DNA variation and psychopharmacology of the human serotonin receptor 1B (HTR1B) gene

Combined HTR1A/1B methylation and human functional connectome to recognize patients with MDD

OBJECTIVES

This study aimed to use a machine-learning method to identify HTR1A/1B methylation and resting-state functional connectivity (rsFC) related to the diagnosis of MDD, then try to build classification models for MDD diagnosis based on the identified features.

METHODS

Peripheral blood samples were collected from all recruited participants, and part of the participants underwent the resting-state fMRI scan. Features including HTR1A/1B methylation and rsFC were calculated. Then, the initial feature sets of epigenetics and neuroimaging were separately input into an all-relevant feature selection to generate significant discriminative power for MDD diagnosis. Random forest classifiers were constructed and evaluated based on identified features. In addition, the SHapley Additive exPlanations (SHAP) method was adapted to interpret the diagnostic model.

RESULTS

A combination of selected HTR1A/1B methylation and rsFC feature sets achieved better performance than using either one alone - a distinction between MDD and healthy control groups was achieved at 81.78% classification accuracy and 0.8948 AUC.

CONCLUSION

A high classification accuracy can be achieved by combining multidimensional information from epigenetics and cerebral radiomic features in MDD. Our approach can be helpful for accurate clinical diagnosis of MDD and further exploring the pathogenesis of MDD.

Animal Models for OCD Research

OCD has lagged behind other psychiatric illnesses in the identification of molecular treatment targets, due in part to a lack of significant findings in genome-wide association studies. However, while progress in this area is being made, OCD's symptoms of obsessions, compulsions, and anxiety can be deconstructed into distinct neural functions that can be dissected in animal models. Studies in rodents and non-human primates have highlighted the importance of cortico-basal ganglia-thalamic circuits in OCD pathophysiology, and emerging studies in human post-mortem brain tissue point to glutamatergic synapse abnormalities as a potential cellular substrate for observed dysfunctional behaviors. In addition, accumulated evidence points to a potential role for neuromodulators including serotonin and dopamine in both OCD pathology and treatment. Here, we review current efforts to use animal models for the identification of molecules, cell types, and circuits relevant to OCD pathophysiology. We start by describing features of OCD that can be modeled in animals, including circuit abnormalities and genetic findings. We then review different strategies that have been used to study OCD using animal model systems, including transgenic models, circuit manipulations, and dissection of OCD-relevant neural constructs. Finally, we discuss how these findings may ultimately help to develop new treatment strategies for OCD and other related disorders.

Adenylyl cyclase 7 and neuropsychiatric disorders: A new target for depression?

Adenylyl cyclases (ACs) are enzymes that catalyze the production of cyclic adenosine monophosphate (cAMP) from adenosine triphosphate (ATP). Humans express nine isoforms of membranous ACs and a soluble AC. Studies with genetic knockout or overexpression rodent models have indicated that AC isoforms may be targeted to achieve specific therapeutic outcomes. AC1, for instance, has been suggested and pursued as a target for relieving pain. Notably, previous studies examining genetically modified mice as well as human genetic polymorphisms have suggested a link between AC7 activity and depressive disorders. In the present review we present an overview on AC function and discuss the most recent developments to target AC isoforms for drug therapies. We next focus on discussing the available literature on the molecular and animal pharmacology of AC7 highlighting the available studies on the role of AC7 in depressive disorders. In addition, we discuss other possible physiological functions of AC7 relating to ethanol effects and the immune system and conclude with considerations about pharmacological modulation of AC7.

Epigenetic and genetic variants in the HTR1B gene and clinical improvement in children and adolescents treated with fluoxetine

The serotonin 1B receptor (5-HT_1B) is important to both the pathogenesis of major depressive disorder and the antidepressant effects of selective serotonin reuptake inhibitors. Although fluoxetine has been shown to be effective and safe in children and adolescents, not all patients experience a proper clinical response, which has led to further study into the main factors involved in this inter-individual variability. Our aim was to study the effect of epigenetic and genetic factors that could affect 5-hydroxytryptamine receptor 1B (HTR1B) gene expression, and thereby response to fluoxetine. A total of 83 children and adolescents were clinically assessed 12weeks after of initiating an antidepressant treatment with fluoxetine for the first time. We evaluated the influence of single nucleotide polymorphisms (SNPs) specifically located in transcription factor binding sites (TFBSs) on their clinical improvement. A combined genetic analysis considering the significant SNPs together with the functional variant rs130058 previously associated in our population was also performed. Moreover, we assessed, for the first time in the literature, whether methylation levels of the HTR1B promoter region could be associated with the pharmacological response. Two, rs9361233 and rs9361235, were significantly associated with clinical improvement after treatment with fluoxetine. The heterozygous genotype combination analysis showed a negative correlation with clinical improvement. The lowest improvement was experienced by patients who were heterozygous for all three SNPs. Moreover, a negative correlation was found between clinical improvement and the average methylation level of the HTR1B promoter. These results give new evidence for the role of epigenetic and genetic factors which could modulate HTR1B expression in the pharmacological response to antidepressants.

