ADD symptomatology, and a questionnaire to assess maximal lifetime body mass index (BMI). To test for an association between 7R and the categorical diagnosis of SAD, the transmission disequilibrium test (TDT) was used in a subsample of probands providing familial DNA. Standard parametric tests were used to compare childhood ADD symptoms and maximal lifetime BMI across the two genotypic groups defined by the presence or absence of 7R. The TDT found no initial evidence for an association between 7R and the categorical diagnosis of SAD. However, 7R carriers reported significantly greater inattention and dysphoria in childhood (p=0.01 and 0.001, respectively) and a higher maximal lifetime BMI (p=0.007) than did probands without this allele. Furthermore, excluding probands with extreme obesity (maximal BMI >40), a strong correlation was found linking childhood inattentive symptoms and maximal lifetime BMI (r=0.35, p=0.001). In overeating women with SAD, the 7R allele of DRD4 may be associated with a unique developmental trajectory characterized by attentional deficits and dysphoria in childhood and mild to moderate obesity in adulthood. This developmental course may reflect different manifestations of the same underlying vulnerability related to central dopamine dysfunction. Given the possibility of population stratification when studying genotype/phenotype relationships, future use of genomic controls and replication of our findings in other overeating and/or ADD populations are needed to confirm these initial results.

Re-screening serotonin receptors for genetic variants identifies population and molecular genetic complexity

We have re-screened the genes for the 5-HT1A, 5-HT2A, 5-HT2C, and 5-HT7 serotonin receptors for genetic variants in a large African-American and Caucasian-American population sample. We have identified eight novel variants in these genes including four that are predicted to cause amino acid substitutions. These variants are additional candidates for association studies of behavioral disorders such as depression and schizophrenia as well as quantitative personality traits. We have also detected some, but not all, previously identified variants in these genes suggesting that many previously identified variants are unique to specific populations. The results of this study, and previous screens of serotonin receptors, demonstrate that the genes for serotonin receptors display marked population and molecular genetic complexity. These levels of complexity may have a substantial effect on genetic association studies of human behavioral variability related to these genes. We discuss the implications of these findings and propose methods to address complexity in genetic association studies.

Serotonin transporter missense mutation associated with a complex neuropsychiatric phenotype

Two common serotonin transporter (SERT) untranslated region gene variants have been intensively studied, but remain inconclusively linked to depression and other neuropsychiatric disorders. We now report an uncommon coding region SERT mutation, Ile425Val, in two unrelated families with OCD and other serotonin-related disorders. Six of the seven family members with this mutation had OCD (n=5) or obsessive-compulsive personality disorder (n=1) and some also met diagnostic criteria for multiple other disorders (Asperger's syndrome, social phobia, anorexia nervosa, tic disorder and alcohol and other substance abuse/dependence). The four most clinically affected individuals--the two probands and their two slbs--had the I425V SERT gene gain-of-function mutation and were also homozygous for 5'-UTR SERT gene variant with greater transcriptional efficacy.

A functional genetic variation of the 5-HT2a receptor affects human memory

Human memory capacity is highly variable across individuals and is influenced by both genetic and environmental factors. A roughly 50% heritability estimate indicates that naturally occurring genetic variations have an important impact on this cognitive ability. Therefore, we investigated a functional variation of a memory-related serotonin receptor in 349 healthy young volunteers, and found 21% poorer memory performance in subjects with the rare variant.

Seasonal affective disorder: an overview

Seasonal Affective Disorder (SAD) is a condition of regularly occurring depressions in winter with a remission the following spring or summer. In addition to depressed mood, the patients tend to experience increased appetite and an increased duration of sleep during the winter. SAD is a relatively common condition, affecting 1-3% of adults in temperate climates, and it is more prevalent in women. The pathological mechanisms underlying SAD are incompletely understood. Certain neurotransmitters have been implicated; a dysfunction in the serotonin system in particular has been demonstrated by a variety of approaches. The role of circadian rhythms in SAD needs to be clarified. The phase-delay hypothesis holds that SAD patients' circadian rhythms are delayed relative to the sleep/wake or rest/activity cycle. This hypothesis predicts that the symptoms of SAD will improve if the circadian rhythms can be phase-advanced. There is some experimental support for this. SAD can be treated successfully with light therapy. In classical light therapy, the SAD sufferer sits in front of a light box, exposed to 2000-10,000 lux for 30-120 min daily during the winter. Other forms of light treatments, pharmacotherapy, and other therapies are currently being tested for SAD.

