Association study of the 5-HT6 receptor gene in schizophrenia

SLC6A3, HTR2C and HTR6 Gene Polymorphisms and the Risk of Haloperidol-Induced Parkinsonism

Antipsychotic-induced parkinsonism (AIP) is the most common type of extrapyramidal side effect (EPS), caused by the blockage of dopamine receptors. Since dopamine availability might influence the AIP risk, the dopamine transporter (DAT) and serotonin receptors (5-HTRs), which modulate the dopamine release, may be also involved in the AIP development. As some of the individual differences in the susceptibility to AIP might be due to the genetic background, this study aimed to examine the associations of SLC6A3, HTR2C and HTR6 gene polymorphisms with AIP in haloperidol-treated schizophrenia patients. The Extrapyramidal Symptom Rating Scale (ESRS) was used to evaluate AIP as a separate entity. Genotyping was performed using a PCR, following the extraction of blood DNA. The results revealed significant associations between HTR6 rs1805054 polymorphism and haloperidol-induced tremor and rigidity. Additionally, the findings indicated a combined effect of HTR6 T and SLC6A3 9R alleles on AIP, with their combination associated with significantly lower scores of ESRS subscale II for parkinsonism, ESRS-based tremor or hyperkinesia and ESRS subscales VI and VIII. These genetic predictors of AIP could be helpful in better understanding its pathophysiology, recognizing the individuals at risk of developing AIP and offering personalized therapeutic strategies for the patients suffering from this EPS.

A review of genetic alterations in the serotonin pathway and their correlation with psychotic diseases and response to atypical antipsychotics

Serotonin is a neurotransmitter that plays a predominant role in mood regulation. The importance of the serotonin pathway in controlling behavior and mental status is well recognized. All the serotonin elements - serotonin receptors, serotonin transporter, tryptophan hydroxylase and monoamine oxidase proteins - can show alterations in terms of mRNA or protein levels and protein sequence, in schizophrenia and bipolar disorder. Additionally, when examining the genes sequences of all serotonin elements, several single nucleotide polymorphisms (SNPs) have been found to be more prevalent in schizophrenic or bipolar patients than in healthy individuals. Several of these alterations have been associated either with different phenotypes between patients and healthy individuals or with the response of psychiatric patients to the treatment with atypical antipsychotics. The complex pattern of genetic diversity within the serotonin pathway hampers efforts to identify the key variations contributing to an individual's susceptibility to the disease. In this review article, we summarize all genetic alterations found across the serotonin pathway, we provide information on whether and how they affect schizophrenia or bipolar disorder phenotypes, and, on the contribution of familial relationships on their detection frequencies. Furthermore, we provide evidence on whether and how specific gene polymorphisms affect the outcome of schizophrenic or bipolar patients of different ethnic groups, in response to treatment with atypical antipsychotics. All data are discussed thoroughly, providing prospective for future studies.

Design, synthesis and pharmacological evaluation of indolylsulfonamide amines as potent and selective 5-HT6 receptor antagonists

A series of N'-[3-(indole-1-sulfonyl) aryl]-N,N-dimethyl ethane-1,2-diamines and N'-[3-(indole-1-sulfonyl) aryl]-N,N-dimethyl propane-1,3-diamines was designed and synthesized as 5-HT6 receptor ligands. These compounds, when screened in a functional reporter gene-based assay, displayed potent antagonistic activity with Kb values in the range of 1.8-60 nM. The lead compound 9y has shown good ADME surrogate properties, acceptable pharmacokinetic profile and is active in animal models of cognition like novel object recognition test and Morris water maze. It was selected for detailed profiling.

Serotonin 6 receptor gene and schizophrenia: case-control study and meta-analysis

OBJECTIVES

Several lines of evidence suggest that genetic alterations in serotonin 6 (5-HT6) receptors might be associated with the pathophysiology of schizophrenia. We sought to assess the relationship between genotype alterations in 5-HT6 receptors and schizophrenia both in a case-control study and a meta-analysis.