Genetics of obsessive–compulsive disorder: a research update

The genetic study of obsessive-compulsive disorder (OCD) has made significant gains in the past decade. However, etiological gene findings are still elusive. Epidemiological studies, including family and twin studies, strongly support a genetic component for OCD. In addition, complex segregation analyses suggest the presence of at least one major gene. The neurobiology of OCD also lends support to the notion that programmed CNS-based biological processes underlie OCD symptom expression, with mapping of brain circuits to fronto-subcortical circuits in a consistent manner. Genetic linkage studies of OCD, using families with multiple affected relatives, have generated several suggestive linkage peaks, regions that may harbor a gene or genes for OCD. However, the presence of multiple linkage peaks has added to the complexity of OCD genetics, suggesting that the exploration of gene-gene interactions and gene-environment interactions, in addition to the exploration of alternate phenotypes based on symptom expression, age at onset or comorbid conditions, may be key in locating etiologic genes. Finally, candidate gene studies, while promising, are not yet associated with linkage regions, except in the case of the glutamate transporter gene SLC1A1 in 9p24. While OCD appears to have a genetic component, additional innovative research is needed to unravel the genetic influences in the disorder.

Genetic association of 5-HT1A and 5-HT1B gene polymorphisms with migraine in a Turkish population

Migraine, a very common headache disorder, is regarded as a polygenic disease and serotonergic pathways appear to play a major role in its pathogenesis. The present study was designed to explore the associations of polymorphisms of 5-hydroxytryptamine (serotonin) receptor 1A (5-HT1A) and 5-hydroxytryptamine receptor 1B (5-HT1B) genes in Turkish migraine patients. 5-HT1A C-1019G (rs6295) promoter and 5-HT1B G861C (rs6296) exon polymorphisms in 203 migraine patients and 202 healthy subjects were analyzed by using polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis. Allele and genotype frequencies were not significantly different between migraine patients and healthy subjects for both the 5-HT1A C-1019G promoter and 5-HT1B G861C exon polymorphisms. Our data do not support the hypothesis that 5-HT1A C-1019G and 5-HT1B G861C polymorphisms have effects on migraine.

The role of the serotonergic system in suicidal behavior

Serotonin is a widely investigated neurotransmitter in several psychopathologies, including suicidal behavior (SB); however, its role extends to several physiological functions involving the nervous system, as well as the gastrointestinal and cardiovascular systems. This review summarizes recent research into ten serotonergic genes related to SB. These genes - TPH1, TPH2, SLC6A4, SLC18A2, HTR1A, HTR1B, HTR2A, DDC, MAOA, and MAOB - encode proteins that are vital to serotonergic function: tryptophan hydroxylase; the serotonin transporter 5-HTT; the vesicular transporter VMAT2; the HTR1A, HTR1B, and HTR2A receptors; the L-amino acid decarboxylase; and the monoamine oxidases. This review employed a systematic search strategy and a narrative research methodology to disseminate the current literature investigating the link between SB and serotonin.

Serotonin receptor 1B genotype and hostility, anger and aggressive behavior through the lifespan: the Young Finns study

The serotonin system has been shown to be involved in the regulation of hostility, anger, and aggressive behavior. Previous molecular genetic studies suggest that the serotonin receptor 1B (HTR1B) rs6296 genotype might have a particular role in these types of behaviors. We examined whether HTR1B is related to hostility, anger, and aggressive behavior phenotypes over a lifespan and whether it modifies the connection between childhood aggressive behavior and adulthood hostility and anger. The participants were 967 women and men from a large population based sample (The Young Finns Study) with a 27-year follow-up. Childhood aggressive behavior was reported by the mother twice when the participants were 3 to 12 years of age. Adulthood hostility and anger were self-reported by the participants between ages 24 and 36. Childhood aggressive behavior predicted adulthood hostility over 27 years. HTR1B SNP rs6296 was associated with childhood aggressive behavior but not with adulthood anger or hostility. The HTR1B SNP rs6296 modified the association between childhood aggressive behavior and adulthood hostility. Aggressive behavior and hostility might form a life course pattern, and the HTR1B might contribute to a development of this pattern.

Peter Riederer "70th birthday" neurobiological foundations of modern addiction treatment

Alcohol dependence is caused by complex interactions of multiple susceptibility genes with little effect each and environmental factors. Candidate genes influence metabolism of alcohol, such as alcohol dehydrogenase and aldehyde dehydrogenase, and modulatory transmitter systems, such as the dopaminergic, serotonergic, acetylcholinergic, gamma-aminobutyric acidergic, and various neuropeptidergic systems. Dysfunctional behavioral choices, learning, and memory are involved in the etiology of alcohol dependence. Systematic promotion and maintenance of motivation is a lifetime challenge in the treatment of alcohol use disorders. The second step of treatment management is the discontinuation of alcohol consumption. Withdrawal symptoms can be treated with gamma-aminobutyric acidergic substances such as benzodiazepines. Long-term relapse prevention is another challenge. Multimodal treatment can include naltrexone, a non-selective opioid receptor antagonist, or acamprosate, an N-methyl-D-aspartate receptor modulator, which are first line for pharmacological treatment on the basis of recent Cochrane analyses. Due to the complexity of etiology with both psychological and neurobiological factors, future treatment management of alcoholism may include the combination of individualized disorder-specific psychotherapy and drugs acting on different neuronal pathways, on the basis of individual vulnerability. However, the question remains unsolved whether an individualized approach is feasible and how subgroups should be defined.

Polymorphisms of the serotonin transporter and receptor genes: susceptibility to substance abuse

Serotonin (5-hydroxytryptamine [5-HT]) is an important neurotransmitter implicated in regulating substance-use disorder (SUD) acquisition, maintenance, and recovery. During the past several years, an abundance of research has begun discovering and describing specific 5-HT genetic polymorphisms associated with SUDs. Genetic variations in the 5-HT system, such as SLC6A4, HTR1B, HTR2A, HTR2C, HTR3 (HTR3A, HTR3B, HTR3C, HTR3D, and HTR3E), likely play a role contributing to SUD patient heterogeneity. The 5-HT transporter-linked polymorphic region S allele, located in SLC6A4, has now been modestly associated with alcohol dependence in two large meta-analyses. Additional 5-HT genes may also play a role but have not been extensively investigated. A limited number of SUD treatment studies have included 5-HT gene variation as moderating treatment outcomes, but the results have been equivocal. Future research on 5-HT addiction genetics should adopt whole-genome sequencing technology, utilize large study samples, and collect data from multiple ethnic groups. Together, these methods will build on the work already conducted with the aim of utilizing 5-HT genetics in SUD treatment settings.