Serotonergic system and attention deficit hyperactivity disorder (ADHD): a potential susceptibility locus at the 5-HT(1B) receptor gene in 273 nuclear families from a multi-centre sample

Attention deficit hyperactivity disorder (ADHD) is a highly heritable and heterogeneous disorder, which usually becomes apparent during the first few years of childhood. Imbalance in dopamine neurotransmission has been suggested as a factor predisposing to ADHD. However, evidence has suggested an interaction between dopamine and serotonin systems in the pathophysiology of the disorder. Studies using selective agonists of the different 5-HT receptors microinjected into selected brain structures have shown a positive modulating effect on the functional activities of the mesotelencephalic dopaminergic system. This suggests that some of the genetic predisposition to ADHD might be due to DNA variation at serotonin system genes. In this study, we investigated polymorphisms in HTR(1B) and HTR(2A) (which encode the serotonin receptors 5-HT(1B) and 5-HT(2A) respectively) in a European ADHD sample. Using haplotype based haplotype relative risk (HHRR) and transmission disequilibrium test (TDT) analyses, we observed significant preferential transmission of the allele 861G of the HTR(1B) in the total sample (for HHRR; chi(2) = 7.4, P = 0.0065 and TDT; (chi(2) = 6.4, P = 0.014). Analysis of HTR(2A) failed to reveal evidence of association or linkage between the His452Tyr polymorphism and ADHD in the total sample. However, a significantly increased transmission of the allele 452His was observed in the Irish sample alone (chi(2) = 4.9, P = 0.026). These preliminary data suggest an important role for the serotonin system in the development of ADHD. Further studies, preferentially including different ethnic groups are required to substantiate these findings.

Polymorphism of the serotonin-2A receptor gene (HTR2A) associated with childhood attention deficit hyperactivity disorder (ADHD) in adult women with seasonal affective disorder

INTRODUCTION

Several lines of research point to a possible overlap between seasonal affective disorder (SAD) and attention deficit hyperactivity disorder (ADHD), particularly in females. There is also emerging evidence that variation of the 5-HT2A receptor gene (HTR2A) contributes to both SAD and ADHD. The current study investigated whether variation in HTR2A was associated with symptoms of childhood ADHD in adult women with SAD.

METHOD

Sixty-six women with SAD were administered the Wender-Utah Rating Scale (WURS), which retrospectively assesses childhood ADHD, as part of an ongoing genetic study of SAD. WURS scores were compared across the three genotypic groups defined by the T102C polymorphism of HT2RA.

RESULTS

Analysis of variance indicated a significant difference in mean 25-item WURS scores across the three genotypic groups (p = 0.035). Post-hoc tests revealed that the C/C genotypic group had a significantly higher mean score than both the T/T group and T/C group. Based on previously established WURS criteria, 38% of subjects with the C/C genotype, and none with the T/T genotype, had scores consistent with childhood ADHD.

LIMITATIONS

The current sample size is small, and childhood ADHD diagnoses were based on retrospective recall.

CONCLUSION

These preliminary results suggest a possible association between variation in HTR2A, childhood ADHD, and the later development of SAD in women.

