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

Global research in schizophrenia and serotonin: a bibliometric analysis

Background

Schizophrenia is a chronic mental illness that affects millions of individuals worldwide. The etiological origin of schizophrenia is heterogeneous, but it has been shown to be associated with dysfunction in serotonin activity, serotonin receptors, and serotonin metabolism in the brain. Bibliometric analysis is a tool used to scrutinise and analyse research activities and evidence in a specific research area. No existing bibliometric analyses have considered both serotonin and schizophrenia.

Methods

We conducted a bibliometric analysis including 12,027 studies related to the schizophrenia-serotonin link published from the inception of the study to 2023 and available in the Scopus database. We used VOSviewer software to identify global trends, analyse the author and editors keywords, the most cited articles and author, as well as the most productive institutes and journals publishing research on schizophrenia-serotonin link.

Results

Most publications related to the link between schizophrenia and serotonin are focused on adult humans and examine topics such as antipsychotic agents, depression, and serotonin uptake inhibitors. The Journal of Clinical Psychiatry has published the most papers on the schizophrenia-serotonin relationship. Among nations, the United States is the leader in publications. King's College London is the institution with the highest number of publications, and H. Y. Meltzer is the most influential author. Growing trends in schizophrenia-serotonin research are personalised medicine, alternative medicine, transcranial magnetic stimulation, artificial intelligence, nervous system inflammation, brain-gut axis, and the gut microbiome.

Conclusion

Since 1950, there have been several fluctuations in the number of published studies related to schizophrenia and serotonin. We believe that the development of novel medications and treatments for schizophrenia will be increased in the future, as well as research into genetic risks, psychological factors, and cranial neuroimaging components. Future schizophrenia and serotonin research is likely to focus on personalised medicine, alternative therapies, novel pathogenesis of schizophrenia, and the use of emerging technologies such as artificial intelligence.

[Prognosis of the functional outcome of schizophrenia using a multigene panel]

OBJECTIVE

To compare the groups of schizophrenic patients with different levels of functional outcome and different frequency of risk variants in polymorphic loci of five candidate genes to create a multigene panel and to test its predictive ability for long-term outcome of the disease.

MATERIAL AND METHODS

According to the proposed typology, the patients included in the studies were divided into three groups, which differed in the level of social functioning. Group 1 was characterized by the highest level, in group 2 this indicator was significantly lower, and in group 3 the lowest. The multigenic panel included genes for serotonin receptor type 2a (5-HTR2A T102C), serotonin transporter (5-HTTLPR), C-reactive protein (CRP -717A>G), angiotensin II receptor type 1 (AGTR1 A1166C), and brain neurotrophic factor (BDNF Val66Met). A multi-gene risk score was calculated for each patient by summing the total number all his/her risk alleles. For each polymorphism, a score of 2 was assigned to homozygous high-risk genotypes, a score of 1 to heterozygous genotypes and a score of 0 to homozygous low-risk genotype. Accordingly, the multi-gene risk score for a patient could vary from 0 to 10 risk alleles.

RESULTS

A significant effect of the group on the multi-gene risk score was shown (p<0.0001). Between-group differences were significant as well (p<0.01). In group 1, there were no carriers of ≥6 risk alleles, and the number of carriers of less than 5 alleles exceeded 50%. In group 2, the number of carriers of ≥6 risk alleles was 19.4%, and in group 3 - 31.7%. Moreover, in these groups there were no carriers of 0-2 risk alleles, while in group 1 their number was 20.7%.

CONCLUSION

The multi-gene risk score predicts the level of functional outcome in patients with schizophrenia. In the case of a smaller number of risk alleles (0-4) in an individual, a favorable functional outcome can be predicted with a high probability in the long-term period of the disease.

Meta-analysis of polymorphism rs6311 and rs6313 in the 5-HT2AR gene and schizophrenia

BACKGROUND

rs6311 and rs6313 polymorphism of 5-hydroxytryptamine 2A receptor has been widely studied regarding association with susceptibility to schizophrenia, but the results remained inconsistent.

AIMS

This study aimed to assess the association between rs6311 and rs6313 polymorphism and schizophrenia using a meta-analysis.

