The Cys allele of the DRD2 Ser311Cys polymorphism has a dominant effect on risk for schizophrenia: evidence from fixed- and random-effects meta-analyses

Ligand-directed bias of G protein signaling at the dopamine D2 receptor

G-protein-coupled receptors (GPCRs) represent the largest family of drug targets. Upon activation, GPCRs signal primarily via a diverse set of heterotrimeric G proteins. Most GPCRs can couple to several different G protein subtypes. However, how drugs act at GPCRs contributing to the selectivity of G protein recognition is poorly understood. Here, we examined the G protein selectivity profile of the dopamine D₂ receptor (D₂), a GPCR targeted by antipsychotic drugs. We show that D₂ discriminates between six individual members of the G_i/o family, and its profile of functional selectivity is remarkably different across its ligands, which all engaged D₂ with a distinct G protein coupling pattern. Using structural modeling, receptor mutagenesis, and pharmacological evaluation, we identified residues in the D₂ binding pocket that shape these ligand-directed biases. We further provide pharmacogenomic evidence that natural variants in D₂ differentially affect its G protein biases in response to different ligands.

A comprehensive in silico investigation into the nsSNPs of Drd2 gene predicts significant functional consequences in dopamine signaling and pharmacotherapy

DRD2 is a neuronal cell surface protein involved in brain development and function. Variations in the Drd2 gene have clinical significance since DRD2 is a pharmacotherapeutic target for treating psychiatric disorders like ADHD and schizophrenia. Despite numerous studies on the disease association of single nucleotide polymorphisms (SNPs) in the intronic regions, investigation into the coding regions is surprisingly limited. In this study, we aimed at identifying potential functionally and pharmaco-therapeutically deleterious non-synonymous SNPs of Drd2. A wide array of bioinformatics tools was used to evaluate the impact of nsSNPs on protein structure and functionality. Out of 260 nsSNPs retrieved from the dbSNP database, initially 9 were predicted as deleterious by 15 tools. Upon further assessment of their domain association, conservation profile, homology models and inter-atomic interaction, the mutant F389V was considered as the most impactful. In-depth analysis of F389V through Molecular Docking and Dynamics Simulation revealed a decline in affinity for its native agonist dopamine and an increase in affinity for the antipsychotic drug risperidone. Remarkable alterations in binding interactions and stability of the protein-ligand complex in simulated physiological conditions were also noted. These findings will improve our understanding of the consequence of nsSNPs in disease-susceptibility and therapeutic efficacy.

Genetic variants in dopamine receptors influence on heterodimerization in the context of antipsychotic drug action

Human dopamine D2 receptor (D₂R) gene has polymorphic variants, three of them alter its amino acid sequence: Val96Ala, Pro310Ser and Ser311Cys. Their functional role never became the object of extensive studies, even though there are some evidence that they correlate with schizophrenia. The present work reviews data indicating that these mutations play a role in dimer formation with dopamine D1 receptor (D₁R), with the strongest effect observed for Ser311Cys variant. Similarly, the affinity for antipsychotic drugs of this genetic variant depends on whether it is expressed together with D₁R or not. Better understanding of altered ability of genetic variants of D₂R to form dimers with D₁R, as well as of altered affinity for antipsychotic drugs, depending on the absence or presence of the second dopamine receptor is of great importance-since these two receptors are not always co-expressed in the same cell. It may well be that targeting new compounds toward the D₁R-D₂R dimers, which the most probably form under conditions of excessive dopamine release, will result in antipsychotic drugs devoid of serious side effects.

An epistasis between dopaminergic and oxytocinergic systems confers risk of post-traumatic stress disorder in a traumatized Chinese cohort

Post-traumatic stress disorder (PTSD) is a psychiatric syndrome that occurs after trauma exposure. Neurotransmitters such as dopamine and oxytocin have been reported to be involved in neuropathology of PTSD. Previous studies indicated that the dopamine–oxytocin interaction may contribute to behavioral disorders. Thus, exploring the epistasis (gene–gene interaction) between oxytocinergic and dopaminergic systems might be useful to reveal the genetic basis of PTSD. In this study, we analyzed two functional single nucleotide polymorphisms (SNPs), rs2268498 for oxytocinergic gene OXTR and rs1801028 for dopaminergic gene DRD2 based on putative oxytocin receptor–dopamine receptor D2 (OTR–DR2) heterocomplex in a Chinese cohort exposed to the 2008 Wenchuan earthquake (156 PTSD cases and 978 controls). Statistical analyses did not find any single variant or gene–environment interaction (SNP × earthquake-related trauma exposure) associated with provisional PTSD diagnosis or symptoms. An OXTR–DRD2 interaction (rs2268498 × rs1801028) was identified to confer risk of provisional PTSD diagnosis (OR = 9.18, 95% CI = 3.07–27.46 and P = 7.37e-05) and further subset analysis indicated that rs2268498 genotypes controlled the association directions of rs1801028 and rs1801028 genotypes also controlled the association directions of rs2268498. Rs2268498 × rs1801028 is also associated with PTSD symptoms (P = 0.043). Our study uncovered a genetic and putative function-based contribution of dopaminergic–oxytocinergic system interaction to PTSD.