Human genetic variation and mental disorders

Despite extensive research, our knowledge of structural or functional pathology of severe mental disorders such as schizophrenia and major affective disorders is limited. The only etiological factor with reasonably firm foundation is inheritance, as evidenced by family, twin and adoption studies, however, the molecular basis of this heritability is not established yet. In the absence of clear knowledge about the biological substrate for these psychiatric disorders all the genes expressed in the human brain are potential candidate genes. Association studies analyze genetic variants (polymorphisms) in genes with presumed functional significance in the pathophysiology of the disease (candidate genes). These genetic studies compare the frequency of the hypothetical risk variant in people affected by the disease and in healthy control representatives of the same population. Also, simplex families with an affected child (trios) or with discordant affected offspring (quadruplets), can be used in the association studies. This strategy constitutes a tool to identify the small and moderate effects of genes in these complex phenotypes. Likewise, these kinds of studies could be useful to explain the effect of genes in some specific traits and symptoms present in functional psychoses. Some of our own results on serotoninergic system genes and major depression are included in this chapter as an example of case-control association developed studies in mental disorders.

Serotonin 5-HT(2A) receptor gene polymorphism, 5-HT(2A) receptor function and personality traits in healthy subjects: a negative study

BACKGROUND

Central serotonin-2A (5-HT(2A)) receptor dysfunction is regarded as an important factor in the etiology of affective disorders. The relations between some personality traits and the vulnerability of affective disorders are also implicated. Moreover, there are several reports which describe the association between 5-HT(2A) receptor gene polymorphisms and mental disorders. We therefore examined the relationship between personality traits, the 5-HT(2A) receptor function, and 5-HT(2A) receptor gene polymorphisms.

METHODS

5-HT-induced intraplatelet calcium (Ca) mobilization, 5-HT(2A) receptor gene polymorphisms (A-1438G, T102C, T516C, C1340T, C1354T), and Temperament and Character Inventory (TCI) scores were examined in 133 healthy subjects.

RESULTS

Neither 5-HT-induced Ca mobilization nor 5-HT(2A) receptor gene polymorphisms (A-1438G, T102C) appear to be associated with seven personality dimensions including Harm Avoidance. There was no significant difference in the Ca response among the subjects with -1438A/A, A/G and G/G genotypes. Since the appearance of the other types of the 5-HT(2A) receptor gene polymorphisms (T516C, C1340T and C1354T) was quite rare in our sample, we were unable to examine the relationship between these polymorphisms, and the TCI score or the Ca response.

LIMITATIONS

Our failure to find a significant association may reflect the false negative results due to the small sample size and low statistical power. Further studies in depressed patients may clarify the complicated relationship between personality traits and the vulnerability of affective disorders.

CONCLUSIONS

Personality traits detected by TCI may not be directly related to the 5-HT(2A) receptor function or 5-HT(2A) receptor gene polymorphism which may be involved in the vulnerability of affective disorders.

Association between 5HT2A receptor gene promoter region polymorphism and eating disorders in Japanese patients

BACKGROUND

Evidence from family and twin studies suggests a genetic contribution to the etiology of eating disorders (EDs). Recently, researchers have reported genetic associations between the MspI polymorphism (-1438A/G) of the promoter region of the 5HT2A receptor gene and EDs; however, reports of evidence against these findings make the association controversial.

METHODS

The authors examined the prevalence of the -1438A/G polymorphism of the 5HT2A receptor gene among 182 Japanese patients with EDs and 374 normal control subjects. Interactions of the association of this polymorphism with subtypes of anorexia nervosa (AN), bulimia nervosa (BN), and various clinical characteristics were also assessed.

RESULTS

In contrast to previous studies reporting elevated A allele frequencies in patients with AN, the G allele had a significantly higher frequency in patients with BN but not in patients with AN, than in control subjects. Examination of the interactions revealed that the presence of the binge eating and/or purging behavior and comorbid borderline personality disorder (BPD) tended to be associated with increased frequency of the G allele.

CONCLUSIONS

Though preliminary, these results can be interpreted as suggesting that the G allele of the 5HT2A receptor gene -1438A/G polymorphism may be associated with pathological features that EDs and BPD have in common, especially disinhibition in eating behavior and personality trait.

