Mapping of the serotonin 5-HT1D alpha autoreceptor gene (HTR1D) on chromosome 1 using a silent polymorphism in the coding region

The effects of a HTR2B stop codon and testosterone on energy metabolism and beta cell function among antisocial Finnish males

Herein, we examined insulin resistance (IR), insulin sensitivity (IS), beta cell activity, and glucose metabolism in subjects with antisocial personality disorder (ASPD), and whether the serotonin 2B (5-HT2B) receptor and testosterone have a role in energy metabolism. A cohort of subjects belonging to a founder population that included 98 ASPD males, aged 25-30, was divided into groups based on the presence of a heterozygous 5-HT2B receptor loss-of-function gene mutation (HTR2B Q20*; n = 9) or not (n = 89). Serum glucose and insulin levels were measured in a 5 h oral glucose tolerance test (75 g) and indices describing IR, IS, and beta cell activity were calculated. Body mass index (BMI) was also determined. Concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid were measured in cerebrospinal fluid, and testosterone levels from serum. An IR-like state comprising high IR, low IS, and high beta cell activity indices was observed among ASPD subjects without the HTR2B Q20* allele. By contrast, being an ASPD HTR2B Q20* carrier appeared to be preventive of these pathophysiologies. The HTR2B Q20* allele and testosterone predicted lower BMI independently, but an interaction between HTR2B Q20* and testosterone lead to increased insulin sensitivity among HTR2B Q20* carriers with low testosterone levels. The HTR2B Q20* allele also predicted reduced beta cell activity and enhanced glucose metabolism. Reduced 5-HT2B receptor function at low or normal testosterone levels may be protective of obesity. Results were observed among Finnish males having an antisocial personality disorder, which limits the generality.

SSRI response in depression may be influenced by SNPs in HTR1B and HTR1A

OBJECTIVES

Desensitization of serotonin 1A (HTR1A) and 1B (HTR1B) autoreceptors has been proposed to be involved in the delayed onset of response to selective serotonin reuptake inhibitors (SSRIs). Variations in gene expression in these genes may thus affect SSRI response.

METHODS

Here, we test this hypothesis in two samples from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D), and show evidence for involvement of several genetic variants alone and in interaction. Initially, three functional single nucleotide polymorphisms (SNPs) in the HTR1B gene and in the HTR1A gene were analyzed in 153 depressed patients treated with citalopram. The 16-item Quick Inventory of Depressive Symptomatology Clinician scores were evaluated over time with respect to genetic variation.

RESULTS

Individuals homozygous for the -1019 G allele (rs6295) in HTR1A showed the higher baseline 16-item Quick Inventory of Depressive Symptomatology Clinician scores (P=0.033), and by 12 weeks had a significantly lower response rate (P=0.005). HTR1B haplotypes were estimated according to the previously reported in-vitro expression levels. Individuals who were homozygous for the high-expression haplotype showed significantly slower response to citalopram (P=0.034). We then analyzed more SNPs in the extended overall STAR*D sample. Although we could not directly test the same functional SNPs, we found that homozygotes for the G allele at rs1364043 in HTR1A (P=0.045) and the C allele of rs6298 in HTR1B showed better response to citalopram over time (P=0.022). Test for interaction between rs6298 in HTR1B and rs1364043 in HTR1A was significant (overall P=0.032).

CONCLUSION

Our data suggest that an enhanced capacity of HTR1B or HTR1A transcriptional activity may impair desensitization of the autoreceptors during SSRI treatment.

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.

Serotonin in alcoholic violent offenders

Finnish alcoholic, impulsive, habitually violent offenders have been found to have low brain serotonin (5-hydroxytryptamine; 5-HT) turnover which is associated with impaired impulse control, a history of suicide attempts, hypoglycaemic tendency after an oral glucose load and diurnal activity rhythm dysregulation or hyperactivity. Relatively high cerebrospinal fluid (CSF) free testosterone concentration is a further characteristic of the offenders with antisocial personality disorder. The impulsive offenders may represent a behaviourally extreme group of type 2 alcoholics as defined by Cloninger. A large cohort of 800 subjects, including alcoholic violent offenders, their relatives and male controls, has now been gathered from Finland with support from the National Institute on Alcohol Abuse and Alcoholism. About 200 subjects have provided CSF samples. Leukocytes from the whole cohort have been harvested and immortalized. Genes regulating 5-HT functions are now being systematically analysed from these samples. Thus far, polymorphisms of the tryptophan hydroxylase (TPH) and 5-HT2C receptor genes have been the most informative findings.