METHODS

We conducted an association study of the 5-HT6 receptor gene (HTR6) in Japanese patients with schizophrenia (n = 836) and controls (n = 857). Five tagging single-nucleotide polymorphisms (SNPs), including rs1805054 (C267T) in HTR6, were selected. In addition, we carried out a meta-analysis between rs1805054, which has been examined in other studies, and schizophrenia, searching PubMed through August 2011.

RESULTS

There were no significant associations between the tagging SNPs in HTR6 and schizophrenia in any of the genotype models in both the simple and the multiple logistic regression analyses correcting for potential confounds. Similarly, no significant association was found in the all-marker haplotype multiple logistic regression analysis (p = 0.491). Moreover, in the meta-analysis of rs1805054, drawing data from five studies, including our own (schizophrenia patients = 1366, controls = 1376), rs1805054 was also not associated with schizophrenia.

CONCLUSIONS

Our results indicate that tagging SNPs in HTR6 may not play a role in the pathophysiology of schizophrenia.

Serotonin 6 receptor gene is associated with methamphetamine-induced psychosis in a Japanese population

BACKGROUND

Altered serotonergic neural transmission is hypothesized to be a susceptibility factor for psychotic disorders such as schizophrenia. The serotonin 6 (5-HT6) receptor is therapeutically targeted by several second generation antipsychotics, such as clozapine and olanzapine, and d-amphetamine-induced hyperactivity in rats is corrected with the use of a selective 5-HT6 receptor antagonist. In addition, the disrupted prepulse inhibition induced by d-amphetamine or phencyclidine was restored by 5-HT6 receptor antagonist in an animal study using rats. These animal models were considered to reflect the positive symptoms of schizophrenia, and the above evidence suggests that altered 5-HT6 receptors are involved in the pathophysiology of psychotic disorders. The symptoms of methamphetamine (METH)-induced psychosis are similar to those of paranoid type schizophrenia. Therefore, we conducted an analysis of the association of the 5-HT6 gene (HTR6) with METH-induced psychosis.

METHOD

Using five tagging SNPs (rs6693503, rs1805054, rs4912138, rs3790757 and rs9659997), we conducted a genetic association analysis of case-control samples (197 METH-induced psychosis patients and 337 controls) in the Japanese population. The age and sex of the control subjects did not differ from those of the methamphetamine dependence patients.

RESULTS

rs6693503 was associated with METH-induced psychosis patients in the allele/genotype-wise analysis. Moreover, this association remained significant after Bonferroni correction. In the haplotype-wise analysis, we detected an association between two markers (rs6693503 and rs1805054) and three markers (rs6693503, rs1805054 and rs4912138) in HTR6 and METH-induced psychosis patients, respectively.

CONCLUSION

HTR6 may play an important role in the pathophysiology of METH-induced psychosis in the Japanese population.

A quantitative structure-activity relationship study on serotonin 5-HT6) receptor ligands: indolyl and piperidinyl sulphonamides

The serotonin 5-HT(6) binding affinity of indolyl- and piperidinyl-sulphonamide derivatives has been analysed with topological and molecular features with DRAGON software. Analysis of the structural features in conjunction with the biological endpoints in combinatorial protocol in multiple linear regression (CP-MLR) led to the identification of 25 descriptors for modelling the activity. The study clearly suggested the role of an average Randic-type eigenvector-based index from adjacency matrix, VRA2, number of secondary aliphatic amines, nNHR, the sum of the topological distance between N and O, T(N...O), ring tertiary carbon atoms, nCrHR, and CH2RX type fragment, C-006, in a molecular structure to optimize the 5-HT(6) binding affinities of titled compounds. The PLS analysis confirmed the dominance of information content of CP-MLR identified descriptors for modelling the activity when compared with those of leftover ones.

Male specific association between the 5-HTR6 gene 267C/T SNP and suicide in the Portuguese population

Serotonergic system dysfunction has been implicated in the etiology of suicide. A large number of genetic studies have focused on the potential involvement of genes coding for components of serotonergic system in suicidal behavior. However, other genes belonging to this system remain to be investigated or have been poorly studied, as is the case of the 5-HT6 receptor (5-HTR6) gene. In this study, we investigated the potential association between the 5-HTR6 gene 267C/T SNP and suicide in a Portuguese population. Blood samples were collected from 179 suicide victims and 189 controls. Genotypes for the 5-HTR6 gene 267C/T SNP were obtained with the restriction enzyme Rsa I. A tendency was found for genotype association between this polymorphism and suicide, but the differences were not statistically significant (chi(2)=5.374, df=2, p=0.068). However, a gender-specific association was detected when comparing the genotype distribution between male suicide victims and male controls (chi(2)=6.988, df=2, p=0.030), suggesting that this SNP might have a role in the etiology of suicide in male subjects in the Portuguese population.