Serotonergic polymorphisms in patients suffering from alcoholism, anxiety disorders and narcolepsy

1. Alterations in the serotonergic neurotransmission have been frequently described for patients suffering from alcoholism, anxiety disorders and narcolepsy. 2. The authors tested for association of the 5-HT2A receptor polymorphism (T102C) and the intron 7 tryptophan hydroxylase (TPH) polymorphism (A218C) among 176 alcohol dependent patients, 35 patients with panic disorder, 50 patients with generalized anxiety disorder, 55 patients with narcolepsy and 87 healthy controls. 3. Allele and genotype frequencies of the 5-HT2A receptor polymorphism (T102C), the intron 7 TPH polymorphism (A218C) were almost similar between the patients suffering from alcohol dependence, panic disorder, generalized anxiety disorder and narcolepsy. 4. There was no association between the 5-HT2A receptor polymorphism (T102C), the intron 7 TPH (A218C) polymorphisms and alcohol dependence, panic disorder, generalized anxiety disorder and narcolepsy in our subsets of German patients.

Seasonal affective disorder and serotonin-related polymorphisms

Disturbances in central serotonergic systems have been hypothesized to be involved in seasonal affective disorder (SAD). Association between SAD and the shorter allele of the serotonin transporter promoter repeat length polymorphism (5-HTTLPR) has been reported in an American sample. We have genotyped 82 SAD patients and 82 healthy controls from Sweden, Finland, and Germany for this and five other polymorphisms in the genes coding for serotonin receptors 5-HT2A and 5-HT2C, tryptophan hydroxylase and white. No associations with SAD or seasonality (seasonal variations in mood and behavior) were detected. Although minor effects cannot be excluded, our results suggest that these polymorphisms do not play a major role in the pathogenesis of SAD in the northern European population.

Variability in the 5-HT(2A) receptor gene is associated with seasonal pattern in major depression

The 102-T/C polymorphism of the 5-HT(2A) receptor gene was analysed in 159 patients with major depression and 164 unrelated and healthy controls using a case-control design. Allele and genotype frequencies did not differ between cases and controls. No differences according to sex, age of onset, melancholia, suicidal behaviour or family history of psychiatric illness were found. However, genotype distributions significantly differed between patients with seasonal pattern in their episodes (MDS) and patients with no seasonal pattern (N-MDS) (chi(2) = 10.63; P = 0.004). A seasonal pattern was 7.57 times more frequent in 102C-allele carriers than in 102T homozygous (95.1% of patients MDS carried 102C-allele vs 72% of patients N-MDS (chi(2) = 9.45, df=1, P = 0.002; OR = 7.57 (95% CI: 1.65--48.08)). These results suggest that variation in the 5-HT2A receptor gene may play a role in the development of major depression with seasonal pattern and support the existence of a genetic and etiological heterogeneity underlying the diagnosis of major depression.

Association between the serotonin 2A receptor gene and tardive dyskinesia in chronic schizophrenia

Tardive dyskinesia (TD) is a long-term adverse effect of antipsychotic drugs that are dopamine D2 receptor blockers.(1) Serotonin receptor antagonism has been proposed as a common mechanism contributing to the low extrapyramidal effects profile of atypical antipsychotic drugs.(2) We examined the association of three polymorphisms in the 5-HT2A receptor gene (HTR2A) with TD susceptibility--T102C(3) and his452tyr(4) in the coding region and A-1438G(5) in the promoter--in matched schizophrenia patients with (n = 59, SCZ-TD-Y) and without TD (n = 62, SCZ-TD-N) and normal control subjects (n = 96). The T102C and the A-1438G polymorphisms are in complete linkage disequilibrium but not his452tyr. There was a significant excess of 102C and -1438G alleles (62.7%) in the SCZ-TD-Y patients compared to SCZ-TD-N patients (41.1%) and controls (45.9%; chi(2) = 12.8, df = 2, P = 0.002; SCZ-TD-Y vs SCZ-TD-N, chi(2) = 11.4, df = 1, P = 0.0008, OR 2.41, 95% CI 1.43-3.99) and of 102CC and -1438GG genotypes (SCZ-TD-Y 42.4%, SCZ-TD-N, 16.1%, controls 20.8%, chi(2) = 13.3, df = 4, P = 0.01). The 102CC and the -1438GG genotypes were associated with significantly higher AIMS trunk dyskinesia scores (F = 3.9; df = 2, 116; P = 0.02) and more incapacitation (F = 5.0; df = 2, 115; P = 0.006). The his452tyr polymorphism showed no association with TD. These findings suggest that the 5-HT2A receptor gene is significantly associated with susceptibility to TD in patients with chronic schizophrenia. Previously reported association of the T102C and A-1438G polymorphisms with schizophrenia(6) may reflect association of a sub-group of patients with a susceptibility to abnormal involuntary movements related to antipsychotic drug exposure.