The serotonin 5-HT1D receptor gene and attention-deficit hyperactivity disorder in Chinese Han subjects

Attention-deficit/hyperactivity disorder (ADHD) is a heritable disease. Serotonin is one of the neurotransmitters involved in the etiology of ADHD. Serotonin-1D receptors are autoreceptors which can regulate the release of serotonin in brain, so the HTR1D gene may be predisposing. The current study genotyped two variants of HTR1D gene in 272 ADHD trios of Chinese ethnicity, that is 1350T > C in the coding region and 1236A > G in 3'-UTR by the use of transmission disequilibrium test (TDT). The A allele of the 1236A > G polymorphism exhibited both a trend toward preferential transmission to ADHD probands (chi2 = 3.815, P = 0.051) and a significant preferential transmission to probands of ADHDC (chi2 = 4.198, P = 0.040). Additional polymorphisms in this gene need to be studied further.

Lack of association or linkage disequilibrium between schizophrenia and polymorphisms in the 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes: family-based association study

Genetic factors play a major role in the etiology of schizophrenia and disturbances of serotonergic pathways have been implicated in this disorder. The aim of the present study was to examine genetic association between schizophrenia and polymorphisms in the 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) autoreceptor genes in ninety trios from Portugal. No association or linkage disequilibrium was obtained between schizophrenia and 5-HT1Dalpha and 5-HT1Dbeta autoreceptor genes with both haplotype relative risk (HRR) and transmission disequilibrium test (TDT). Concerning 5-HT1Dbeta autoreceptor gene, also negative results was obtained in the analysis of the haplotypes with transmit. Thus, our data provide no support for the hypothesis that polymorphisms at 5-HT1Dalpha (TaqI) and 5-HT1Dbeta (T261G and G861C) genes contributes to susceptibility to schizophrenia in the Portuguese population.

Nonparametric linkage analysis between schizophrenia and candidate genes of dopaminergic and serotonergic systems

BACKGROUND

Alterations in dopaminergic and serotonergic systems have been implicated in the pathophysiology of schizophrenia for many years. This study was performed to assess the possible involvement of the dopamine receptor genes D2 (DRD2), D3, D4, serotonin receptor genes 1Da, 1Db, and 2A in the etiology of schizophrenia.

METHODS

We examined 33 multiplex schizophrenic families from Portugal.

RESULTS

Linkage analysis performed by GENEHUNTER showed nonsignificant linkage for these genes. A maximum nonparametric linkage score of 1.635 (P=.032) at DRD2 gene was observed, and this finding suggests DRD2 gene for further studies.

CONCLUSION

the polymorphisms studied at dopamine receptor genes D3, D4, serotonin receptor genes 1Da, 1Db, and 2A do not have a major effect in susceptibility to schizophrenia in a Portuguese population.

Suicide and serotonin: study of variation at seven serotonin receptor genes in suicide completers

Suicide is an important public health problem, accounting for a significant proportion of total mortality among young people, particularly males. There is growing and consistent evidence suggesting that genetic factors play an important role in the predisposition to suicide. Based on several lines of evidence supporting a reduced serotonergic neurotransmission in subjects who committed suicide, we investigated variation at genes that code for serotonin receptor 1B (5-HTR1B), 1Dalpha (5-HTR1Dalpha), 1E (5-HTR1E), 1F (5-HTR1F), 2C (5-HTR2C), 5A (5-HTR5A), and 6 (5-HTR6) in a total sample of 106 suicide completers and 120 normal controls. No differences were observed in allelic or genotypic distributions between groups for any of the loci investigated. Moreover, further analysis according to suicide method or psychopathology also failed to reveal differences between groups. Our results do not support a substantial role of these serotonergic receptors in suicide completion.