METHODS

Pubmed, Web of Science, and Embase databases were searched for all articles linking rs6311 and rs6313 polymorphism and schizophrenia. All studies which met the inclusion and exclusion criteria were included in this meta-analysis. Pooled odds ratio and 95% confidence intervals were used to evaluate the association between rs6311 and rs6313 polymorphism and schizophrenia risk. Sub-group analysis was also performed by different ethnic studies (Asian and Caucasian) and different minor allelic studies (rs6311: minor allele = A and minor allele = G; rs6313: minor allele = T and minor allele = C).

RESULTS

Forty articles, including 50 case-control studies, were included in this meta-analysis. Specifically, 12 studies with 4100 cases and 4541 controls involved rs6311, 38 studies with 8960 cases and 9729 controls involved rs6313. The results showed that rs6311 and rs6313 were not associated with schizophrenia. Moreover, no associations were found between rs6311 and schizophrenia in different sub-groups, rs6313 was found to associated with schizophrenia among studies in which C is the minor allele.

CONCLUSIONS

This meta-analysis indicates that rs6311 and rs6313 polymorphisms of 5-HT_2AR are not associated with schizophrenia. However, the rs6313 polymorphism is associated with schizophrenia in studies in which the minor allele is C.

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.

Yokukansan, a traditional Japanese medicine, decreases head-twitch behaviors and serotonin 2A receptors in the prefrontal cortex of isolation-stressed mice

ETHNOPHARMACOLOGICAL RELEVANCE

Yokukansan, a traditional Japanese (Kampo) medicine, has recently been used to treat the behavioral and psychological symptoms of dementia (BPSD), including aggressiveness, excitability, and hallucination. The present study was designed to investigate the mechanisms underlying the ameliorative effects of yokukansan on BPSD using animals exhibiting hallucination-like behaviors. For this purpose, we initially examined whether chronic isolation stress increases the frequency of hallucination in response to a psychedelic drug. Using this animal model, we next examined the effects of yokukansan on drug-induced hallucination-like behaviors. Finally, we examined the density and mRNA levels of serotonin 2A (5-HT2A) receptors.

MATERIALS AND METHODS

Male mice were subjected to isolation stress for six weeks. Yokukansan was incorporated into food pellets, and administered to the mice for six weeks. In some experiments, yokukansan and each of seven constituent herbs were administered orally to the mice for the last two weeks during the six-week period of isolation stress. A 5-HT2A receptor agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI, 2.5mg/kg), was injected into the mice, and head-twitch behaviors were quantified. The binding sites of 5-HT2A receptors on the plasma membrane of the prefrontal cortex (PFC) were assessed by a receptor-binding assay using tritium-labeled ketanserin, and the density and affinity were calculated from a Scatchard plot. The level of mRNAs was measured by PCR analyses.

RESULTS

Isolation stress enhanced the frequency of the DOI-induced head-twitch response, and yokukansan treatment by feeding significantly reduced this enhancement. Isolation stress significantly increased the 5-HT2A receptor density in the PFC, and yokukansan treatment by feeding as well as administration significantly down-regulated this increase. Isolation stress and yokukansan did not affect the affinity. Among seven constituent herbs, Bupleurum Root, Uncaria Hook, Japanese Angelica Root, and Glycyrrhiza down-regulated the increase, but statistically not significant, in which their efficacies were over 50% relative to yokukansan. Neither isolation stress nor yokukansan affected mRNA levels of 5-HT2A receptors.

CONCLUSION

Yokukansan attenuated drug-induced hallucination-like behaviors in isolated mice, which is suggested to be mediated by 5-HT2A receptor down-regulation in the PFC. This mechanism may underlie the ameliorative effects of yokukansan on hallucination.

[Youth-onset schizophrenia: psychopathology, clinical presentation and therapy]

The paper reviews the clinical presentations and pathogenetic features of youth-onset schizophrenia with onset at the age of 16-25 years old. The clinical presentation of the disease in young people is different in comparison to adult patients. Psychopathological and biological characteristics of the first episode, the course of «progressive» schizophrenia and «malignant youth schizophrenia» in the pubertal period are described. Early diagnosis and prevention of disease manifestation are discussed. Recommendations on therapeutic measures at different stages of the endogenous process in this age are presented. The most important future goals of research in this field are formulated.