Increased impulsivity and disrupted attention induced by repeated phencyclidine are not attenuated by chronic quetiapine treatment

Atypical antipsychotic medications differ in how effectively they attenuate cognitive and other deficits in schizophrenia. The present study aimed to explore whether quetiapine, an atypical antipsychotic medication, would reverse disruptions of performance in the 5-choice serial reaction time task (5-CSRTT), a test of attention and impulsivity, induced by repeated administration of the psychotomimetic phencyclidine (PCP). In confirmation of previous findings, repeated PCP administration (2 mg/kg, s.c., 30 min before behavioral testing, for 2 consecutive days, followed by a 2-week PCP-free period and then 5 consecutive days of PCP treatment) increased premature responding (impulsivity), decreased accuracy (attention), and increased response latencies (processing speed) and timeout responding (impulsivity/cognitive inflexibility). Chronic quetiapine (5 or 10 mg/kg/day, s.c.) did not attenuate these PCP-induced disruptions in performance, while at the highest dose used, quetiapine disrupted 5-CSRTT performance in the absence of PCP treatment and tended to exacerbate the PCP-induced increase in premature responding. Considering that clozapine, another atypical antipsychotic, was shown previously to reverse PCP-induced deficits in the same task [Amitai N, Semenova S, Markou A. Cognitive-disruptive effects of the psychotomimetic phencyclidine and attenuation by atypical antipsychotic medications in rats. Psychopharmacology (Berl) 2007;193:521-37], the present findings demonstrate differences between clozapine and quetiapine in their effectiveness on schizophrenia-like cognitive deficits and impulsivity that may be attributable to their different receptor affinity profiles.

Association of unipolar depression with gene polymorphisms in the serotonergic pathways in Han Chinese

OBJECTIVE

The present study aims to investigate the association of unipolar depression (UPD) with six serotonergic gene polymorphisms in Han Chinese.

METHODS

One hundred and thirty-two UPD patients and 180 healthy controls were genotyped for polymorphisms of six serotonergic genes, including tryptophan hydroxylase (TPH1 A218C), serotonin transporter promoter region (5-HTTLPR), serotonin receptor 2A (5-HT2AR -1438G/A), serotonin receptor 2C (5-HT2CR Cys23Ser), serotonin receptor 6 (5-HT6R C267T) and serotonin receptor 1Dβ (5-HT1DβR T371G). Symptomatic clusters were evaluated by the 24-item Hamilton Rating Scale for Depression (HAMD).

RESULTS

The frequencies of S/S genotype and S allele in 5-HTTLPR polymorphism were significantly higher in UPD patients than in healthy controls. There was a significant difference in distributions of genotypes in 5-HT2CR Cys23Ser polymorphism between UPD patients and control subjects, but the difference became no significant when the data were further stratified by gender. The patients with genotypes G/G and T/G of 5-HT1DβR T371G polymorphism had significantly lower scores of diurnal variation evaluated by HAMD than those with genotype T/T, while the patients with genotype T/G had significantly higher scores of hopelessness than those with genotypes G/G and T/T. There were no significant differences in genotypic and allelic distributions of TPH1 A218C, 5-HT2AR -1438G/A or 5-HT6R C267T polymorphisms between the case and control groups.

CONCLUSION

The study demonstrates that 5-HTTLPR and 5-HT2CR Cys23Ser polymorphisms might contribute to susceptibility of UPD, and the genotype T/T in 5-HT1DβR T371G polymorphism might be a risk factor for diurnal variation, while T/G might be a protective factor against hopelessness in Han Chinese populations.