Differential protein expression of DARPP-32 versus Calcineurin in the prefrontal cortex and nucleus accumbens in schizophrenia and bipolar disorder

Dopamine- and cAMP-regulated phosphoprotein of molecular weight 32 kDa (DARPP-32) integrates dopaminergic signaling into that of several other neurotransmitters. Calcineurin (CaN), located downstream of dopaminergic pathways, inactivates DARPP-32 by dephosphorylation. Despite several studies have examined their expression levels of gene and protein in postmortem patients’ brains, they rendered inconsistent results. In this study, protein expression levels of DARPP-32 and CaN were measured by enzyme-linked immunosorbent assay (ELISA) in the prefrontal cortex (PFC), and nucleus accumbens (NAc) of 49 postmortem samples from subjects with schizophrenia, bipolar disorder, and normal controls. We also examined the association between this expression and genetic variants of 8 dopaminergic system-associated molecules for 55 SNPs in the same postmortem samples. In the PFC of patients with schizophrenia, levels of DARPP-32 were significantly decreased, while those of CaN tended to increase. In the NAc, both of DARPP-32 and CaN showed no significant alternations in patients with schizophrenia or bipolar disorder. Further analysis of the correlation of DARPP-32 and CaN expressions, we found that positive correlations in controls and schizophrenia in PFC, and schizophrenia in NAc. In PFC, the expression ratio of DARPP-32/CaN were significantly lower in schizophrenia than controls. We also found that several of the aforementioned SNPs may predict protein expression, one of which was confirmed in a second independent sample set. This differential expression of DARPP-32 and CaN may reflect potential molecular mechanisms underlying the pathogenesis of schizophrenia and bipolar disorder, or differences between these two major psychiatric diseases.

An association study of dopaminergic (DRD2) and serotoninergic (5-HT2) gene polymorphism and schizophrenia in a North Indian population

The aim of this study was to investigate whether single nucleotide polymorphisms (SNPs) in DRD2 and 5-HT2 receptor genes are associated with schizophrenia in North Indian population. Four hundred forty-three patients who met ICD10-DCR criteria for schizophrenia were enrolled from six participating centers along with 443 genetically related healthy subjects and 150 genetically unrelated healthy participants. A total of 7 gene polymorphisms from DRD2 (rs1800497, rs1079597, rs1800498, rs1801028) and 5-HT2 A (rs6313, rs6311, rs6305) were genotyped for their association with schizophrenia. No significant difference was found in frequency of various genotypes and alleles of the studied markers for DRD2 and 5-HT2 A genes between the cases and their genetic controls. However, significant differences were noted for rs1079597 genotype (Taq1B; p = 0.039) and its allele frequencies (p = 0.029) in persons with schizophrenia and the unrelated healthy controls. The DRD2 (Taq1 A-B-D) and 5-HT2 A (rs6311-rs6313-rs6305) haplotype frequencies differed significantly for A2B1D2 [p = 0.038; OR = 0.685 (95%CI = 0.479-0.981)] and ACC [p = 0.001; OR = 0.621 (95%CI = 0.461-0.838)] for the cases vs genetically related healthy controls. Similarly, significant difference was observed for the frequencies of GCC [p = 0.006; OR = 0.692 (95%CI = 0.532-0.900)] and ACC [p < 0.001; OR = 3.622 (95%CI = 1.73-7.585)] in the cases and unrelated healthy controls. Unlike previous research from India as well as abroad, the predominance of B1 allele of rs1079597 in patients with schizophrenia and absence of Cys311 in all study participants is a salient difference. Concluding, the B2 allele of rs1079597 may increase the risk of schizophrenia while the A2B1D2 haplotype may be protective in North Indian population.

Antipsychotic Drug Responsiveness and Dopamine Receptor Signaling; Old Players and New Prospects

Antipsychotic drugs targeting dopamine neurotransmission are still the principal mean of therapeutic intervention for schizophrenia. However, about one third of people do not respond to dopaminergic antipsychotics. Genome wide association studies (GWAS), have shown that multiple genetic factors play a role in schizophrenia pathophysiology. Most of these schizophrenia risk variants are not related to dopamine or antipsychotic drugs mechanism of action. Genetic factors have also been implicated in defining response to antipsychotic medication. In contrast to disease risk, variation of genes coding for molecular targets of antipsychotics have been associated with treatment response. Among genes implicated, those involved in dopamine signaling mediated by D2-class dopamine receptor, including DRD2 itself and its molecular effectors, have been implicated as key genetic predictors of response to treatments. Studies have also reported that genetic variation in genes coding for proteins that cross-talk with DRD2 at the molecular level, such as AKT1, GSK3B, Beta-catenin, and PPP2R2B are associated with response to antipsychotics. In this review we discuss the relative contribution to antipsychotic drug responsiveness of candidate genes and GWAS identified genes encoding proteins involved in dopamine responses. We also suggest that in addition of these older players, a deeper investigation of new GWAS identified schizophrenia risk genes such as FXR1 can provide new prospects that are not clearly engaged in dopamine function while being targeted by dopamine-associated signaling molecules. Overall, further examination of genes proximally or distally related to signaling mechanisms engaged by medications and associated with disease risk and/or treatment responsiveness may uncover an interface between genes involved in disease causation with those affecting disease remediation. Such a nexus would provide realistic targets for therapy and further the development of genetically personalized approaches for schizophrenia.

A splicing-regulatory polymorphism in DRD2 disrupts ZRANB2 binding, impairs cognitive functioning and increases risk for schizophrenia in six Han Chinese samples

The rs1076560 polymorphism of DRD2 (encoding dopamine receptor D2) is associated with alternative splicing and cognitive functioning; however, a mechanistic relationship to schizophrenia has not been shown. Here, we demonstrate that rs1076560(T) imparts a small but reliable risk for schizophrenia in a sample of 616 affected families and five independent replication samples totaling 4017 affected and 4704 unaffected individuals (odds ratio=1.1; P=0.004). rs1076560(T) was associated with impaired verbal fluency and comprehension in schizophrenia but improved performance among healthy comparison subjects. rs1076560(T) also associated with lower D2 short isoform expression in postmortem brain. rs1076560(T) disrupted a binding site for the splicing factor ZRANB2, diminished binding affinity between DRD2 pre-mRNA and ZRANB2 and abolished the ability of ZRANB2 to modulate short:long isoform-expression ratios of DRD2 minigenes in cell culture. Collectively, this work implicates rs1076560(T) as one possible risk factor for schizophrenia in the Han Chinese population, and suggests molecular mechanisms by which it may exert such influence.