A haplotype analysis is consistent with the role of functional HTR1B variants in alcohol dependence

BACKGROUND

Animal and human studies have suggested that the serotonergic system plays an important role in alcohol consumption and abuse, mainly due to the serotonin receptor 1B (5-HT(1B)) function in the mesolimbic reward pathway. Association studies between the HTR1B gene variants and alcoholism have found significant results. There is also evidence for a complex balancing regulation of the gene by two functional variants in the promoter region (rs11568817 and rs130058), which are in linkage disequilibrium.

METHODS

The aim of this study is to investigate the role of the most relevant variants (rs11568817, rs130058, rs6296 and rs13212041) of the HTR1B gene in the susceptibility to alcohol dependence. The sample comprised 136 Brazilian alcoholics of European descendent and 237 controls.

RESULTS

The results suggest an association between a functional variant of the gene (rs11568817) and alcohol dependence (p=0.001). In addition, this association could also be confirmed in an independent sample using imputed data from a GWAS, where marginal significant association (p=0.03, one-tailed) with the same allele was obtained. The pattern of distribution of haplotypes was significantly different between patients and controls (p<0.0001), which is consistent with the role of the two functional variants of the promoter region.

CONCLUSION

In conclusion, our findings point to an association between functional variants in the promoter region of the HTR1B gene and alcohol dependence, supporting previous neurobiological evidences of the involvement of HTR1B variations in alcohol-related phenotypes.

Polymorphism G861C of 5-HT receptor subtype 1B is associated with heroin dependence in Han Chinese

The serotoninergic (5-HT) system regulates neuronal activity in broad brain regions, and appears to be particularly important for modulating behavioral and physiological functions such as mood, emotion, sleep and appetite. Central 5-HT deregulation may be involved in many neuropsychological disorders, which include substance abuse and addiction. Previous studies suggest that genetic polymorphisms in some 5-HT receptor genes may relate to heroin dependency. Here we examined potential association between heroin dependence and four single nucleotide polymorphisms (SNPs) of 5-HT receptors (A-1438G and T102C of HTR(2A), and G861C and A1180G of HTR(1B)) in a cohort of Han Chinese. Participants included 303 heroin-dependent subjects who were recruited into the Methadone Maintenance Treatment (MMT) Program in the Xi'an Mental Health Center, and 300 healthy controls. The resulting data yielded a significantly higher frequency of the HTR(1B) G allele with G861C among the heroin-dependent subjects relative to controls (p=0.001 after Bonferroni correction). Further genotype and clinical phenotype correlation study of the G861C carriers showed that the amount of heroin self-injection was higher in patients with the GG genotype relative to CC and CG genotypes (p<0.01). These findings point to a role for HTR(1B) polymorphism in heroin dependence among Han Chinese, and may be informative for future genetic or neurobiological studies on heroin dependence.

Genetics of alcohol dependence

Twin, family, and adoption studies have consistently shown that genetic factors play an important role in the pathogenesis of alcohol dependence. Numerous studies have aimed to identify genes that contribute to susceptibility to alcohol dependence. Whole-genome linkage studies have identified several chromosomal regions that are linked with alcohol dependence. Association studies have also identified genes associated with alcohol dependence. Alcohol-metabolizing enzymes, such as alcohol dehydrogenase-1B and aldehyde dehydrogenase-2, are the most well-established genes that have polymorphisms associated with the risk for alcohol dependence. Polymorphisms in gamma-aminobutyric acid receptor genes are also reported to be associated with alcohol dependence. The polymorphism of opioid receptor mu 1 gene is of interest because it alters the treatment effects of naltrexone. Several genes related to neural transmission have been reported to be associated with alcohol dependence, but results are inconsistent among studies. One reason for these inconsistent results is the great heterogeneity of alcohol dependence. Classifying alcohol dependence into homogeneous phenotypes is a good strategy to solve this problem. Recently, several genome-wide association studies have been reported. Genome-wide association studies enable hypothesis-free genome mapping of vulnerability-contributing genes and are expected to add data to identify genes associated with the susceptibility to alcohol dependence. Knowledge of the genetic basis of alcohol dependence is growing and leads to a better understanding of the biological mechanisms of addiction, which can help with strategies to prevent and treat this disease.

Association between the 5-HTR1B gene polymorphisms and alcohol dependence in a Han Chinese population

The human serotonin receptor 1B (HRT1B) plays an important role in regulating serotonin release. Previous research has suggested that the genetic variation of the HTR1B gene may confer susceptibility to alcoholism or some subtypes of alcohol dependence, but the evidence has been inconsistent. The aim of the present study is to examine whether polymorphic variants of the HTR1B gene are associated with alcohol dependence subtypes or drinking-related behaviors in Chinese Han population. Alcohol-dependent (AD) male patients (n=135) and controls (n=143) were genotyped for two polymorphisms: A161T in the promoter region and the synonymous variation G861C in the coding region of HTR1B. The results showed that the A161T polymorphism was associated with alcohol dependence (T vs. A allele: p=0.002; OR=2.18, 95% CI: 1.32-3.60). This association was strengthened in those with positive family history (OR=3.12, 95% CI: 1.71-5.70) and/or early onset (OR=4.53, 95% CI: 2.18-9.44) of alcohol dependence. The A161T variant was also significantly associated with age of onset of alcoholism (p=0.001). Furthermore, there was a significant difference of haplotypic frequencies between patients and controls (χ(2)=14.84, df=3, p=0.002), with one common haplotype AG of being significantly underrepresented among the patient group compared to the control group (34% vs. 47.7%, permutation p=0.0034; OR=0.56; 95% CI: 0.39-0.79). These findings confirm HTR1B as a susceptibility gene for alcohol dependence in the sample of Chinese Han population. The HTR1B A-161T polymorphism may be particularly valuable as a functional genetic marker for alcoholism and merits additional study.