Abnormal kalirin signaling in neuropsychiatric disorders

Changes in dendritic spines structure and function play a critical role in a number of physiological processes, including synaptic transmission and plasticity, and are intimately linked to cognitive function. Alterations in dendritic spine morphogenesis occur in a number of neuropsychiatric disorders and likely underlie the cognitive and behavioral changes associated with these disorders. The neuronal guanine nucleotide exchange factor (GEF) kalirin is emerging as a key regulator of structural and functional plasticity at dendritic spines. Moreover, a series of recent studies have genetically and functionally linked kalirin signaling to several disorders, including schizophrenia and Alzheimer's disease. Kalirin signaling may thus represent a disease mechanism and provide a novel therapeutic target.

Association of schizophrenia with T102C (rs6313) and 1438 A/G (rs6311) polymorphisms of HTR2A gene

OBJECTIVE

The aim of this study is to investigate whether there were any associations between the T102C and 1438 A/G polymorphisms of the 5-HT2A receptor gene and schizophrenia. We conducted a case-control study of the T102C and 1438 A/G polymorphisms in Turkish patients.

METHODS

We compared genotypes and allele frequencies of T102C and 1438 A/G polymorphisms of 5-HT2A receptor gene in 102 patients with schizophrenia diagnosed, according to DSM-IV, and 107 healthy controls. Genotyping was performed by real-time polymerase chain reaction.

RESULTS

We found no significant association between schizophrenia and genotypic or allele frequencies of HTR2A gene 102T/C (rs6313) and 1438 A/G (6311) polymorphisms. However, comparison of HTR2A gene 102 T/C and 1438 A/G polymorphisms in terms of genotypic and allele frequencies between the two patient groups, with or without a family history of schizophrenia, shows that T- and A-allele frequencies were significantly higher (p < 0.05) in the case group that has a history of schizophrenia in their family.

CONCLUSION

In conclusion, our results do not support the hypothesis that the T102C and 1438 A/G polymorphisms in the 5-HT2A receptor gene are associated with schizophrenia, but further studies in a larger sample are needed.

T102C polymorphism of serotonin 2A type receptor gene confers susceptibility to (early onset) schizophrenia in Han Chinese: an association study and meta-analysis

INTRODUCTION

Several lines of evidence have indicated that serotonin 2A receptor (HTR2A) may be involved in the pathophysiology of schizophrenia. One functional polymorphism in HTR2A (T102C) has been widely investigated; however, the results have been inconsistent. The purpose of this study was to evaluate the association between HTR2A T02C polymorphism and schizophrenia in a Chinese Han population.

METHODS

We performed a case-control study, using an early onset sample, which may be an attractive subgroup for genetic studies. In addition, we performed a meta-analysis of the combined sample groups in Han Chinese.

RESULTS

Our study, based on 385 schizophrenic patients and 399 controls, found a significant genotype-wise association of T102C and schizophrenia (P = 0.02). After applying stratified analyses, the dominant model for T allele produced significant association (OR = 1.60, 95%CI = 1.11-2.30, P = 0.01). In the meta-analysis including all of the published population-based association studies in Han Chinese and the present association study, the pooled genotype-wise result in a dominant model was statistically significant with a summary OR of 1.25 (95%CI = 1.04-1.50, P = 0.02).

DISCUSSION

Our results suggest that the HTR2A T102C polymorphism may confer susceptibility to schizophrenia in Han Chinese.

Kalirin signaling: implications for synaptic pathology

Spine morphogenesis and plasticity are intimately linked to cognition, and there is strong evidence that aberrant regulation of spine plasticity is associated with physiological, behavioral, and pathological conditions. The neuronal guanine nucleotide exchange factor (GEF) kalirin is emerging as a key regulator of structural and functional plasticity at dendritic spines. Here, we review recent studies that have genetically and functionally linked kalirin signaling to a number of human disorders. Kalirin signaling may thus represent a disease mechanism and provide a novel therapeutic target.

Analysis of 94 candidate genes and 12 endophenotypes for schizophrenia from the Consortium on the Genetics of Schizophrenia

OBJECTIVE

The authors used a custom array of 1,536 single-nucleotide polymorphisms (SNPs) to interrogate 94 functionally relevant candidate genes for schizophrenia and identify associations with 12 heritable neurophysiological and neurocognitive endophenotypes in data collected by the Consortium on the Genetics of Schizophrenia.