A null mutation of the serotonin 6 receptor alters acute responses to ethanol

The anatomical distribution and pharmacology of serotonin 6 receptors (5-HT6Rs) implicate them as contributors to the serotonergic regulation of complex behavior. To complement the limited range of pharmacological tools available to examine 5-HT6R function, we have generated a mouse line bearing a constitutive null mutation of the 5-HT6R gene. No perturbations of baseline behavior were noted in a wide array of assays pertinent to multiple neurobehavioral processes. However, 5-HT6R mutant mice demonstrated reduced responses to the ataxic and sedative effects of ethanol. No differences in ethanol metabolism were evident between wild-type and 5-HT6R mutant mice. These findings implicate 5-HT6Rs in the serotonergic modulation of responses to ethanol.

No association of 5-HT2C, 5-HT6, and tryptophan hydroxylase-1 gene polymorphisms with personality traits in the Japanese population

Serotonin 2C receptor (5-HT(2C)), serotonin 6 receptor (5-HT(6)), and tryptophan hydroxylase-1 (TPH1) genes could be candidates for personality-related genes considering the role of serotonin in various mental functions and behavior. However, a limited number of studies have investigated the association between these genes and personality traits. In the present study, we investigated the three serotonin-related genes, 5-HT(2C), 5-HT(6), and TPH1 genes, in relation to personality traits in the Japanese population. The Cys23Ser polymorphisms in the 5-HT(2C) gene, the 267T/C polymorphism of the 5-HT(6) gene, and the 779A/C polymorphisms in the TPH1 gene were genotyped in 253 healthy Japanese subjects. Personality traits were evaluated by using the Revised NEO Personality Inventory (NEO PI-R) and the State-Trait Anxiety Inventory (STAI). As a result, no significant association was observed between the polymorphisms and the NEO PI-R or the STAI scores. The present results did not provide evidence for the association between the three serotonin-related genes and personality traits. The genes might not have major role in the development of personality traits, although further investigation with larger sample size may be recommended for conclusion.

5-HT6 receptors: a novel target for cognitive enhancement

Over the past decade, there has been increasing interest in the role of serotonin 6 (5-HT6) receptors in higher cognitive processes such as memory. Polymorphisms of the 5-HT6 receptor have been implicated in syndromes that affect cognition, such as schizophrenia and dementia. Manipulation of 5-HT6 receptor activity alters the transmission of several neurotransmitters important in memory: acetylcholine and glutamate, as well as dopamine, ã-aminobutyric acid (GABA), epinephrine (E), and norepinephrine (NE). Several 5-HT6 antagonists have been developed, advancing the understanding of the relationship between 5-HT6 blockade and memory consolidation in diverse learning paradigms. There is also evidence that 5-HT6 receptor activity affects anxiety behaviors and may be involved in the pathophysiology of schizophrenia. Several clinically useful atypical antipsychotics and antidepressants have 5-HT6 affinity, but recently developed selective 5-HT6 receptor antagonists may present attractive, new therapeutic options for several types of disease states.

Lack of an association between 5-HT receptor gene polymorphisms and suicide victims

An association between serotonergic dysfunction in the brain and suicidal behavior has previously been suggested. The high affinity of some antipsychotic and antidepressant drugs to serotonin 6 (5-HT6) receptors, and the predominant localization of 5-HT6 receptors in some limbic regions, suggest that 5-HT6 receptors play a role in the pathogenesis of suicide. The objective of the present study was to examine the association between suicide victims and two polymorphisms of the 5-HT6 receptor gene: a biallelic polymorphism (267C/T) in exon 1 and a trinucleotide repeat polymorphism ([GCC](2/3)) in the 5'-upstream region of the gene. The two polymorphisms were genotyped in 163 suicide victims and 166 controls, and the distribution of genotype and allele frequencies between the two groups were compared. Haplotype frequencies of these two polymorphisms were estimated from genotypic data by the maximum-likelihood method. In both polymorphisms, there were no significant differences in genotype or allele frequencies between the suicide victims and the controls. Moreover, there were no significant differences in the haplotype distributions of these polymorphisms between the two groups. These findings suggest that it is unlikely that the 5-HT6 receptor gene is involved in the susceptibility to suicide.