Schizophrenia spectrum disorders: an autosomal-wide scan in multiplex pedigrees

Genome-wide linkage studies, examining the relationship between the schizophrenia syndrome(s) and possible susceptibility regions within the human genome have identified multiple regions within which linkage to the syndrome may be explored. No regions have been found to provide supportive evidence for linkage in all cohorts. These findings are consistent with the schizophrenia syndrome being genetically heterogeneous, with genetic susceptibility arising from multiple sites which are differentially distributed in from pedigree to pedigree. The authors present data from an autosomal-wide scan of 30 multiplex pedigrees, each with a mean of 4.1 members affected with a schizophrenia spectrum disorder with respect to regions of interest for linkage with the schizophrenia spectrum disease(s). Partial, though not significant replications of susceptibility sites at D1S518 (P=0.029) described by Shaw et al. (1998: Shaw, S.H., Kelly, M., Smith, A.B., Shields, G., Hopkins, P.J., Loftus, J., Laval, S.H., Vita, A., DeHert, M., Cardon, L.R., Crow, T.J., Sherrington, R., DeLisi, L.E., 1998. A Genome-wide search for schizophrenia susceptibility genes. Am. J. Med. Genet. (Neuropsychiatric Genet.) 81, 364-376.), and at D5S426 (P=0.015) described by : Silverman, J.M., Greenberg, D.A., Altstiel, L.D., Siever, L.J., Mohs, R.C., Smith, C.J., Zhou, G., Hollander, T.Y., Yang, X.-P., Kedache, M., Li, G., Zaccario, M.L., Davis, K.L., 1996. Evidence of a locus for schizophrenia and related disorders on the short arm of chromosome 5 in a large pedigree. Am. J. Med. Genet. 67, 162-171.) were documented using multipoint non-parametric (NPL) statistics. Two additional novel regions worthy of further investigation were identified at D1S1150 (P=0.004) and at D20S171 (P=0.009). Previously reported genomic regions of interest for the schizophrenias are reviewed in the context of the same/flanking markers utilized with the present cohort of pedigrees. The data further suggests that only a fraction of pedigrees multiplex for schizophrenia link at any single susceptibility region.

Pharmacogenomics and schizophrenia

Although antipsychotic drugs are effective in alleviating schizophrenic symptoms, individual differences in patient response suggest that genetic components play a major role, and pharmacogenetic studies have indicated the possibility for a more individually based pharmacotherapy. The new field of pharmacogenomics, which focuses on genetic determinants of drug response at the level of the entire human genome, is important for development and prescription of safer and more effective individually tailored drugs. DNA microarray (DNA chip) analysis enables genome-wide scanning, using the high-density single nucleotide polymorphisms map. Pharmacogenomics will aid in understanding how genetics influence disease development and drug response, and contribute to discovery of new treatments. The rate of discovery of those polymorphisms will depend on the quality of the drug response phenotype. Prospective genotyping of schizophrenic patients for the many genes at the level of the drug target, drug metabolism, and disease pathways will contribute to individualized therapy matching the patient's unique genetic make-up with an optimally effective drug.

Comparison of the role of dopamine, serotonin, and noradrenaline genes in ADHD, ODD and conduct disorder: multivariate regression analysis of 20 genes