METHOD

Variance-component association analyses of 534 genotyped subjects from 130 families were conducted by using Merlin software. A novel bootstrap total significance test was also developed to overcome the limitations of existing genomic multiple testing methods and robustly demonstrate significant associations in the context of complex family data and possible population stratification effects.

RESULTS

Associations with endophenotypes were observed for 46 genes of potential functional significance, with three SNPs at p<10(-4), 27 SNPs at p<10(-3), and 147 SNPs at p<0.01. The bootstrap analyses confirmed that the 47 SNP-endophenotype combinations with the strongest evidence of association significantly exceeded that expected by chance alone, with 93% of these findings expected to be true. Many of the genes interact on a molecular level, and eight genes (e.g., NRG1 and ERBB4) displayed evidence for pleiotropy, revealing associations with four or more endophenotypes. The results collectively support a strong role for genes related to glutamate signaling in mediating schizophrenia susceptibility.

CONCLUSIONS

This study supports use of relevant endophenotypes and the bootstrap total significance test for identifying genetic variation underlying the etiology of schizophrenia. In addition, the observation of extensive pleiotropy for some genes and singular associations for others suggests alternative, independent pathways mediating pathogenesis in the "group of schizophrenias."

Polymorphism of serotonin receptor genes (5-HTR2A) and Dysbindin (DTNBP1) and individual components of short-term verbal memory processes in Schizophrenia

Associations between polymorphisms in the T102C and A-1438G loci of the 5-HTR2A and the P1763 and P1578 markers of the DTNBP1 gene with the overall productivity and individual subprocesses of shortterm verbal memory were studied in 4-5 patients with schizophrenia and 290 healthy subjects. Subjects were asked to reproduce immediately two lists of 10 words. The overall productivity of reproduction was assessed, along with the reproduction productivity of the first list (immediate memory or general attention), the effect of proactive interference, and the number of intrusions. Patients were significantly different from controls on all measures. Patients showed decreases in overall task performance productivity, in immediate memory productivity, and in the effect of proactive interference; fewer intrusions were seen. Both markers of the 5-HTR2A gene were associated with short-term memory productivity in the combined cohort: assessments were worse in T102C CC and A-1438G GG homozygotes. The P1763 marker of the DTNBP1 gene, conversely, had significant influences on the memory subprocesses reflected in the levels of interference and intrusions but had insignificant influence on overall productivity. Homozygotes for P1763G GG had the worst parameters. Overall, these data are consistent with the concept that these polymorphic genes are involved in different subprocesses of short-term memory both in normal subjects and in patients with schizophrenia.

Association analysis of GRM2 and HTR2A with methamphetamine-induced psychosis and schizophrenia in the Japanese population

BACKGROUND

Abnormalities in glutaminergic neural transmission have been suggested to be involved in the pathogenesis of schizophrenia. A recent study reported that alterations in the 5-HT2A-mGluR2 complex may be involved in neural transmission in the schizophrenic cortex. In addition, methamphetamine-induced psychosis is thought to be similar to schizophrenia. Therefore, we conducted a case-control study with Japanese samples (738 schizophrenia patients, 196 methamphetamine-induced psychosis patients, and 802 controls) to evaluate the association and interaction between GRM2, HTR2A and schizophrenia.

METHODS

We selected three 'tagging SNPs' in GRM2, and two biologically functional SNPs in HTR2A (T102C and A1438G), for the association analysis.

RESULTS

We detected a significant association between methamphetamine-induced psychosis and GRM2 in a haplotype-wise analysis, but not HTR2A. We did not detect an association between GRM2 or HTR2A and schizophrenia. In addition, no interactions of GRM2 and HTR2A were found in methamphetamine-induced psychosis or schizophrenia. We did not detect any novel polymorphisms in GRM2 when we performed a mutation search using methamphetamine-induced psychosis samples.

CONCLUSION

Our results suggested that GRM2 may play a role in the pathophysiology of methamphetamine-induced psychosis but not schizophrenia in the Japanese population. A replication study using larger samples or samples of other populations will be required for conclusive results.

