The serotonin transporter gene 5-HTTLPR polymorphism is associated with affective psychoses but not with schizophrenia: A large-scale study in the Russian population

The Neurobiological Underpinnings of Obsessive-Compulsive Symptoms in Psychosis, Translational Issues for Treatment-Resistant Schizophrenia

Almost 25% of schizophrenia patients suffer from obsessive-compulsive symptoms (OCS) considered a transdiagnostic clinical continuum. The presence of symptoms pertaining to both schizophrenia and obsessive-compulsive disorder (OCD) may complicate pharmacological treatment and could contribute to lack or poor response to the therapy. Despite the clinical relevance, no reviews have been recently published on the possible neurobiological underpinnings of this comorbidity, which is still unclear. An integrative view exploring this topic should take into account the following aspects: (i) the implication for glutamate, dopamine, and serotonin neurotransmission as demonstrated by genetic findings; (ii) the growing neuroimaging evidence of the common brain regions and dysfunctional circuits involved in both diseases; (iii) the pharmacological modulation of dopaminergic, serotoninergic, and glutamatergic systems as current therapeutic strategies in schizophrenia OCS; (iv) the recent discovery of midbrain dopamine neurons and dopamine D1- and D2-like receptors as orchestrating hubs in repetitive and psychotic behaviors; (v) the contribution of N-methyl-D-aspartate receptor subunits to both psychosis and OCD neurobiology. Finally, we discuss the potential role of the postsynaptic density as a structural and functional hub for multiple molecular signaling both in schizophrenia and OCD pathophysiology.

Association Study of BDNF, SLC6A4, and FTO Genetic Variants with Schizophrenia Spectrum Disorders

Schizophrenia spectrum disorders (patients with a diagnosis of schizophrenia, schizotypal, and delusional disorders: F20-F29 according to International Classification of Diseases 10th revision (ICD-10)) are considered highly heritable heterogeneous psychiatric conditions. Their pathophysiology is multifactorial with involved dysregulated serotonergic neurotransmission and synaptic plasticity. The present study aimed to evaluate the association of SLC6A4 (5-HTTLPR), FTO (rs9939609), and BDNF (rs6265, rs962369) polymorphisms with schizophrenia spectrum disorders in Slovak patients. We analyzed the genotypes of 150 patients with schizophrenia, schizotypal, and delusional disorders and compared them with genotypes from 178 healthy volunteers. We have found a marginally protective effect of LS + SS genotypes of 5-HTTLPR variant of the serotonin transporter SLC6A4 gene against the development of schizophrenia spectrum disorders, but the result failed to remain significant after Bonferroni correction. Similarly, we have not proven any significant association between other selected genetic variants and schizophrenia and related disorders. Studies including a higher number of subjects are warranted to reliably confirm the presence or absence of the studied associations.

A comparative study of theory of mind in taxon-like clusters of psychometric schizotypes and individuals at genetic risk for schizophrenia

Introduction: Clinical and family studies suggest that alterations of theory of mind (ToM) represent a marker of genetic liability to schizophrenia. Findings regarding ToM in schizotypy are less consistent. The study aimed to explore whether this might be due to an insufficient account of the heterogeneity of schizotypy in prior research and/or the fact that in psychometric schizotypy ToM alterations could manifest as subtle peculiarities rather than overt errors of mentalising.Methods: Individuals without a family history of psychosis (n = 150) were assigned to low, positive, negative, and high mixed schizotypy classes based on a cluster analysis of 1322 subjects who completed the Schizotypal Personality Questionnaire. The classes were compared on their performance of faux pas tasks with 77 adult first-degree relatives of schizophrenia patients, who represent individuals at genetic risk for schizophrenia. Besides overt errors, subtle alterations in ToM were analysed using expert judgment.Results: The relatives tended to make overt errors and demonstrated specific features of intentional reasoning. None of the schizotypal classes showed similar trends.Conclusions: The results complement the literature on the subjective-objective disjunction in psychometric schizotypes and did not provide evidence that ToM anomalies are a marker of genetic liability to schizophrenia in this cohort.