The present study is based on the proposal that complex disorders resulting from the effects of multiple genes are best investigated by simultaneously examining multiple candidate genes in the same group of subjects. We have examined the effect of 20 genes for dopamine, serotonin, and noradrenergic metabolism on a quantitative score for attention deficit hyperactivity disorder (ADHD) in 336 unrelated Caucasian subjects. The genotypes of each gene were assigned a score from 0 to 2, based on results from the literature or studies in an independent set of subjects (literature-based scoring), or results based on analysis of variance for the sample (optimized gene scoring). Multivariate linear regression analysis with backward elimination was used to determine which genes contributed most to the phenotype for both coding methods. For optimized gene scoring, three dopamine genes contributed to 2.3% of the variance, p = 0.052; three serotonin genes contributed to 3%, p = 0.015; and six adrenergic genes contributed to 6.9%, p = 0.0006. For all genes combined, 12 genes contributed to 11.6% of the variance, p = 0.0001. These results indicate that the adrenergic genes play a greater role in ADHD than either the dopaminergic or serotonergic genes combined. The results using literature-based gene scoring were similar. An examination of two additional comorbid phenotypes, conduct disorder and oppositional defiant disorder (ODD), indicated they shared genes with ADHD. For ODD different genotypes of the same genes were often used. These results support the value of the simultaneous examination of multiple candidate genes.

Unified approach to the analysis of genetic variation in serotonergic pathways

Serotonin is a key neurotransmitter in the central nervous system, and dysregulation of serotonergic pathways has been implicated in the pathogenesis of many complex psychiatric diseases. Polymorphisms of many of the genes involved in serotonin biosynthesis, catabolism, and response have been reported, suggesting that genetic variability may underlie the development of diseases such as schizophrenia, obsessive compulsive disorder, and suicide. A number of single-gene polymorphisms in serotonergic pathways have been examined in these and other diseases, but to date results from this candidate gene approach have been disappointing. Although this may be because the detection of a small effect may require the analysis of large numbers of patients and controls, an alternative explanation is that the clinical importance of a single subtle genetic variant may be overlooked unless other functionally related genes are studied in tandem. To facilitate an integrated analysis, we have developed a PCR-SSP-based assay that permits the simultaneous genotyping of 13 single nucleotide polymorphisms in 9 serotonergic genes under identical conditions. These genes include tryptophan hydroxylase, tryptophan dioxygenase, monoamine oxidase A, and the serotonin receptors 5HT1A, 5HT1D-alpha, 5HT1D-beta, 5HT2A, 5HT2C, and 5HT5A. Using this technology, we have genotyped 100 Caucasoid control individuals and demonstrate that this approach is reliable, quick, cheap, and easy to interpret. We anticipate that this will facilitate the analysis of the genetic basis of susceptibility and phenotypic variability of a number of complex psychiatric diseases. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 88:621-627, 1999.

Genetic factors in anorexia nervosa

Anorexia nervosa is a severe and complex disorder with incompletely known vulnerability factors. It is generally recognized that anorexia nervosa is a familial disorder, but the majority of twin studies have shown that the concordance rate for monozygotic twins is higher (on average 44%) than for dizygotic twins (on average 12.5%). This difference in concordance rates shows that genetic factors, more than common familial environment, may explain why the 'anorexia nervosa' phenotype runs in families. In order to estimate the heritability in the broad sense of anorexia nervosa according to published familial and twin studies, we first assessed the intrapair correlation between monozygotic and dizygotic twins, and secondly calculated the deviation threshold of relatives of affected probands from the relative mean. In this review, we obtained an estimation of the heritability at 0.72 according to all published controlled familial studies (six references quoted in MEDLINE(R)), and 0.71 for all published twin studies (59 references quoted in MEDLINE(R)). This estimation is close to the ones previously proposed, between 0. 5 and 0.8. Familial and twin studies may also help to define the boundaries of the phenotype, shedding light on the complex relationship between anorexia nervosa on the one hand, and bulimia nervosa, mood disorders, and alcoholism on the other. Demonstrating the importance of genetic factors in anorexia nervosa, and more specifically for anorexia of the restrictive type, requires not only prospective and adoption studies (which are still lacking), but also genetic polymorphisms analyses, which began very recently.