Medicinal Chemistry Driven Approaches Toward Novel and Selective Serotonin 5-HT6Receptor Ligands

Based on a medicinal chemistry guided hypothetical pharmacophore model, novel series of indolyl sulfonamides have been designed and prepared as selective and high-affinity serotonin 5-HT(6) receptor ligands. Furthermore, based on a screening approach of a discovery library, a series of benzoxazinepiperidinyl sulfonamides were identified as selective 5-HT(6) ligands. Many of the compounds described in this paper possess excellent affinities, displaying pK(i) values greater than 8 (some even >9) and high selectivities against a wide range (>50) of other CNS relevant receptors. First, structure-affinity relationships of these ligands are discussed. In terms of functionality, high-affinity antagonists, as well as agonists and even partial agonists, were prepared. Compounds 19c and 19g represent the highest-affinity 5-HT(6) agonists ever reported in the literature. These valuable tool compounds should allow for the detailed study of the role of the 5-HT(6) receptor in relevant animal models of disorders such as cognition deficits, depression, anxiety, or obesity.

Family-based association study of the serotonin-6 receptor gene (C267T polymorphism) in schizophrenia

The expression of serotonin type 6 receptor (5-HT(6)) in limbic and cortical regions of the brain, and its high affinity for atypical antipsychotics suggest that its encoding gene may play a role in the pathogenesis of schizophrenia. We firstly performed a meta-analysis of the C267T polymorphism of the 5-HT(6) gene in schizophrenia, based on four different case/control studies, and showed that the allelic distribution is not significantly different between patients and controls, even when taking into account the role of between samples heterogeneity. We then recruited 103 trios (patients with Diagnostic and Statistical Manual Mental Disorders, 4th ed. (DSM-IV) diagnosis of schizophrenia and their parents), and investigated the C267T polymorphism of the 5-HT(6) receptor gene with regard to family-based association study approach (haplotype relative risk (HRR) and transmission disequilibrium test (TDT)). We found no excess of transmission of one allele from the parents to their affected children, using the HRR (P = 0.60), as well as no evidence for linkage between C267T polymorphism and schizophrenia, using the TDT (P = 0.71). Furthermore, the 267T allele frequency was comparable in the different subgroups defined on age at onset, family history of schizophrenia, treatment response, and subtypes of patients based on positive versus negative predominant symptoms. These data do not support the idea that the 5-HT(6) receptor gene plays a major role in the etiopathogenesis of schizophrenia.

An assessment of the effects of serotonin 6 (5-HT6) receptor antagonists in rodent models of learning

Antagonists of serotonin 6 (5-HT6) receptors have been reported to enhance cognition in animal models of learning, although this finding has not been universal. We have assessed the therapeutic potential of the specific 5-HT6 receptor antagonists 4-amino-N-(2,6-bis-methylamino-pyrimidin-4-yl)-benzenesulfonamide (Ro 04-6790) and 5-chloro-N-(4-methoxy-3-piperazin-1-yl-phenyl)-3-methyl-2-benzothiophenesulfonamide (SB-271046) in rodent models of cognitive function. Although mice express the 5-HT6 receptor and the function of this receptor has been investigated in mice, all reports of activity with 5-HT6 receptor antagonists have used rat models. In the present study, receptor binding revealed that the pharmacological properties of the mouse receptor are different from the rat and human receptor: Ro 04-6790 does not bind to the mouse 5-HT6 receptor, so all in vivo testing included in the present report was conducted in rats. We replicated previous reports that 5-HT6 receptor antagonists produce a stretching syndrome previously shown to be mediated through cholinergic mechanisms, but Ro 04-6790 and SB-271046 failed to attenuate scopolamine-induced deficits in a test of contextual fear conditioning. We also failed to replicate the significant effects reported previously in both an autoshaping task and in a version of the Morris water maze. The results of our experiments are not consistent with previous reports that suggested that 5-HT6 antagonists might have therapeutic potential for cognitive disorders.