Association analysis of serotonin receptor 1B (HTR1B) and brain-derived neurotrophic factor gene polymorphisms in Borderline personality disorder

The purpose of this study was to test for association between Borderline personality disorder (BPD) and variants of the HTR1B and the brain-derived neurotrophic factor (BDNF) gene. We genotyped four HTR1B and the functional BDNF G196A marker in 161 Caucasian BPD patients and 156 healthy controls. There were no significant differences between groups in genotype or haplotype distribution of HTR1B markers or in genotype distribution of the BDNF marker. Logistic regression analyses revealed an over-representation of the BDNF 196A allele in HTR1B A-161 allele carrying BPD patients.

The genetics of obsessive-compulsive disorder and Tourette's syndrome: what are the common factors?

Genetic discovery in obsessive-compulsive disorder and Tourette's syndrome has made significant progress in the past decade. The two disorders are phenomenologically, epidemiologically, and probably pathophysiologically related; however, as with most neuropsychiatric disorders, gene discovery has been challenging. Genetic epidemiology studies support the existence of susceptibility genes in both disorders, and more extensive genome-wide studies are under way. Gene pathways involving neurotransmitter (serotonin, dopamine, glutamate) and neurodevelopment (synaptic, homeobox) domains have been examined, but more complex genetic mechanisms remain largely unexplored. This review addresses the current state of genetic research in obsessive-compulsive disorder and Tourette's syndrome, emphasizing commonalities between the disorders. Questions on common genetic substrates, the use of endophenotypes, and the utility of genetic data to inform pharmacologic treatment are also addressed.

Chronic reductions in serotonin transporter function prevent 5-HT1B-induced behavioral effects in mice

BACKGROUND

Obsessive-compulsive disorder (OCD) is characterized by intrusive thoughts, images, or impulses and/or repetitive stereotypical behavior. Obsessive-compulsive disorder patients exhibit reduced prepulse inhibition (PPI) and symptom exacerbation after challenge with 5-HT1B receptor agonists. Recently, gain-of-function alleles of the serotonin transporter (5-HTT) have been associated with OCD. We tested the hypothesis that reducing 5-HTT function chronically, either genetically or via serotonin reuptake inhibitor (SRI) treatment, attenuates PPI deficits and perseverative hyperlocomotion induced by 5-HT1B agonists in mice.

METHODS

Mice received subchronic or chronic pretreatment with the SRI fluoxetine and acute treatment with RU24969 (5-HT1A/1B agonist) or 8-OH-DPAT (5-HT1A agonist) and were assessed for PPI, locomotor activity, and spatial patterns of locomotion. The same measures were evaluated in 5-HTT wild-type (WT), heterozygous (HT), and knockout (KO) mice after RU24969 treatment. The effects of WAY100635 (5-HTA antagonist) or GR127935 (5-HT1B/D antagonist) pretreatment on RU24969-induced effects were evaluated. Finally, 5-HT1B binding and functional coupling were assessed in 5-HTT-WT, -HT, and -KO mice, and normal fluoxetine-treated mice.

RESULTS

Chronic, but not subchronic, fluoxetine treatment prevented RU24969-induced PPI deficits and perseverative hyperlocomotion. These RU24969-induced effects were mediated via 5-HT1B and not 5-HT1A receptors. 5-HTT-KO mice showed no effects of RU24969, and 5-HTT-HT mice exhibited intermediate phenotypes. 5-HT1B binding and functional coupling were reduced in the globus pallidus and substantia nigra of 5-HTT-KO mice.

CONCLUSIONS

Our results demonstrate that chronic, but not subchronic, fluoxetine treatment and 5-HTT knockout robustly attenuate 5-HT1B agonist-induced PPI deficits and perseverative hyperlocomotion. These results may have implications for the etiology and treatment of OCD.

Serotonin receptor 1B (HTR1B) genotype associated with milk production traits in cattle

Serotonin receptor 1B (HTR1B) is one of the 14 different identified serotonin receptors which are involved in the regulation of behaviors such as sleep, fear, aggression, mood, and feeding. The aims of this study were to characterize polymorphisms in the 5' coding and the 3' flanking regions of the bovine HTR1B gene among Chinese Holsteins and to identify the association of HTR1B polymorphisms with milk production performance. SSCP was used to examine the polymorphisms at four loci and the fragments with different SSCP patterns were sequenced. A total of three single nucleotide polymorphisms (SNPs) were detected, among which the 205G>T mutation was found to cause a predicted amino acid change: from Ala to Ser at position 69. The polymorphism of G205T was identified to be associated with milk yield trait. Furthermore, the H1-C genotype was found to be associated with a significant increase in milk yield of 489kg vs. the H1-A genotype (P<0.05).