Biological mechanisms underlying evolutionary origins of psychotic and mood disorders

Psychotic and mood disorders are brain dysfunctions that are caused by gene environment interactions. Although these disorders are disadvantageous and involve behavioral phenotypes that decrease the reproductive success of afflicted individuals in the modern human society, the prevalence of these disorders have remained constant in the population. Here, we propose several biological mechanisms by which the genes associated with psychotic and mood disorders could be selected for in specific environmental conditions that provide evolutionary bases for explanations of when, why, and where these disorders emerged and have been maintained in humans. We discuss the evolutionary origins of psychotic and mood disorders with specific focuses on the roles of dopamine and serotonin in the conditions of social competitiveness/hierarchy and maternal care and other potential mechanisms, such as social network homophily and symbiosis.

Selection in the dopamine receptor 2 gene: a candidate SNP study

Dopamine is a major neurotransmitter in the human brain and is associated with various diseases. Schizophrenia, for example, is treated by blocking the dopamine receptors type 2. Shaner, Miller & Mintz (2004) stated that schizophrenia was the low fitness variant of a highly variable mental trait. We therefore explore whether the dopamine receptor 2 gene (DRD2) underwent any selection processes. We acquired genotype data of the 1,000 Genomes project (phase I), which contains 1,093 individuals from 14 populations. We included single nucleotide polymorphisms (SNPs) with two minor allele frequencies (MAFs) in the analysis: MAF over 0.05 and over 0.01. This is equivalent to 151 SNPs (MAF > 0.05) and 246 SNPs (MAF > 0.01) for DRD2. We used two different approaches (an outlier approach and a Bayesian approach) to detect loci under selection. The combined results of both approaches yielded nine (MAF > 0.05) and two candidate SNPs (MAF > 0.01), under balancing selection. We also found weak signs for directional selection on DRD2, but in our opinion these were too weak to draw any final conclusions on directional selection in DRD2. All candidates for balancing selection are in the intronic region of the gene and only one (rs12574471) has been mentioned in the literature. Two of our candidate SNPs are located in specific regions of the gene: rs80215768 lies within a promoter flanking region and rs74751335 lies within a transcription factor binding site. We strongly encourage research on our candidate SNPs and their possible effects.

The relationship between DRD2 gene polymorphisms (C957T and C939T) and schizophrenia: a meta-analysis

Schizophrenia is a common, complex multi-factorial psychiatric disorder. Many studies have reported associations between the C957T and C939T polymorphisms in Dopamine D2 receptor (DRD2) gene and schizophrenia, but results are inconsistent. To derive a more precise estimation of the relationship, a meta-analysis was conducted to systematically summarize the possibility. We included 13 articles involving 3079 schizophrenia cases and 3851 healthy controls. Positive associations were found between C957T polymorphism and schizophrenia risk in C vs. T (OR=1.26, 95% CI=1.09-1.46, Praw=0.002, PFDR=0.005) and CC+CT vs. TT (OR=1.47, 95% CI=1.25-1.73, Praw<0.001, PFDR<0.001). When stratified by race, a significantly increased risk of schizophrenia was observed in Caucasians, but not in Asians. No association between C939T polymorphism and schizophrenia was found in overall or Asian population. Our study suggested that C957T of DRD2 gene polymorphism is likely to be a risk factor for schizophrenia, especially in Caucasian.

Testosterone induces molecular changes in dopamine signaling pathway molecules in the adolescent male rat nigrostriatal pathway

Adolescent males have an increased risk of developing schizophrenia, implicating testosterone in the precipitation of dopamine-related psychopathology. Evidence from adult rodent brain indicates that testosterone can modulate nigrostriatal dopamine. However, studies are required to understand the role testosterone plays in maturation of dopamine pathways during adolescence and to elucidate the molecular mechanism(s) by which testosterone exerts its effects. We hypothesized that molecular indices of dopamine neurotransmission [synthesis (tyrosine hydroxylase), breakdown (catechol-O-methyl transferase; monoamine oxygenase), transport [vesicular monoamine transporter (VMAT), dopamine transporter (DAT)] and receptors (DRD1-D5)] would be changed by testosterone or its metabolites, dihydrotestosterone and 17β-estradiol, in the nigrostriatal pathway of adolescent male rats. We found that testosterone and dihydrotestosterone increased DAT and VMAT mRNAs in the substantia nigra and that testosterone increased DAT protein at the region of the cell bodies, but not in target regions in the striatum. Dopamine receptor D2 mRNA was increased and D3 mRNA was decreased in substantia nigra and/or striatum by androgens. These data suggest that increased testosterone at adolescence may change dopamine responsivity of the nigrostriatal pathway by modulating, at a molecular level, the capacity of neurons to transport and respond to dopamine. Further, dopamine turnover was increased in the dorsal striatum following gonadectomy and this was prevented by testosterone replacement. Gene expression changes in the dopaminergic cell body region may serve to modulate both dendritic dopamine feedback inhibition and reuptake in the dopaminergic somatodendritic field as well as dopamine release and re-uptake dynamics at the presynaptic terminals in the striatum. These testosterone-induced changes of molecular indices of dopamine neurotransmission in males are primarily androgen receptor-driven events as estradiol had minimal effect. We conclude that nigrostriatal responsivity to dopamine may be modulated by testosterone acting via androgen receptors to alter gene expression of molecules involved in dopamine signaling during adolescence.