From genes to psychoses and back: the role of the 5HT2alpha-receptor and prepulse inhibition in schizophrenia

Decomposition of schizophrenia into neurobiological vulnerability traits is necessary to understand the complex genetic underpinnings of this phenomenologically defined disorder. This issue is discussed with a focus on prepulse inhibition (PPI) as a neurobiological phenotype and the 5HT2a-receptor as a candidate gene. A series of recent studies illuminates that PPI and 5HT2a-receptors present as vulnerability markers for schizophrenia; a functional sequence variant in the 5HT2a-gene is contributing to this relationship and might consequently contribute to the genetic predisposition to schizophrenia with a very small risk increase.

Sensorimotor gating of schizophrenia patients is influenced by 5-HT2A receptor polymorphisms

BACKGROUND

Schizophrenia patients exhibit impairment in prepulse inhibition (PPI) of the acoustic startle response (ASR), suggesting a sensorimotor gating deficit. The serotonin-2A receptor (5-HT(2A)R) has been implicated in both the pathogenesis of schizophrenia and the PPI deficits of schizophrenia patients. Moreover, both schizophrenia and PPI are thought to be inheritable. We investigated the impact of three 5-HT(2A)R polymorphisms (A-1438G, T102C, H452Y) on PPI in schizophrenia patients.

METHODS

We analyzed the 5-HT(2A)R A-1438G, T102C, and H452Y polymorphisms and assessed startle reactivity, habituation, and PPI of ASR in 68 Caucasian schizophrenia inpatients. Patients were also examined with the Positive and Negative Syndrome Scale.

RESULTS

The 5-HT(2A)R A-1438G and T102C polymorphisms were in complete linkage disequilibrium. Patients carrying the T102C TT and the A-1438G AA allele show significantly higher PPI levels and a faster early habituation compared with all other variants. 5-HT(2A)R A-1438G and T102C genotype explained approximately 11% of the PPI and early habituation variance. In contrast, the 5-HT(2A)R H452Y polymorphism did not affect startle parameters.

CONCLUSIONS

Our findings suggest that PPI and habituation are modulated by 5-HT(2A)R A-1438G and T102C genotype in schizophrenia. Consequently, alterations within brain 5-HT(2A)Rs may contribute to the PPI deficits in schizophrenia.

Excess of transmission of the G allele of the -1438A/G polymorphism of the 5-HT2A receptor gene in patients with schizophrenia responsive to antipsychotics

BACKGROUND

The -1438A/G polymorphism of the 5-HT2A gene has been found to be associated with clinical response to clozapine and other second generation antipsychotics. Testing the impact of this marker on response to first generation antipsychotics (which have a lower affinity for the 5-HT2A receptor) provides the opportunity to help disentangling the two different roles that this polymorphism might have. A psychopharmacogenetic role should be detected only for antipsychotics with high affinity to the 5-HT2A receptor (therefore to second generation antipsychotics). An alternative role would imply tagging a subgroup of patients responsive to any antipsychotic, whatever their affinity, meaning that the association is more depending on non pharmacological charaterictics, such as clinical specificities.

METHODS

A family-based sample of 100 Algerian patients with schizophrenia (according to DSM-IV criteria) and their 200 biological parents was recruited, in order to avoid stratification biases. Patients were all treated, or have been treated, by conventional antipsychotics (mainly haloperidol) for at least four weeks, at appropriate dosage. May and Dencker scale was used to distinguish responders and non responders.

RESULTS

No allele of the -1438A/G polymorphism of the 5-HT2A gene was transmitted in excess (50 transmitted for 38 untransmitted) in the whole sample of patients with schizophrenia (p = .90). In contrast, a significant excess of transmission of the G allele was observed (p = .02) in the subgroup of patients with good treatment response (17 transmitted for 6 untransmitted).

CONCLUSION

Using a TDT approach, we showed that the G allele of the -1438A/G polymorphism of the gene coding for the 5-HT2A receptor was associated to schizophrenia with good response to conventional antipsychotics, although this conclusion is based on 88 informative patients only. Because previous data showed the same result with atypical antipsychotics, it can be concluded that the G allele tags a subgroup of schizophrenic patients with greater chance of improvement with antipsychotics of either type.