Evaluation of the serotonergic genes htr1A, htr1B, htr2A, and slc6A4 in aggressive behavior of golden retriever dogs

Aggressive behavior displays a high heritability in our study group of Golden Retriever dogs. Alterations in brain serotonin metabolism have been described in aggressive dogs before. Here, we evaluate whether four genes of the canine serotonergic system, coding for the serotonin receptors 1A, 1B, and 2A, and the serotonin transporter, could play a major role in aggression in Golden Retrievers. We performed mutation screens, linkage analysis, an association study, and a quantitative genetic analysis. There was no systematic difference between the coding DNA sequence of the candidate genes in aggressive and non-aggressive Golden Retrievers. An affecteds-only parametric linkage analysis revealed no strong major locus effect on human-directed aggression related to the candidate genes. An analysis of 41 single nucleotide polymorphisms (SNPs) in the 1 Mb regions flanking the genes in 49 unrelated human-directed aggressive and 49 unrelated non-aggressive dogs did not show association of SNP alleles, genotypes, or haplotypes with aggression at the candidate loci. We completed our analyses with a study of the effect of variation in the candidate genes on a collection of aggression-related phenotypic measures. The effects of the candidate gene haplotypes were estimated using the Restricted Maximum Likelihood method, with the haplotypes included as fixed effects in a linear animal model. We observed no effect of the candidate gene haplotypes on a range of aggression-related phenotypes, thus extending our conclusions to several types of aggressive behavior. We conclude that it is unlikely that these genes play a major role in the variation in aggression in the Golden Retrievers that we studied. Smaller phenotypic effects of these loci could not be ruled out with our sample size.

Meta-analyses suggest association between COMT, but not HTR1B, alleles, and suicidal behavior

Several studies have suggested that suicidal behavior is at least partially determined by genetic factors, supporting a search for related genes. Two genes that have been highlighted in the literature as being involved are HTR1B, which codes for the serotonin 1B receptor, and COMT, which is related to the inactivation of catecholamines. In order to assess the combined evidence for the numerous studies that have been published relating suicidal behavior to these two genes, two different random effects meta-analyses were conducted utilizing seven studies related to HTR1B and six studies related to COMT. For HTR1B, the combined evidence from 789 case and 1,247 control subjects/participants, suggested that there was no significant association between the HTR1B G861C polymorphism and suicidal behavior. For COMT, based on the combined data from 519 cases and 933 control subjects, there was evidence of a significant association between the COMT 158Met polymorphism and suicidal behavior. Although the results for COMT were not influenced by publication bias, the significance of the combined results was not robust and was related to the gender of the case and control subjects. The results for COMT support past literature that has found a relationship between suicidal behavior and COMT, and has also found that the relationship differs for males and females. Given that in the United States a higher proportion of females attempt suicide, and the higher proportion of males successfully commit suicide, it is possible that COMT is related to the lethality of suicide attempts.

5-hydroxytryptamine1B receptor and triptan response in migraine, lack of association with common polymorphisms

Triptans mediate vasoconstriction of meningeal vessels via stimulation of vascular 5-hydroxytryptamine (5-HT)(1B) receptors. These drugs are recommended for acute treatment in patients with moderate-to-severe migraine attacks and in those patients with mild-to-moderate headache that are not controlled adequately by other agents. Yet, approximately 25% of all migraine users and 40% of all attacks do not respond to triptan treatment. Among the hypothesis to explain this is the possibility that genetic single nucleotide polymorphisms that alter the receptor, for example changing the transcriptional rate and therefore the amount of target protein might change the clinical response to these drugs. In the present contribution, we therefore decided to evaluate whether single nucleotide polymorphisms on the 5-HT(1B) gene might contribute to inter-individual variability in clinical responses to triptans. Two polymorphisms in the promoter region of the 5-HT(1B) receptor (T-261G and A-161T) and the synonymous variation G861C in the coding region were genotyped by restriction fragment length polymorphism in 105 migraine patients. In our sample population, 71% of patients responded to triptans. Allelic and diplotype frequencies were not significantly different between responders and non-responders. On the other hand, extrapolation of in vitro data on promoter activity would suggest that patients with higher copy number of receptors respond slightly better. Our data therefore do not support the involvement of 5-HT(1B) single nucleotide polymorphisms in mediating the inter-individual variability to triptans.

Diplotypes of the human serotonin 1B receptor promoter predict growth hormone responses to sumatriptan in abstinent alcohol-dependent men

BACKGROUND

Some studies have associated alcohol dependence (AD) with the human serotonin (5-HT)(1B) receptor (HTR1B). This investigation explored the functional responsivity of HTR1B in abstinent AD men using a sumatriptan challenge, while measuring genetic heterogeneity in the HTR1B promoter.

METHODS

Abstinent AD men (n = 27) and abstinent men without any alcohol use disorder (n = 19) were administered 6 mg of sumatriptan succinate, subcutaneously. Plasma samples collected over the following 2 hours were assayed for growth hormone (GH) concentrations. His DNA was genotyped for the A-161T and T-261G polymorphisms of the HTR1B promoter and diplotypes determined.

RESULTS

Integrated GH responses were predicted by interactions of AD and promoter diplotypes, as well as subject ethnicity. The final model accounted for nearly 35% of the variance in GH responses. Post hoc evaluation revealed that AD was associated with a blunting of GH secretion only among individuals with the most common HTR1B diplotype (TT/TT).

CONCLUSIONS

A blunting of GH responses in abstinent AD men was observed only among those with the most common HTR1B promoter diplotype. Less common promoter diplotypes appeared protective. Controlling for genetic background is a useful augmentation of case-control pharmacological challenge strategies designed to elucidate the psychobiology of AD and other complex disorders.