Multivariate analysis of dopaminergic gene variants as risk factors of heroin dependence

BACKGROUND

Heroin dependence is a debilitating psychiatric disorder with complex inheritance. Since the dopaminergic system has a key role in rewarding mechanism of the brain, which is directly or indirectly targeted by most drugs of abuse, we focus on the effects and interactions among dopaminergic gene variants.

OBJECTIVE

To study the potential association between allelic variants of dopamine D2 receptor (DRD2), ANKK1 (ankyrin repeat and kinase domain containing 1), dopamine D4 receptor (DRD4), catechol-O-methyl transferase (COMT) and dopamine transporter (SLC6A3) genes and heroin dependence in Hungarian patients.

METHODS

303 heroin dependent subjects and 555 healthy controls were genotyped for 7 single nucleotide polymorphisms (SNPs) rs4680 of the COMT gene; rs1079597 and rs1800498 of the DRD2 gene; rs1800497 of the ANKK1 gene; rs1800955, rs936462 and rs747302 of the DRD4 gene. Four variable number of tandem repeats (VNTRs) were also genotyped: 120 bp duplication and 48 bp VNTR in exon 3 of DRD4 and 40 bp VNTR and intron 8 VNTR of SLC6A3. We also perform a multivariate analysis of associations using Bayesian networks in Bayesian multilevel analysis (BN-BMLA).

FINDINGS AND CONCLUSIONS

In single marker analysis the TaqIA (rs1800497) and TaqIB (rs1079597) variants were associated with heroin dependence. Moreover, -521 C/T SNP (rs1800955) of the DRD4 gene showed nominal association with a possible protective effect of the C allele. After applying the Bonferroni correction TaqIB was still significant suggesting that the minor (A) allele of the TaqIB SNP is a risk component in the genetic background of heroin dependence. The findings of the additional multiple marker analysis are consistent with the results of the single marker analysis, but this method was able to reveal an indirect effect of a promoter polymorphism (rs936462) of the DRD4 gene and this effect is mediated through the -521 C/T (rs1800955) polymorphism in the promoter.

Missense substitutions associated with behavioural disturbances in Alzheimer's disease (AD)

Behavioural and psychological symptoms in dementia, or BPSD, occur in the majority of Alzheimer's disease (AD) patients. They are associated with considerable patient morbidity and greater care-giver stress. There is some evidence suggesting that BPSD have a genetic component and a large number of studies have examined the association of candidate genes with these symptoms. This review provides a comprehensive summary of all the published studies investigating the association of candidate gene missense substitutions with BPSD. Missense substitutions could potentially alter protein function or render the protein non-functional, resulting in phenotypic consequences. More than 80 studies investigating the association of 8 missense substitutions in 7 genes with BPSD were identified. However, results of these studies are contradictory and do not provide firm support for these associations. Larger studies and more systematic approaches will delineate the association of missense substitutions with behavioural symptoms in AD.

Similarities and differences in peripheral blood gene-expression signatures of individuals with schizophrenia and their first-degree biological relatives

Several studies have evaluated the potential utility of blood-based whole-transcriptome signatures as a source of biomarkers for schizophrenia. This endeavor has been complicated by the fact that individuals with schizophrenia typically differ from appropriate comparison subjects on more than just the presence of the disorder; for example, individuals with schizophrenia typically receive antipsychotic medications, and have been dealing with the sequelae of this chronic illness for years. The inability to control such factors introduces a considerable degree of uncertainty in the results to date. To overcome this, we performed a blood-based gene-expression profiling study of schizophrenia patients (n = 9) as well as their unmedicated, nonpsychotic, biological siblings (n = 9) and unaffected comparison subjects (n = 12). The unaffected biological siblings, who may harbor some of the genetic predisposition to schizophrenia, exhibited a host of gene-expression differences from unaffected comparison subjects, many of which were shared by their schizophrenic siblings, perhaps indicative of underlying risk factors for the disorder. Several genes that were dysregulated in both individuals with schizophrenia and their siblings related to nucleosome and histone structure and function, suggesting a potential epigenetic mechanism underlying the risk state for the disorder. Nonpsychotic siblings also displayed some differences from comparison subjects that were not found in their affected siblings, suggesting that the dysregulation of some genes in peripheral blood may be indicative of underlying protective factors. This study, while exploratory, illustrated the potential utility and increased informativeness of including unaffected first-degree relatives in research in pursuit of peripheral biomarkers for schizophrenia.

Identification of genetic loci underlying the phenotypic constructs of autism spectrum disorders

OBJECTIVE

To investigate the underlying phenotypic constructs in autism spectrum disorders (ASD) and to identify genetic loci that are linked to these empirically derived factors.

METHOD

Exploratory factor analysis was applied to two datasets with 28 selected Autism Diagnostic Interview-Revised (ADI-R) algorithm items. The first dataset was from the Autism Genome Project (AGP) phase I (1,236 ASD subjects from 618 families); the second was from the AGP phase II (804 unrelated ASD subjects). Variables derived from the factor analysis were then used as quantitative traits in genome-wide variance components linkage analyses.

RESULTS

Six factors, namely, joint attention, social interaction and communication, nonverbal communication, repetitive sensory-motor behavior, peer interaction, and compulsion/restricted interests, were retained for both datasets. There was good agreement between the factor loading patterns from the two datasets. All factors showed familial aggregation. Suggestive evidence for linkage was obtained for the joint attention factor on 11q23. Genome-wide significant evidence for linkage was obtained for the repetitive sensory-motor behavior factor on 19q13.3.

CONCLUSIONS

This study demonstrates that the underlying phenotypic constructs based on the ADI-R algorithm items are replicable in independent datasets, and that the empirically derived factors are suitable and informative in genetic studies of ASD.