Serotonin transporter functional polymorphisms potentially increase risk of schizophrenia separately and as a haplotype

Schizophrenia is a severe, disabling psychiatric disorder with unclear etiology. Family-based, twins, and adoption studies have shown that genetic factors have major contributions in schizophrenia occurrence. Until now, many studies have discovered the association of schizophrenia and its comorbid symptoms with functional polymorphisms that lie within serotonin reuptake pathway genes. Here, we aimed to investigate the association of three variable number tandem repeats (VNTR) functional polymorphisms in MAOA and SLC6A4 with schizophrenia in the Iranian population. Two hundred and forty-one subjects with schizophrenia and three hundred and seventy age and sex-matched healthy controls were genotyped for MAOA promoter uVNTR, 5-HTTLPR, and STin2 polymorphisms. Genotyping was performed by polymerase chain reaction (PCR) with locus-specific primers and running the PCR product on agarose 2.5% gel electrophoresis. Finally, the statistical inference was performed using R programming language and Haploview software. MAOA promoter uVNTR analysis of allele frequency showed no differences between schizophrenia subjects and healthy controls in both males and females and no significant differences were observed between female cases and female controls in MAOA promoter uVNTR 4 repeat frequency. Also, there were no differences between Schizophrenia and healthy control groups in 5-HTTLPR allele and genotype frequency but, 5-HTTLPR S allele carriers are significantly more frequent among cases. In addition, STin2.12 repeats were significantly more frequent among schizophrenia patients. Genotype comparison suggested that 5-HTTLPR S allele and STin2.12 repeat carriers were significantly more frequent among schizophrenia cases and being STin2.12 repeat carrier significantly increase the risk of schizophrenia occurrence. Besides, analysis of haplotype showed stronger linkage disequilibrium between 5-HTTLPR and STin2 haplotype block in cases than controls. These results suggest that SLC6A4 functional polymorphisms potentially could play a possible role as risk factors for the incidence of schizophrenia.

[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.

Effect of the C-reactive protein gene on risk and clinical characteristics of schizophrenia in winter-born individuals

C-reactive protein (CRP) levels are elevated in a subset of schizophrenia patients and correlated with more severe symptoms, which makes CRP a potential theranostic biomarker for the disease. However, genotypes associated with higher CRP concentrations have the protective effect against schizophrenia. To resolve this discrepancy, more research on the role of CRP in schizophrenia is needed. The present study aimed to investigate the effects on schizophrenia of the CRP gene in combination with season of birth (SOB), the known risk factor for the disease. We first examined the impact of seasonality on schizophrenia risk in the Russian population, using samples of 2452 patients and 1203 controls, and then assessed the CRP rs2794521 polymorphism × SOB interaction effect on the disease risk, age-of-onset and symptoms severity in 826 patients and 476 controls. An excess of winter births in patients was not significant. At the same time, we found that winter-born patients carrying the CRP GG genotype, which is associated with low transcriptional activity, had an earlier age at onset than the other patients. The findings are in line with the protective role of high active CRP genetic variants in the development of schizophrenia and provide support for the hypothesis that this effect of CRP takes place early in life.

Opening up new horizons for psychiatric genetics in the Russian Federation: moving toward a national consortium

We provide an overview of the recent achievements in psychiatric genetics research in the Russian Federation and present genotype-phenotype, population, epigenetic, cytogenetic, functional, ENIGMA, and pharmacogenetic studies, with an emphasis on genome-wide association studies. The genetic backgrounds of mental illnesses in the polyethnic and multicultural population of the Russian Federation are still understudied. Furthermore, genetic, genomic, and pharmacogenetic data from the Russian Federation are not adequately represented in the international scientific literature, are currently not available for meta-analyses and have never been compared with data from other populations. Most of these problems cannot be solved by individual centers working in isolation but warrant a truly collaborative effort that brings together all the major psychiatric genetic research centers in the Russian Federation in a national consortium. For this reason, we have established the Russian National Consortium for Psychiatric Genetics (RNCPG) with the aim to strengthen the power and rigor of psychiatric genetics research in the Russian Federation and enhance the international compatibility of this research.The consortium is set up as an open organization that will facilitate collaborations on complex biomedical research projects in human mental health in the Russian Federation and abroad. These projects will include genotyping, sequencing, transcriptome and epigenome analysis, metabolomics, and a wide array of other state-of-the-art analyses. Here, we discuss the challenges we face and the approaches we will take to unlock the huge potential that the Russian Federation holds for the worldwide psychiatric genetics community.

[Genetic variations associated with premorbid personality in patients with schizophrenia]

AIM

To search for genetic variants associated with premorbid personality in patients with schizophrenia.

MATERIAL AND METHODS

The sample included 272 men diagnosed with schizophrenia or schizoaffective disorder. Patients were divided into 3 groups based on premorbid personality difficulties: mild (group 1, n=110), moderate (group 2, n=113), marked (group 3, n=49). The following polymorphisms were genotyped: 5-HTR2A (T102C), 5-HTTLPR, BDNF (Val66Met), CRP (-717A>G).