Functional polymorphisms of the 5-HT1A and 5-HT1B receptor are associated with clinical symptoms in migraineurs

Migraine is regarded as a polygenic disease and serotonergic pathways appear to play a major role in its pathogenesis. In the present study, the role of the 5-HT1A and 5-HT1B receptors in migraine was evaluated. The human 5-HT1A receptor gene transcription is modulated by a functional C-1019G promoter polymorphism. The 5-HT1B receptor is the main effector of vasoconstriction in meningeal and cerebral arteries and its functional G861C promoter polymorphism was investigated. We report a positive association of the GG genotype of the 5-HT1A promoter polymorphism with avoidance of physical activity during a migraine attack in comparison to the CC genotype (p = 0.008). Moreover, a positive association of the CC genotype of the G861C polymorphism of the 5-HT1B receptor with the reported intensity of the headache attack on the visual analogue scale was observed (CC 8.3 +/- 1.5 vs. GG 6.9 +/- 1.8; p < 0.05). An association of either polymorphism with migraine with or without aura could not be found. For the first time, our results indicate a role of allelic variation of the 5-HT1A receptor in motion related discomfort in migraineurs and a role of the 5-HT1B receptor polymorphism in headache intensity.

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.

Why do young women smoke? II. Role of traumatic life experience, psychological characteristics and serotonergic genes

Cigarette smoking is a complex behavioral phenotype to which environmental, psychological and genetic factors contribute. The purpose of this study was to investigate these multifactorial effects with a specific focus on young women and on genes that encode serotonin (5-HT) receptors and the 5-HT transporter. A case-control sample of female Israeli college students provided comprehensive background data and details of cigarette smoking and completed a battery of psychological instruments. They were divided into smoking initiators (SI, n=242) or non-initiators (NI, n=148); SI were further subdivided into high (HND, n=127) and low nicotine-dependent smokers (LND, n=115) on the basis of their scores on the Fagerstrom Tolerance Questionnaire (FTQ). Single-nucleotide polymorphisms (SNPs) in five serotonin receptor genes (HTR1A, HTR1B, HTR2A, HTR2C and HTR6) and the 5-HT transporter-linked polymorphic region (5-HTTLPR) were genotyped. In a logistic regression model for SI (chi2=117.90, P=1.6 x 10(-19), Nagelkerke R2=0.42), novelty seeking (odds ratio (OR)=1.134, P=0.00009) was a significant risk factor. A five SNP CACCC haplotype in HTR6 was a strong protective factor against SI (OR=0.26; P=0.007). The interaction of HTR6-C276T genotype and lifetime traumatic experience contributed strongly to the risk of SI (OR=13.88, P=0.0001). Specifically, subjects homozygous for the HTR6-C276T C allele showed significantly increased risk of SI if they had experienced trauma. Although significant (chi2=42.85, P=1.00 x 10(-7)), the best-fitting model for ND was less predictive than the model for SI (Nagelkerke R2=0.24). HTR1B-G861C GG genotype (OR=2.29, P=0.01) was a significant risk factor for HND. Further studies should consider the interactive contribution of life events and relevant gene variants to cigarette smoking and other complex behavioral traits.

Genetics of suicide

The concept that genetic factors contribute to the complex trait of suicidal behaviour has stimulated much work aimed at identifying susceptibility genes. So far molecular genetic studies focused on the serotonergic pathway as the intent to die and the lethality of suicide acts were related to the serotonergic system. Two genes have so far emerged as being involved in the vulnerability for suicidality: first, the intronic polymorphisms (A218C or A779C) of the tryptophan hydroxylase 1 (TPH1) gene, which was suggested as a quantitative risk factor for suicidal behaviour; second, the insertion/deletion polymorphism of the serotonin transporter gene (5-HTTLPR), which does not seem to be involved in general suicidal behaviour, but in violent and repeated suicide attempts. The data have further shown that the MAOA gene, which is consistently associated with impulsive-aggressive personality traits, is not related to suicide but might induce violent methods in subjects with other suicide risk factors. Predominantly negative were the findings with any type of the serotonin receptors and inconsistent with catecholamine-synthesizing and -metabolizing enzymes or with the dopaminergic receptors. This paper reviews the status of current knowledge in this area, points to the weakness of the investigations and presents new approaches beyond the serotonergic system.

Association between the 5HT1B receptor gene (HTR1B) and the inattentive subtype of ADHD

BACKGROUND

Preclinical and genetic studies have implicated the 5HT1B receptor gene (HTR1B) in attention-deficit/hyperactivity disorder (ADHD). Association with a single nucleotide polymorphism (SNP; G861C) has been observed, but more extensive linkage disequilibrium analyses have not been reported.

METHODS

To examine haplotype structure, we genotyped 21 SNPs in and around the gene in 12 multigenerational CEPH pedigrees. We identified a haplotype block encompassing HTR1B and performed haplotype and single-marker association analyses for the eight SNPs within or flanking this block in 229 families of ADHD probands. In light of previous studies suggesting distinct genetic influences on ADHD subtypes, we also examined association with the inattentive and combined subtypes.

RESULTS

We observed nonsignificant overtransmission of the G861 allele to ADHD offspring (one-tailed p = .07). Single-marker and haplotype tests of a haplotype block encompassing HTR1B revealed no other associations with ADHD. However, this haplotype block was associated with the inattentive subtype (global p < .01). Additionally, three SNPs in this block were nominally (p < .05) associated with the inattentive subtype, although these did not remain significant after correction for multiple testing. As reported in previous studies, we found paternal overtransmission of the G861 allele to offspring with ADHD; this appeared to be largely attributable to inattentive cases.

CONCLUSIONS

These analyses suggest that variation in the HTR1B gene may primarily affect the inattentive subtype of ADHD.