All roads to schizophrenia lead to dopamine supersensitivity and elevated dopamine D2(high) receptors

BACKGROUND

The dopamine D2 receptor is the common target for antipsychotics, and the antipsychotic clinical doses correlate with their affinities for this receptor. Antipsychotics quickly enter the brain to occupy 60-80% of brain D2 receptors in patients (the agonist aripiprazole occupies up to 90%), with most clinical improvement occurring within a few days. The D2 receptor can exist in a state of high-affinity (D2(High) ) or in a state of low-affinity for dopamine (D2Low).

AIM

The present aim is to review why individuals with schizophrenia are generally supersensitive to dopamine-like drugs such as amphetamine or methyphenidate, and whether the D2(High) state is a common basis for dopamine supersensitivity in the animal models of schizophrenia.

RESULTS

All animal models of schizophrenia reveal elevations in D2(High) receptors. These models include brain lesions, sensitization by drugs (amphetamine, phencyclidine, cocaine, corticosterone), birth injury, social isolation, and gene deletions in pathways for NMDA, dopamine, GABA, acetylcholine, and norepinephrine.

CONCLUSIONS

These multiple abnormal pathways converge to a final common pathway of dopamine supersensitivity and elevated D2(High) receptors, presumably responsible for psychotic symptoms. Although antipsychotics alleviate psychosis and reverse the elevation of D2(High) receptors, long-term antipsychotics can further enhance dopamine supersensitivity in patients. Therefore, switching from a traditional antipsychotic to an agonist antipsychotic (aripiprazole) can result in psychotic signs and symptoms. Clozapine and quetiapine do not elicit parkinsonism or tardive dyskinesia because they are released from D2 within 12 to 24 h. Traditional antipsychotics remain attached to D2 receptors for days, preventing relapse, but allowing accumulation that can lead to tardive dyskinesia. Future goals include imaging D2(High) receptors and desensitizing them in early-stage psychosis.

Association of common copy number variants at the glutathione S-transferase genes and rare novel genomic changes with schizophrenia

Copy number variants (CNVs) are a substantial source of human genetic diversity, influencing the variable susceptibility to multifactorial disorders. Schizophrenia is a complex illness thought to be caused by a number of genetic and environmental effects, few of which have been clearly defined. Recent reports have found several low prevalent CNVs associated with the disease. We have used a multiplex ligation-dependent probe amplification-based (MLPA) method to target 140 previously reported and putatively relevant gene-containing CNV regions in 654 schizophrenic patients and 604 controls for association studies. Most genotyped CNVs (95%) showed very low (<1%) population frequency. A few novel rare variants were only present in patients suggesting a possible pathogenic involvement, including 1.39 Mb overlapping duplications at 22q11.23 found in two unrelated patients, and duplications of the somatostatin receptor 5 gene (SSTR5) at 16p13.3 in three unrelated patients. Furthermore, among the few relatively common CNVs observed in patients and controls, the combined analysis of gene copy number genotypes at two glutathione S-transferase (GST) genes, GSTM1 (glutathione S-transferase mu 1) (1p13.3) and GSTT2 (glutathione S-transferase theta 2) (22q11.23), showed a statistically significant association of non-null genotypes at both loci with an additive effect for increased vulnerability to schizophrenia (odds ratio of 1.92; P=0.0008). Our data provide complementary evidences for low prevalent, but highly penetrant chromosomal variants associated with schizophrenia, as well as for common CNVs that may act as susceptibility factors by disturbing glutathione metabolism.

The neuregulin signaling pathway and schizophrenia: from genes to synapses and neural circuits

Numerous genetic linkage and association studies implicate members of the Neuregulin-ErbB receptor (NRG-ErbB) signaling pathway as schizophrenia "at risk" genes. An emphasis of this review is to propose plausible neurobiological mechanisms, regulated by the Neuregulin-ErbB signaling network, that may be altered in schizophrenia and contribute to its etiology. To this end, the distinct neurotransmitter pathways, neuronal subtypes and neural network systems altered in schizophrenia are initially discussed. Next, the review focuses on the possible significance of genetic studies associating NRG1 and ErbB4 with schizophrenia, in light of the functional role of this signaling pathway in regulating glutamatergic, GABAergic and dopaminergic neurotransmission, as well as modulating synaptic plasticity and gamma oscillations. The importance of restricted ErbB4 receptor expression in GABAergic interneurons is emphasized, particularly their expression at glutamatergic synapses of parvalbumin-positive fast-spiking interneurons where modulation of inhibitory drive could account for the dramatic effects of NRG-ErbB signaling on gamma oscillations and pyramidal neuron output. A case is made for reasons that the NRG-ErbB signaling pathway constitutes a "biologically plausible" system for understanding the pathogenic mechanisms that may underlie the complex array of positive, negative and cognitive deficits associated with schizophrenia during development.

Genetics and intermediate phenotypes of the schizophrenia--bipolar disorder boundary

Categorization of psychotic illnesses into schizophrenic and affective psychoses remains an ongoing controversy. Although Kraepelinian subtyping of psychosis was historically beneficial, modern genetic and neurophysiological studies do not support dichotomous conceptualization of psychosis. Evidence suggests that schizophrenia and bipolar disorder rather present a clinical continuum with partially overlapping symptom dimensions, neurophysiology, genetics and treatment responses. Recent large scale genetic studies have produced inconsistent findings and exposed an urgent need for re-thinking phenomenology-based approach in psychiatric research. Epidemiological, linkage and molecular genetic studies, as well as studies in intermediate phenotypes (neurocognitive, neurophysiological and anatomical imaging) in schizophrenia and bipolar disorders are reviewed in order to support a dimensional conceptualization of psychosis. Overlapping and unique genetic and intermediate phenotypic signatures of the two psychoses are comprehensively recapitulated. Alternative strategies which may be implicated into genetic research are discussed.