Pharmacogenetics and the serotonin system: initial studies and future directions

Serotonin (5-hydroxytryptamine, 5-HT) appears to play a role in the pathophysiology of a range of neuropsychiatric disorders, and serotonergic agents are of central importance in neuropharmacology. Genes encoding various components of the 5-HT system are being studied as risk factors in depression, schizophrenia, obsessive-compulsive disorder, aggression, alcoholism, and autism. Recently, pharmacogenetic research has begun to examine possible genetic influences on therapeutic response to drugs affecting the serotonin system. Genes regulating the synthesis (TPH), storage (VMAT2), membrane uptake (HTT), and metabolism (MAOA) of 5-HT, as well as a number of 5-HT receptors (HTR1A, HTR1B, HTR2A, HTR2C, and HTR5A), have been studied and this initial research is reviewed here. After a brief introduction to serotonin neurobiology and a general discussion of appropriate genetic methodology, each of the major 5-HT-related genes and their encoded proteins are reviewed in turn. For each gene, relevant polymorphisms and research on functional variants are discussed; following brief reviews of the disorder or trait association and linkage studies, pharmacogenetic studies performed to date are covered. The critical and manifold roles of the serotonin system, the great abundance of targets within the system, the wide range of serotonergic agents-available and in development-and the promising preliminary results suggest that the serotonin system offers a particularly rich area for pharmacogenetic research.

Evidence for the serotonin HTR2A receptor gene as a susceptibility factor in attention deficit hyperactivity disorder (ADHD)

A recent study demonstrated that treatment of hyperactive mice with psychostimulants and serotonergic agents produced a calming effect that was dependent on serotonergic neurotransmission and was not associated with any changes in extracellular dopamine levels. The complex interaction between the serotonergic and dopaminergic neurotransmitter systems suggests that a balance between the two systems may be necessary for mediating hyperactive behaviour. Defects in serotonin system genes, therefore, may disrupt normal brain serotonin function causing an imbalance between these neurotransmitter systems leading to the development of attention deficit hyperactivity disorder (ADHD). Using the transmission disequilibrium test (TDT), the current study assesses for linkage disequilibrium between polymorphisms in the serotonin HTR2A receptor gene and ADHD. One hundred and fifteen families with a total of 143 children diagnosed with ADHD (DSM-IV) were genotyped for the His452 Tyr and the T102C polymorphisms in the serotonin HTR2A receptor gene. TDT analysis revealed a preferential transmission of the 452Tyr allele to the affected offspring (P = 0.03), suggesting linkage disequilibrium of this polymorphism with ADHD. This may open a new door in ADHD molecular genetics research, expanding the existing view of a catecholaminergic hypothesis to include a serotonergic hypothesis and should help elucidate the complex interplay among the neurotransmitter systems in the etiology of ADHD.