Serotonin receptors: their key role in drugs to treat schizophrenia

Serotonin (5-HT)-receptor-based mechanisms have been postulated to play a critical role in the action of the new generation of antipsychotic drugs (APDs) that are usually referred to as atypical APDs because of their ability to achieve an antipsychotic effect with lower rates of extrapyramidal side effects (EPS) compared to first-generation APDs such as haloperidol. Specifically, it has been proposed by Meltzer et al. [J. Pharmacol. Exp. Ther. 251 (1989) 238] that potent 5-HT2A receptor antagonism together with weak dopamine (DA) D2 receptor antagonism are the principal pharmacologic features that differentiate clozapine and other apparent atypical APDs from first-generation typical APD. This hypothesis is consistent with the atypical features of quetiapine, olanzapine, risperidone, and ziprasidone, which are the most common treatments for schizophrenia in the United States and many other countries, as well as a large number of compounds in various stages of development. Subsequent research showed that 5-HT1A agonism may be an important consequence of 5-HT2A antagonism and that substitution of 5-HT1A agonism for 5-HT2A antagonism may also produce an atypical APD drug when coupled with weak D2 antagonism. Aripiprazole, the most recently introduced atypical APD, and a D2 receptor partial agonist, may also owe some of its atypical properties to its net effect of weak D2 antagonism, 5-HT2A antagonism and 5-HT1A agonism [Eur. J. Pharmacol. 441 (2002) 137]. By contrast, the alternative "fast-off" hypothesis of Kapur and Seeman [Am. J. Psychiatry 158 (2001) 360] applies only to clozapine and quetiapine and is inconsistent with the "slow" off rate of most atypical APDs, including olanzapine, risperidone and ziprasidone. 5-HT2A and 5-HT1A receptors located on glutamatergic pyramidal neurons in the cortex and hippocampus, 5-HT2A receptors on the cell bodies of DA neurons in the ventral tegmentum and substantia nigra and GABAergic interneurons in the cortex and hippocampus, and 5-HT1A receptors in the raphe nuclei are likely to be important sites of action of the atypical APDs. At the same time, evidence has accumulated for the important modulatory role of 5-HT2C and 5-HT6 receptors for some of the effects of some of the current APDs. Thus, 5-HT has joined DA as a critical target for developing effective APDs and led to the search for novel drugs with complex pharmacology, ending the exclusive search for single-receptor targets, e.g., the D3 or D4 receptor, and drugs that are selective for them.

5-HT6 receptor binding sites in schizophrenia and following antipsychotic drug administration: autoradiographic studies with [125I]SB-258585

The 5-hydroxytryptamine (5-HT; serotonin)-6 receptor (5-HT6R) is a putative target of atypical antipsychotic drugs and its mRNA expression is altered in schizophrenia. [125I]SB-258585 is a selective 5-HT6R antagonist which has been well characterized for use in the rat brain. The present study evaluated its suitability for receptor autoradiography in the human brain and its application to quantitative studies. The affinity (K(d) approximately 1.2 nM) and relative distribution of binding sites (striatum >> cortex approximately hippocampus) were similar to the rat. The distribution of [125I]SB-258585 binding in these regions was also consistent with that of 5-HT6R mRNA, determined in parallel using in situ hybridization. [125I]SB-258585 binding site densities were measured in dorsolateral prefrontal cortex of 20 patients with chronic schizophrenia and compared with 17 normal subjects. No differences were seen between groups. Neither were [125I]SB-258585 binding site densities affected in the frontal cortex or striatum of rats following 2 weeks' administration of the antipsychotic drugs haloperidol, chlorpromazine, olanzapine, risperidone, or clozapine. In summary, [125I]SB-258585 is a suitable radioligand for studies of human brain 5-HT6R binding sites and shows that their distribution is broadly similar to that of the rodent. The lack of effect of schizophrenia or antipsychotic drug administration on [125I]SB-258585 binding suggests that an altered receptor density does not contribute to any involvement which the 5-HT6R may have in the disease or its treatment.