Comparative sequence and structural analyses of G-protein-coupled receptor crystal structures and implications for molecular models

BACKGROUND

Up until recently the only available experimental (high resolution) structure of a G-protein-coupled receptor (GPCR) was that of bovine rhodopsin. In the past few years the determination of GPCR structures has accelerated with three new receptors, as well as squid rhodopsin, being successfully crystallized. All share a common molecular architecture of seven transmembrane helices and can therefore serve as templates for building molecular models of homologous GPCRs. However, despite the common general architecture of these structures key differences do exist between them. The choice of which experimental GPCR structure(s) to use for building a comparative model of a particular GPCR is unclear and without detailed structural and sequence analyses, could be arbitrary. The aim of this study is therefore to perform a systematic and detailed analysis of sequence-structure relationships of known GPCR structures.

METHODOLOGY

We analyzed in detail conserved and unique sequence motifs and structural features in experimentally-determined GPCR structures. Deeper insight into specific and important structural features of GPCRs as well as valuable information for template selection has been gained. Using key features a workflow has been formulated for identifying the most appropriate template(s) for building homology models of GPCRs of unknown structure. This workflow was applied to a set of 14 human family A GPCRs suggesting for each the most appropriate template(s) for building a comparative molecular model.

CONCLUSIONS

The available crystal structures represent only a subset of all possible structural variation in family A GPCRs. Some GPCRs have structural features that are distributed over different crystal structures or which are not present in the templates suggesting that homology models should be built using multiple templates. This study provides a systematic analysis of GPCR crystal structures and a consistent method for identifying suitable templates for GPCR homology modelling that will help to produce more reliable three-dimensional models.

Family-based association testing strongly implicates DRD2 as a risk gene for schizophrenia in Han Chinese from Taiwan

The gene that codes for dopamine receptor D2 (DRD2 on chromosome 11q23) has long been a prime functional and positional candidate risk gene for schizophrenia. Collectively, prior case-control studies found a reliable effect of the Ser311Cys DRD2 polymorphism (rs1801028) on risk for schizophrenia, but few other polymorphisms in the gene had ever been evaluated and no adequately powered family-based association study has been performed to date. Our objective was to test 21 haplotype-tagging and all three known nonsynonymous single-nucleotide polymorphisms (SNPs) in DRD2 for association with schizophrenia in a family-based study of 2408 Han Chinese, including 1214 affected individuals from 616 families. We did not find a significant effect of rs1801028, but we did find significant evidence for association of schizophrenia with two multi-marker haplotypes spanning blocks of strong linkage disequilibrium (LD) and nine individual SNPs (Ps<0.05). Importantly, two SNPs (rs1079727 and rs2283265) and both multi-marker haplotypes spanning entire LD blocks (including one that contained rs1801028) remained significant after correcting for multiple testing. These results further add to the body of data implicating DRD2 as a schizophrenia risk gene; however, a causal variant(s) in DRD2 remains to be elucidated by further fine mapping of the gene, with particular attention given to the area surrounding the third through fifth exons.

Alternatively Spliced Genes as Biomarkers for Schizophrenia, Bipolar Disorder and Psychosis: A Blood-Based Spliceome-Profiling Exploratory Study

OBJECTIVE: Transcriptomic biomarkers of psychiatric diseases obtained from a query of peripheral tissues that are clinically accessible (e.g., blood cells instead of post-mortem brain tissue) have substantial practical appeal to discern the molecular subtypes of common complex diseases such as major psychosis. To this end, spliceome-profiling is a new methodological approach that has considerable conceptual relevance for discovery and clinical translation of novel biomarkers for psychiatric illnesses. Advances in microarray technology now allow for improved sensitivity in measuring the transcriptome while simultaneously querying the "exome" (all exons) and "spliceome" (all alternatively spliced variants). The present study aimed to evaluate the feasibility of spliceome-profiling to discern transcriptomic biomarkers of psychosis. METHODS: We measured exome and spliceome expression in peripheral blood mononuclear cells from 13 schizophrenia patients, nine bipolar disorder patients, and eight healthy control subjects. Each diagnostic group was compared to each other, and the combined group of bipolar disorder and schizophrenia patients was also compared to the control group. Furthermore, we compared subjects with a history of psychosis to subjects without such history. RESULTS: After applying Bonferroni corrections for the 21,866 full-length gene transcripts analyzed, we found significant interactions between diagnostic group and exon identity, consistent with group differences in rates or types of alternative splicing. Relative to the control group, 18 genes in the bipolar disorder group, eight genes in the schizophrenia group, and 15 genes in the combined bipolar disorder and schizophrenia group appeared differentially spliced. Importantly, thirty-three genes showed differential splicing patterns between the bipolar disorder and schizophrenia groups. More frequent exon inclusion and/or over-expression was observed in psychosis. Finally, these observations are reconciled with an analysis of the ontologies, the pathways and the protein domains significantly over-represented among the alternatively spliced genes, several of which support prior discoveries. CONCLUSIONS: To our knowledge, this is the first blood-based spliceome-profiling study of schizophrenia and bipolar disorder to be reported. The battery of alternatively spliced genes and exons identified in this discovery-oriented exploratory study, if replicated, may have potential utility to discern the molecular subtypes of psychosis. Spliceome-profiling, as a new methodological approach in transcriptomics, warrants further work to evaluate its utility in personalized medicine. Potentially, this approach could also permit the future development of tissue-sampling methodologies in a form that is more acceptable to patients and thereby allow monitoring of dynamic and time-dependent plasticity in disease severity and response to therapeutic interventions in clinical psychiatry.