RESULTS

A significant increase in the frequency of the CC (5-HTR2A T102C), LL (5-HTTLPR) and Met/Met (BDNF Val66Met) genotypes was identified in group 3 compared to group 1. Frequencies of CC and LL genotypes were significantly higher in group 2 compared to group 1 as well. The differences between group 2 and group 3 were found only for the Met/Met genotype. There were no between-group differences in the frequencies of CRP (-717A>G) genotypes.

CONCLUSION

5-HTR2A (T102C), 5-HTTLPR, BDNF (Val66Met) polymorphisms previously reported to modify schizophrenia course are also associated with premorbid personality in schizophrenic patients.

Effects of a GWAS-Supported Schizophrenia Variant in the DRD2 Locus on Disease Risk, Anhedonia, and Prefrontal Cortical Thickness

The study aimed to confirm the association of the schizophrenia genome-wide association study (GWAS) hit rs2514218 located near the DRD2 gene with the risk of the disease and to investigate the relationships between rs2514218 and schizophrenia-related clinical and neuroimaging phenotypes. Genotypes at the rs2514218 site were determined for 2148 schizophrenia spectrum patients and 1273 control subjects from the Russian population. In subsets of subjects, we assessed symptomatic dimensions using the Positive and Negative Syndrome Scale (n = 1651) and Temporal Experience of Pleasure Scale (n = 471). At the brain level, gray matter volumes in striatal structures and cortical thickness in the lateral prefrontal cortical regions were investigated (n = 97). Genotype frequencies did not differ between patients and controls. The allelic association analysis yielded a near-threshold p value (p = 0.054), the magnitude (OR = 0.90), and direction of the minor allele (T) effect being in accord with those in the schizophrenia GWAS. Also, patients homozygous for the risk allele C had more severe consummatory anhedonia and a thinner cortex than controls and patients carrying the T allele. The largest effect size of the genotype with diagnosis interaction was seen in the right pars opercularis area. The findings support the role of rs2514218 in schizophrenia risk and presentation and suggest rs2514218 has an influence on brain morphology and negative symptoms.

Relationship between Alzheimer's disease-associated SNPs within the CLU gene, local DNA methylation and episodic verbal memory in healthy and schizophrenia subjects

Genetic variation may impact on local DNA methylation patterns. Therefore, information about allele-specific DNA methylation (ASM) within disease-related loci has been proposed to be useful for the interpretation of GWAS results. To explore mechanisms that may underlie associations between Alzheimer's disease (AD) and schizophrenia risk CLU gene and verbal memory, one of the most affected cognitive domains in both conditions, we studied DNA methylation in a region between AD-associated SNPs rs9331888 and rs9331896 in 72 healthy individuals and 73 schizophrenia patients. Using single-molecule real-time bisulfite sequencing we assessed the haplotype-dependent ASM in this region. We then investigated whether its methylation could influence episodic verbal memory measured with the Rey Auditory Verbal Learning Test in these two cohorts. The region showed a complex methylation pattern, which was similar in healthy and schizophrenia individuals and unrelated to haplotypes. The pattern predicted memory scores in controls. The results suggest that epigenetic modifications within the CLU locus may play a role in memory variation, independent of ASM.

Association between the SLC6A4 gene and schizophrenia: an updated meta-analysis

BACKGROUND

In order to explore the association between the SLC6A4 gene and the risk of schizophrenia, an updated meta-analysis was conducted using a total of 46 scientific articles.

METHODS

Through a literature search, papers studied included 35 articles on serotonin-transporter-linked polymorphic region (5-HTTLPR) with 8,752 cases and 10,610 controls, 17 articles on second intron variable number of tandem repeats with 7,284 cases and 8,544 controls, four studies on rs1042173 with 1,351 cases and 2,101 controls, and four studies on rs140700 with 1,770 cases and 2,386 controls. Pooled, subgroup, and sensitivity analyses were performed, and the results were visualized by forest and funnel plots.

RESULTS

An association between 5-HTTLPR and the risk of schizophrenia was not found, except for an Indian subgroup analysis (P_z =0.014, OR =1.749, 95% CI =1.120-2.731). A 10 repeats/12 repeats (10R/12R) genotype was a protective factor against schizophrenia (P_z =0.020, OR =0.789, 95% CI =0.646-0.963), but a 12R/12R genotype was a risk factor for schizophrenia (P_z =0.004, OR =1.936, 95% CI =1.238-3.029) in the pooled analyses. In Caucasians, a GG genotype of rs1042173 may be a risk factor for schizophrenia (P_z =0.006, OR =1.299, 95% CI =1.079-1.565). No association was found between rs140700 and the risk for schizophrenia.

CONCLUSION

Through meta-analysis, we were able to gain insight into previously reported associations between SLC6A4 polymorphism and schizophrenia.