Association of polymorphism of serotonin 2A receptor gene with suicidal ideation in major depressive disorder

There is evidence indicating that density of 5-HT2A receptors is altered in brain regions of depressed suicide victims and in platelets of suicidal subjects with major depression or schizophrenia. Recent studies have also shown an association between the allele C of 102T/C polymorphism in the 5-HT2A receptor gene and schizophrenia. The present investigation tested the hypothesis that the observed changes in 5-HT2A receptor density in platelets of patients with major depression are a trait rather than state phenomenon and are associated with the 102 C allele in 5-HT2A receptor gene in a sample of 120 patients with major depression and a group of 131 control subjects comparable with respect to age, sex, and ethnic background. The allele and genotype frequencies of 102T/C polymorphism in 5-HT2A receptor gene were compared between patients and control subjects and between suicidal and non-suicidal patient groups. The major finding of this study was a significant association between the 102 C allele in 5-HT2A receptor gene and major depression, chi(2) = 4.5, df = 1, P = 0.03, particularly in patients with suicidal ideation, chi(2) = 8.5, df = 1, P < 0.005. Furthermore, we found that patients with a 102 C/C genotype had a significantly higher mean HAMD item 3 score (indication of suicidal ideation) than T/C or T/T genotype patients. Our results suggest that the 102T/C polymorphism in 5-HT2A receptor gene is primarily associated with suicidal ideation in patients with major depression. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:56-60, 2000.

Identification and analysis of new sequence variants in the human tryptophan hydroxylase (TpH) gene

The tryptophan hydroxylase (TpH) gene codes for the rate-limiting enzyme in serotonin biosynthesis. It is one of the major candidate genes for psychiatric and behavioral disorders. A polymorphism in TpH intron 7 has been shown to be associated with suicidal attempts, aggressive behavior and psychiatric illnesses. By systematically screening the TpH genomic sequence, we identified and confirmed an earlier report of four variants in the promoter region and localized six new sequence variants, ie two in intron 1b, one in exon 1c, one in intron 8, one in intron 9 and a microsatellite in the 3' region, 5687 bp downstream of the last exon 11. We analyzed these polymorphisms, as well as the one in intron 7, by Single Strand Conformation Analysis, microsatellite or restriction analysis in a collection of 175 West European Caucasian healthy subjects. The four variants in the promoter region are in complete linkage disequilibrium (frequencies of G-T-G-T and T-C-A-G haplotypes are 0. 41 and 0.59, respectively). Deletion of GTT in intron 1b is rare (0. 7%) and so not informative. The rarer allele T of intron 1b polymorphism T3792A has a frequency of 0.34 and is in partial linkage disequilibrium with the more common alleles of intron 7, 8 and 9. The polymorphisms of these three introns are in complete linkage disequilibrium and the frequencies of haplotypes A-T-C and C-C-T are 0.36 and 0.64 respectively. We detected 10 different alleles in the microsatellite localized in the 3' region; allele '194' is in partial linkage disequilibrium with haplotype A-T-C of introns 7, 8, and 9. Analysis of these different polymorphisms will constitute an important tool for future studies between the TpH gene and psychiatric disorders. Molecular Psychiatry (2000) 5, 49-55.

Biological phenotypes associated with individuals at high risk for developing alcohol-related disorders: Part 1

This article reviews the results of studies concerning particular classes of biological phenotypes that may have relevance for alcohol dependence. Broadly defined, these classes include brain neurotransmitter systems and neuroelectric potentials. Evidence is presented concerning genotypic variation in alcoholics and high-risk relatives suggesting that the etiology of alcoholism and other addictive diseases is mediated in part through suboptimal neurotransmitter functioning. Research opportunities are offered with respect to specific candidate genes that have been cloned from these neurotransmitter systems that could be most fully utilized in family-based genetic analyses. Additional evidence is offered, suggesting that characteristics of particular neuroelectric potentials (e.g. the amplitude of the P300 component of the event-related potential) may provide another dimension of potential markers that could be used to identify children at risk. Finally, methodological considerations specific to high risk studies are discussed. Among these are the need to include a plan for studying more severe cases of alcohol dependence that are relatively uncomplicated by other major psychiatric disorders. Plans for long-term follow-up of children at highest risk for developing the disorder should also be included. Multiple domains of inquiry should not be viewed as "unfocused" but rather as an economical means for utilizing highly characterized samples of individuals meeting rigorous research criteria.