Genetic variants of D2 but not D3 or D4 dopamine receptor gene are associated with rapid onset and poor prognosis of methamphetamine psychosis

D2-like receptors are key targets for methamphetamine in the CNS, and their activation is an initial and indispensable effect in the induction of dependence and psychosis. It is possible that genetic variants of D2-like receptors may affect individual susceptibility to methamphetamine dependence and psychosis. To test this hypothesis, 6 putatively functional polymorphisms of D2-like receptors, -141C Ins/Del, Ser311Cys and TaqIA of the DRD2 gene, Ser9Gly of the DRD3 gene, and -521C>T and a variable number of tandem repeats in exon 3 of the DRD4 gene, were analyzed in 202 patients with methamphetamine dependence and/or psychosis and 243 healthy controls in a Japanese population. No polymorphism examined showed significant association with methamphetamine dependence, but two polymorphisms of DRD2 were associated with the clinical course and prognosis of methamphetamine psychosis. The A1/A1 homozygote of DRD2 was a negative risk factor for a poorer prognosis of psychosis that continues for more than 1 month after the discontinuance of methamphetamine abuse and the beginning of treatment with neuroleptics (p=0.04, odds ratio (OR)=0.42, 95% CI; 0.27-0.65) and the complication of spontaneous relapse of methamphetamine psychosis after remission (p=0.014, OR=0.34, 95% CI; 0.22-0.54). The genotype of -141C Del positive (Del/Del and Del/Ins) was at risk for rapid onset of methamphetamine psychosis that develops into a psychotic state within 3 years after initiation of methamphetamine abuse (p=0.00037, OR=3.62, 95% CI 2.48-5.28). These findings revealed that genetic variants of DRD2, but not DRD3 or DRD4, confer individual risks for rapid onset, prolonged duration, and spontaneous relapse of methamphetamine psychosis.

Genetic susceptibility to schizophrenia: role of dopaminergic pathway gene polymorphisms

Aim: We investigated 16 polymorphisms from three genes, dopamine receptor D2 (DRD2), catechol-O-methyl transferase (COMT) and brain derived neurotrophic factor (BDNF), which are involved in the dopaminergic pathways, and have been reported to be associated with susceptibility to schizophrenia and response to antipsychotic therapy. Materials & methods: Single-locus association analyses of these polymorphisms were carried out in 254 patients with schizophrenia and 225 controls, all of southern Indian origin. Additionally, multifactor-dimensionality reduction analysis was performed in 422 samples (243 cases and 179 controls) to examine the gene–gene interactions and to identify combinations of multilocus genotypes associated with either high or low risk for the disease. Results: Our results demonstrated initial significant associations of two SNPs for DRD2 (rs11608185, genotype: χ2 = 6.29, p-value = 0.043; rs6275, genotype: χ2 = 8.91, p-value = 0.011), and one SNP in the COMT gene (rs4680, genotype: χ2 = 6.67, p-value = 0.035 and allele: χ2 = 4.75, p-value = 0.029; odds ratio: 1.33, 95% confidence interval: 1.02–1.73), but not after correction for multiple comparisons indicating a weak association of individual markers of DRD2 and COMT with schizophrenia. Multifactor-dimensionality reduction analysis suggested a two locus model (rs6275/DRD2 and rs4680/COMT) as the best model for gene–gene interaction with 90% cross-validation consistency and 42.42% prediction error in predicting disease risk among schizophrenia patients. Conclusion: The present study thus emphasizes the need for multigene interaction studies in complex disorders such as schizophrenia and to understand response to drug treatment, which could lead to a targeted and more effective treatment.

Case-control association study of 59 candidate genes reveals the DRD2 SNP rs6277 (C957T) as the only susceptibility factor for schizophrenia in the Bulgarian population

The development of molecular psychiatry in the last few decades identified a number of candidate genes that could be associated with schizophrenia. A great number of studies often result with controversial and non-conclusive outputs. However, it was determined that each of the implicated candidates would independently have a minor effect on the susceptibility to that disease. Herein we report results from our replication study for association using 255 Bulgarian patients with schizophrenia and schizoaffective disorder and 556 Bulgarian healthy controls. We have selected from the literatures 202 single nucleotide polymorphisms (SNPs) in 59 candidate genes, which previously were implicated in disease susceptibility, and we have genotyped them. Of the 183 SNPs successfully genotyped, only 1 SNP, rs6277 (C957T) in the DRD2 gene (P=0.0010, odds ratio=1.76), was considered to be significantly associated with schizophrenia after the replication study using independent sample sets. Our findings support one of the most widely considered hypotheses for schizophrenia etiology, the dopaminergic hypothesis.

Genetic associations with schizophrenia: meta-analyses of 12 candidate genes

Genetic association studies on schizophrenia (SZ) have been repeatedly performed over the last two decades, resulting in a consensus that results are generally inconsistent. This consensus has begun to change as a result of meta-analyses (e.g., [Glatt, S.J. and Jonsson, E.G., 2006. The Cys allele of the DRD2 Ser311Cys polymorphism has a dominant effect on risk for schizophrenia: evidence from fixed- and random-effects meta-analyses. Am. J. Med. Genet. B. Neuropsychiatr. Genet. 141, 149-154.]). The SchizophreniaGene database (http://www.schizophreniaforum.org/res/sczgene/default.asp) has been a leader in meta-analyses of SZ association data, by dynamically and comprehensively cataloging all public genetic association studies, and preparing meta-analyses of case-control data. There are 19 "top" candidate genes from these analyses (access on December 20, 2007), showing the highest effect sizes and nominally significant associations of at least one variant in the meta-analyses of all ethnic samples or of samples of Caucasian ancestry. We selected 40 polymorphisms in 12 selected "top" genes for additional meta-analyses, which had at least one familial association data. We found gene-wide (correction for the number of meta-analyses for each gene) significant allelic association evidence for seven genes in the combined samples. The odds ratios (ORs) of the associated minor risk alleles range from 1.072 to 1.121, for DRD4, MTHFR, PPP3CC and TP53. For protective allele associations, the ORs are between 0.842 and 0.886, for DAO, IL1B, and SLC6A4. In population-based sub-analyses, we found significant results in four genes in Asians (ORs between 1.084 and 1.309 for DRD4, GABRB2, PPP3CC, and TP53), and one gene in European (OR of 0.888 for SLC6A4). The association of rs1816072 of GABRB2 with SZ in Asians was significant (adjusted P=0.048 after correction for 80 tests). No significant heterogeneity between case-control and family-based study designs was detected in 35 out of 40 polymorphisms. Our results further support eight potential SZ candidate genes and suggest that family data can reasonably be included in the meta-analysis of genetic associations.