An RT-PCR study of 5-HT(6) and 5-HT(7) receptor mRNAs in the hippocampal formation and prefrontal cortex in schizophrenia

5-Hydroxytryptamine (5-HT; serotonin) 5-HT(6) receptors (5-HT(6)R) and 5-HT(7) receptors (5-HT(7)R) have been implicated in schizophrenia and as targets of atypical antipsychotic drugs. We have studied the expression of these receptors in the hippocampal formation and dorsolateral prefrontal cortex (DLPFC) of 17 subjects with schizophrenia and 17 controls using reverse transcription-polymerase chain reaction (RT-PCR) with cyclophilin co-amplification. In schizophrenia, 5-HT(6)R mRNA was decreased in the hippocampal formation, and 5-HT(7)R mRNA was decreased in the dorsolateral prefrontal cortex. The mRNAs were unchanged in rats treated for 2 weeks with haloperidol, chlorpromazine, risperidone, olanzapine or clozapine. Regional decreases in 5-HT(6)R and 5-HT(7)R expression in schizophrenia may contribute to the overall serotonergic alterations which occur in the disorder, in part through their interactions with other neurotransmitter systems including glutamate and acetylcholine.

Genetic association analysis of 5-HT(6) receptor gene polymorphism (267C/T) with tardive dyskinesia

Possible involvement of serotonergic (5-hydroxytryptamine: 5-HT) receptors in the pathophysiology of tardive dyskinesia (TD) has been suggested. In the present study, the relationship between the 5-HT(6) receptor gene (HTR6) polymorphisms and TD was studied in 173 Japanese patients with schizophrenia. The 267C/T allele of HTR6 was genotyped using PCR amplification followed by endonuclease digestion. The patients with the three 267C/T genotypes showed no significant difference in gender, age, duration of illness, or current antipsychotic dose. In addition, there were no significant differences in total AIMS scores among patients with the three genotypes. Moreover, no significant differences in genotypes and allele frequencies were observed between subjects with and without TD. These results suggest that the 267C/T polymorphism of HTR6 does not confer increased susceptibility to TD.

Molecular genetics of schizophrenia: past, present and future

Schizophrenia is a severe neuropsychiatric disorder with a polygenic mode of inheritance which is also governed by non-genetic factors. Candidate genes identified on the basis of biochemical and pharmacological evidence are being tested for linkage and association studies. Neurotransmitters, especially dopamine and serotonin have been widely implicated in its etiology. Genome scan of all human chromosomes with closely spaced polymorphic markers is being used for linkage studies. The completion and availability of the first draft of Human Genome Sequence has provided a treasure-trove that can be utilized to gain insight into the so far inaccessible regions of the human genome. Significant technological advances for identification of single nucleo-tide polymorphisms (SNPs) and use of microarrays have further strengthened research methodologies for genetic analysis of complex traits. In this review, we summarize the evolution of schizophrenia genetics from the past to the present, current trends and future direction of research.

Novel polymorphism in the 5'-upstream region of the human 5-HT6 receptor gene and schizophrenia

The localization of 5-hydroxytryptamine6 (5-HT6) receptor in the limbic and cortical regions, and the high affinity of atypical antipsychotic drugs such as clozapine for the receptor, suggest the possible involvement of the receptor in the pathogenesis of schizophrenia. In this study, we searched systematically for polymorphisms in the 5'-upstream region of the human 5-HT6 receptor gene. We identified a trinucleotide repeat polymorphism, (GCC)2/3, at a nucleotide position between -1093 and -1085 bp upstream from the translation start site. Subsequent case-control association study did not demonstrate significant differences of genotype and allele frequency between 206 controls and 246 patients with schizophrenia. Our results suggest that the 5-HT6 receptor gene polymorphism does not confer increased susceptibility to schizophrenia.

Association study of serotonin-6 receptor variant (C267T) with schizophrenia and aggressive behavior

The relative abundance of serotonin type 6 receptors (5-HT6) in some limbic regions and the high affinity of some antipsychotics to 5-HT6 receptors suggest that they might be involved in the pathogenesis of schizophrenic disorders. In a population-based association study, we tested the hypothesis that the allelic variant, C267T, of the human 5-HT6 gene confers susceptibility to schizophrenic disorders and associated aggressive behavior. We genotyped 5-HT6 receptors in 186 patients with schizophrenic disorders and 163 controls. The results demonstrated no significant difference in genotype or allele frequencies between patients with or without aggressive behaviors. However, genotype distribution was significantly different between schizophrenic patients and control subjects. This suggests that the 5-HT6 gene may play a role in the pathogenesis of schizophrenic disorders.