Serotonergic basis of antipsychotic drug effects in schizophrenia

Recent attention has been focused on the involvement of serotonin (5-HT) in the pathophysiology of schizophrenia and its role in mediating antipsychotic drug effects. There are two reasons for the new emphasis: the tremendous success of the so-called "atypical" antipsychotic drugs (a common feature of which is their high affinity for specific 5-HT receptor subtypes); and the elucidation of a complex family of 5-HT receptors whose function and pharmacology is only beginning to be understood. This paper will review the evidence that pertains to the role of 5-HT in mediating antipsychotic drug effects. The interaction of dopamine and 5-HT systems will be reviewed, and the mechanisms of action of atypical antipsychotic drugs will be evaluated in this context. The impact of serotonin on neurodevelopment, and the involvement of serotonin in the psychotomimetic and psychotogenic properties of hallucinogens, will be discussed. Together, these facts will be placed into the context of changes in serotonergic function in schizophrenia.

Assignment of the human serotonin 4 receptor gene (HTR4) to the long arm of chromosome 5 (5q31-q33)

In the present study, we report the chromosomal localization of the human 5-HT4 receptor gene (HTR4) by the analysis of somatic cell hybrids. Based upon genomic sequences of the HTR4 gene, a primer set was selected that reacted with human genomic DNA but not mouse or hamster genomic DNA. Using monochromosomal hybrid cell lines of the NIGMS Mapping Panel 2 we localized the HTR4 gene to human chromosome 5. To confirm the localization on chromosome 5 and to further sublocalize the HTR4 gene, the radiation hybrid panel RH3 was similarly analysed. Significant linkage was obtained to genetic marker D5S2654. This localizes the HTR4 gene to human chromosome 5q31-q33.

Assignment of the human serotonin 1F receptor gene (HTR1F) to the short arm of chromosome 3 (3p13-p14.1)

In the present study, we report the chromosomal localization of the human 5-HT1F receptor gene (HTR1F) by the analysis of somatic cell hybrids. Based upon the HTR1F cDNA sequence, a primer set that reacted with human genomic DNA but not mouse or hamster genomic DNA was derived from the relatively nonconserved 5'-untranslated and coding region. Using monochromosomal hybrid cell lines of the NIGMS Mapping Panel 2 we localized the HTR1F to human chromosome 3. To confirm the localization on chromosome 3 and to further sublocalize the HTR1F gene, a set of human cell hybrids regionally separating chromosome 3 into 7 regions was similarly analysed. Analysis of this regional panel showed that the HTR1F gene was located proximal to the 3p14.1 breakpoint in hybrid APH14 and distal to the breakpoint in 3p13 in hybrid APH13. This localizes the HTR1F gene to human chromosome 3p13-p14.1.

Sequence, splice site and population frequency distribution analyses of the polymorphic human tryptophan hydroxylase intron 7

A human tryptophan hydroxylase intron seven polymorphism previously associated with low CSF 5-HIAA and suicidal behavior was sequenced and characterized for its potential role in TPH pre-mRNA splicing. Two polymorphic sites were identified: A218C and A779C. The 779A allelic frequency in various populations ranged from 0.43 to 0.61 and was in strong linkage disequilibrium with the A218C site. A218C provides a site for restriction fragment length polymorphism analysis. TPH mRNA was reverse-transcribed and sequenced. No aberrant splice products from the 779A or 779G TPH genes were detected nor were any other polymorphic nucleotides found.

Serotonin in early-onset alcoholism

This chapter examines current, common schemes to subgroup alcoholics to arrive at relatively homogeneous groups of patients to facilitate psychobiological and molecular genetic studies. Early-onset, male-limited alcoholism is commonly associated with antisocial personality disorder or antisocial behavioral traits. It is often preceded by early-onset aggressiveness, which is followed by conduct disorder. Early-onset alcoholism among men is associated with low central serotonin turnover rate. The data concerning platelet MAO activity and serotonin uptake to platelets among early-onset alcoholics are conflicting. Recent molecular genetic and brain imaging studies on early-onset alcoholics are preliminary but appear very promising.

Identifying alcoholism vulnerability alleles

Identification of vulnerability alleles is one starting point for elucidating the web of interactions leading to alcoholism so that treatment and prevention can be improved. Heritability studies indicate that vulnerability alleles exist. Two molecular approaches for identifying them, direct analysis of candidate genes and genetic linkage, are highlighted in this review. Methodological problems that have been partially addressed and limitations for the applicability of the genetic findings are discussed.