5-HT1B receptors and aggression: A review

The serotonergic (5-HT) system in the brain is involved in the modulation of offensive aggressive behavior. The dogma that activity of the 5-HT system is inversely related to aggression is obsolete now. Research on the status of the 5-HT system before, during and after the execution of aggression is ongoing but has not yet led to a clear picture about the actual functional role of the 5-HT system, the more because state versus trait aggression seems to play a pivotal role in the outcome. Pharmacological challenges pinpoint 5-HT(1A) and 5-HT(1B) receptors as key players in the modulation of offensive aggression. This review emphasizes in particular the role of postsynaptic 5-HT(1B) (hetero) receptors as a premier site to modulate offensive aggression. Modulation of the firing and 5-HT release of the serotonergic neuron, via presynaptic 5-HT(1A) (auto) receptors, presynaptic 5-HT(1B) (auto) receptors and serotonergic transporters, may also have striking influences on aggression under certain conditions. Therefore, it is hypothesized that postsynaptic 5-HT(1B) (hetero) receptors directly influence the executive, consummatory phases of agonistic behavior, whereas presynaptic serotonergic feedback systems are particularly useful in the introductory (appetitive) phases of the agonistic behavioral complex.

Sex differences in the regulation of serotonergic transmission and behavior in 5-HT receptor knockout mice

Few studies have examined the relationship between genetics, stress, and sex-linked differences in neurotransmitter systems. Examining serotonin (5-HT) receptor knockout mice on stress-induced behavioral depression, female 5-HT1B receptor knockout mice demonstrated significantly reduced immobility than either male 5-HT1B receptor knockout mice or male and female wild-type mice on the tail suspension test (TST) and forced swimming test. The behavioral phenotype was identified as likely due to a disinhibition of 5-HT release, because depletion of 5-HT with parachlorophenylalanine selectively reduced immobility of female 5-HT1B receptor knockout mice in the TST. In contrast, male and female 5-HT1A receptor knockout mice demonstrated reduced immobility compared with control mice, but the depletion of 5-HT with PCPA did not reverse the antidepressant-like phenotype. Microdialysis studies confirmed significantly higher baseline levels of hippocampal 5-HT in female, but not male, 5-HT1B receptor knockout mice. Both male and female 5-HT1B receptor knockout mice demonstrated augmented dialysate responses to fluoxetine. Also, both male and female 5-HT1B receptor knockout mice demonstrated reductions of immobility in the TST after treatment with fluoxetine. Therefore, female 5-HT1B receptor knockout mice demonstrate a sex-linked disinhibition of 5-HT release that sustained higher baseline levels of hippocampal 5-HT and behavioral vulnerability to 5-HT depletion.

No association between the serotonin 1B receptor gene and schizophrenia in a case–control and family-based association study

Previous studies have demonstrated that polymorphisms in the putative promoter region of the human serotonin receptor 1B (HTR1B) gene affect gene expression [H.F. Sun, Y.T. Chang, C.S. Fann, C.J. Chang, Y.H. Chen, Y.P. Hsu, W.Y. Yu, A.T. Cheng, Association study of novel human serotonin 5-HT(1B) polymorphisms with alcohol dependence in Taiwanese Han, Biol. Psychiatry 51 (2002) 896-901; J. Duan, A.R. Sanders, J.E. Molen, L. Martinolich, B.J. Mowry, D.F. Levinson, R.R. Crowe, J.M. Silverman, P.V. Gejman, Polymorphisms in the 5'-untranslated region of the human serotonin receptor 1B (HTR1B) gene affect gene expression, Mol. Psychiatry 8 (2003) 901-910]. And the silent mutation G861C allele has been reported to be associated with several psychiatric disorders. Thus, we performed a case-control association study (456 cases and 557 controls) of the five variants in HTR1B gene (T-261G, -182INS/DEL-181, A-161T, C129T and G861C) with schizophrenia. The results showed that neither the allelic distribution nor the major haplotype distribution (except for a rare haplotype) of five SNPs in patients was significantly different from that in controls. A further family-based association study (229 family trios) of G861C allele suggested that HTR1B was not a susceptible gene with schizophrenia in our sample. In conclusion, these data do not support the idea that HTR1B gene plays a major role in the etiopathogenesis of schizophrenia in Chinese Han population.

Candidate genes for antidepressant response to selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) can safely and successfully treat major depression, although a substantial number of patients benefit only partially or not at all from treatment. Genetic polymorphisms may play a major role in determining the response to SSRI treatment. Nonetheless, it is likely that efficacy is determined by multiple genes, with individual genetic polymorphisms having a limited effect size. Initial studies have identified the promoter polymorphism in the gene coding for the serotonin reuptake transporter as moderating efficacy for several SSRIs. The goal of this review is to suggest additional plausible polymorphisms that may be involved in antidepressant efficacy. These include genes affecting intracellular transductional cascades; neuronal growth factors; stress-related hormones, such as corticotropin-releasing hormone and glucocorticoid receptors; ion channels and synaptic efficacy; and adaptations of monoaminergic pathways. Association analyses to examine these candidate genes may facilitate identification of patients for targeted alternative therapies. Determining which genes are involved may also assist in identifying future, novel treatments.

De novo complex chromosomal rearrangements (CCR) involving chromosome 1, 5, and 6 resulting in microdeletion for 6q14 in a female carrier with psychotic disorder

A 23-year-old obese woman with a psychotic disorder was found to have a de novo apparently balanced complex chromosomal rearrangement involving chromosomes 1, 5, and 6. Molecular cytogenetic analyses using high-resolution comparative genomic hybridization (HR-CGH) showed a microdeletion at 6q14 in a der(6). Application of HR-CGH facilitated detection of micro-rearrangement of all de novo apparently balanced complex chromosomal rearrangements (CCR) and supported the localization of the breakpoint. According to our knowledge, no constitutional interstitial microdeletion of chromosome 6q14 has been found associated with a schizoid-type phenotype.

Association between low-activity serotonin transporter genotype and heroin dependence: behavioral and personality correlates

In previous studies, serotonin (5-HT) system disturbance was found involved in a variety of behavioral disorders, psychopathologies, and substance use disorders. A functional polymorphism in the promoter region of the human serotonin transporter gene (5-HTTLPR) was recently identified and the presence of the short (S) allele found to be associated with a lower level of expression of the gene, lower levels of 5-HT uptake, type 2 alcoholism, violence and suicidal behavior. In the present study, 101 heroin addicts (males, West European, Caucasians) and 101 healthy control subjects matched for race and gender, with no history of substance use disorder, have been genotyped. Aggressiveness levels were measured in both heroin addicts and controls utilizing Buss-Durkee-Hostility-Inventory (BDHI). Data about suicide attempt and violent criminal behavior in subject history have been collected. The short-short (SS) genotype frequency was significantly higher among heroin dependent individuals compared with control subjects (P = 0.025). The odds ratio for the SS genotype versus the long-long (LL) genotype frequency was 0.69, 95% Cl (0.49-0.97), when heroin addicts were compared with healthy controls. The SS genotype frequency was significantly higher among violent heroin dependent individuals compared with addicted individuals without aggressive behavior (P = 0.02). BDHI mean total scores and suspiciousness and negativism subscales scores were significantly higher in SS individuals, in comparison with LL subjects, among heroin addicts. No association was found between SS genotype and suicide history. Our data suggest that a decreased expression of the gene encoding the 5-HTT transporter, due to "S" promoter polymorphism, may be associated with an increased risk for substance use disorders, particularly in the subjects with more consistent aggressiveness and impulsiveness.

Isolation and characterization of the canine serotonin receptor 1B gene (htr1B)

The serotonin receptor 1B gene (htr1B) has been suggested to be implicated in mental disorders in both humans and other species. We have isolated a canine bacterial artificial chromosome (BAC) clone containing htr1B, revealed the coding and surrounding DNA sequence of canine htr1B and designed primer sets for genomic sequencing of the gene. A mutation scan in 10 dogs revealed five single nucleotide polymorphisms in the htr1B coding sequence. By random sequencing of subclones of the BAC a polymorphic microsatellite repeat was found. We found evidence for at least four extended haplotypes in six dogs of the same breed. The chromosomal localization of the gene was confirmed by fluorescence in situ hybridisation and radiation hybrid mapping. This work provides a starting point for mutation scans and association studies on dogs with behavioural problems.

Polymorphisms in the 5'-untranslated region of the human serotonin receptor 1B (HTR1B) gene affect gene expression

We present evidence of complex balancing regulation of HTR1B transcription by common polymorphisms in its promoter. Computational analysis of the HTR1B gene predicted that a 5' segment, spanning common DNA sequence variations, T-261G, A-161T, and -182INS/DEL-181, contained a putative functional promoter. Using a secreted alkaline phosphatase (SEAP) reporter gene system, we found that the haplotype -261G_-182INS-181_A-161 enhanced transcriptional activity 2.3-fold compared with the haplotype T-261_-182INS-181_A-161. Conversely, -161T reversed this, and the net effect when -261G and -161T were in the same haplotype (-261G_-182INS-181_-161T) was equivalent to the major haplotype (T-261_-182INS-181_A-161). Electrophoretic mobility shift experiments showed that -261G and -161T modify the binding of transcription factors (TFs): -261G generates a new AP2 binding site, while alleles A-161 and -161T exhibit different binding characteristics to AP1. T-261G and A-161T were found to be in linkage disequilibrium (LD) with G861C in a European ancestry population. Interestingly, G861C has been reported to be associated with several psychiatric disorders. Our results indicate that HTR1B is the target of substantial transcriptional genetic regulation by common haplotypes, which are in LD with the HTR1B single-nucleotide polymorphism (SNP) most commonly used in association studies.

DNA variation and psychopharmacology of the human serotonin receptor 1B (HTR1B) gene

One of the neurotransmitter serotonin's receptors, HTR1B, is of interest for many neuropsychiatric traits, illnesses and treatments for multiple reasons, especially its tissue distribution, pharmacological profile and findings from mice lacking the receptor, along with reasons generally implicating serotonin. Eight mutation scans have uncovered sixteen polymorphisms in the coding sequence and surrounding 5'- and 3'-untranslated regions and much is now known of the distribution of these polymorphisms in various ethnic groups and their linkage disequilibrium relationships. Thus far, evidence exists that the uncommon missense T371G (Phe124Cys) and the common promoter region A-161T polymorphisms may exhibit functional effects and possibly that the common synonymous G861C (or more likely a variant in linkage disequilibrium with G861C) does as well. From the eighteen reported population-based case control studies of HTR1B to multiple disorders, several facts stand out. There exists preliminary evidence for association of G861C with i) antisocial alcoholism in the Finnish; ii) alcoholism in the presence of inactive aldehyde dehydrogenase 2 in the Japanese; iii) a history of suicide attempts in European-American personality disorder patients; and iv) minimum lifetime body mass index in Canadian bulimia nervosa patients. From the three reported family-based case control studies of HTR1B to various disorders, one provides preliminary evidence for association of G861C with obsessive compulsive disorder. Although many association studies have been completed, positive results should still be considered preliminary. As these preliminary reports are tested for replication with larger, more powerful samples, there should be increased clarity as to which findings remain robust; in some cases this will require the application of meta-analytic techniques.