Association study of three polymorphisms in the dopamine D2 receptor gene and schizophrenia in the Russian population

Polymorphisms in the dopamine D2 receptor gene (DRD2) have repeatedly been associated with schizophrenia. Recently, the C957T polymorphism (rs6277), which alters mRNA stability and dopamine-induced upregulation of DRD2 expression in cell cultures and DRD2 mRNA translation in vitro, was tested for an association with the disease. Frequency of the C allele, corresponding to a normal wild-type level of expression, was higher in patients compared to controls, and that of the T allele was lower. To replicate and extend previous findings, we conducted an association study of the C957T polymorphism and two additional SNPs (C939T and TaqIA) in 311 patients with a DSM-IV diagnosis of schizophrenia and 364 mentally healthy people from the Russian population as controls. The results of our study confirmed the association between the C957T polymorphism and schizophrenia. Consistent with previous findings, frequency of the C allele and the CC genotype were higher in patients compared to the control group (p=0.002). Meta-analysis of total 5 samples also suggests significant allelic association. The distribution of C939T genotypes in the case sample was significantly different from that of the controls: in the case sample, the TT genotype frequency was higher compared to the combined frequency of CT and CC genotypes (p=0.002). Though no association was found between the TaqIA polymorphism and schizophrenia, a haplotype-wise analysis revealed a lower frequency of the T-C (C957T-TaqIA) haplotype in patients (p=0.02). In conclusion, our findings provide additional evidence for an association between the C957T polymorphism and schizophrenia.

A lesson not learned: allele misassignment

Misassigned alleles can annihilate efforts to control quality in otherwise well-designed genetic association analyses. To date, the issue remains underreported, as is exemplified by studies of a diallelic DRD2 missense variant in schizophrenia. For this variant, allele frequency data have been either misassigned, or incorrectly cited on four consecutive occasions. Contrary to conjecture, low heterozygosity has not guarded against the error with regard to rs1801028, a SNP that features a canonical base pair transversion, G:C. Measures are discussed that may help to identify misassigned alleles, and to avoid related perils pending more systematic investigation of this confounder in genotype-phenotype associations.

Dopamine genes and schizophrenia: case closed or evidence pending?

The dopamine hypothesis of schizophrenia (SZ) has motivated a large number of genetic association studies but few if any dopaminergic (DA) polymorphisms are accepted as credible risk factors at present. To evaluate whether dopamine-related genes have been investigated adequately, we surveyed public genetic databases and published SZ association studies with regard to 14 conventional DA genes and 7 selected dopamine-interacting proteins. We estimate that 325 polymorphisms would be required to evaluate the impact of common variation on SZ risk among Caucasian samples. To date, 98 polymorphisms have been analyzed in published association studies. We estimate that only 19 of these variations have been evaluated in samples with at least 50% power to detect an association of the effect size commonly found in genetically complex disorders. While it is possible that DA genes do not harbor genetic risk factors for SZ, our review suggests that satisfactory conclusions for most genes cannot be drawn at present. Whole-genome association studies have begun to fill this void, but additional analyses are likely to be needed. Recommendations for future association studies include analysis of adequately powered samples, judiciously selected polymorphisms, multiple ethnic groups, and concurrent evaluation of function at associated single-nucleotide polymorphisms.

Potential genetic variants in schizophrenia: a Bayesian analysis

A number of different gene polymorphisms have been found to dispose for the development of schizophrenia. However, no single gene polymorphism is sufficient for the precipitation of schizophrenia. Swedish psychosis patients (n=103) and control subjects (n=89) were analyzed for 36 single nucleotide polymorphisms in 30 candidate genes for schizophrenia. Evidence of association was analyzed with Bayesian statistical methods. Variants in the genes coding for dopamine-D2 receptor, brain-derived neurotrophic factor (BDNF), neuropeptide Y (NPY), neuregulin 1, reelin and synapsin 3 showed association with schizophrenia, although few subjects were found in the minority allele for the two latter variants. The six gene variants, all with suspected connection to schizophrenia, were found to be risk factors when considered in combination, but not separately. The results indicate that the Bayesian statistical method gives additional possibilities in the search for risk factors for schizophrenia or other complex disorders.

G protein-coupled receptors in major psychiatric disorders

Although the molecular mechanisms underlying psychiatric illnesses such as depression, bipolar disorder and schizophrenia remain incompletely understood, there is increasing clinical, pharmacologic, and genetic evidence that G protein-coupled receptors (GPCRs) play critical roles in these disorders and their treatments. This perspectives paper reviews and synthesizes the available data. Dysfunction of multiple neurotransmitter and neuropeptide GPCRs in frontal cortex and limbic-related regions, such as the hippocampus, hypothalamus and brainstem, likely underlies the complex clinical picture that includes cognitive, perceptual, affective and motoric symptoms. The future development of novel agents targeting GPCR signaling cascades remains an exciting prospect for patients refractory to existing therapeutics.

Targeting the dopamine D2 receptor in schizophrenia

After a 12-year search for the antipsychotic receptor, the binding site was discovered and labelled by [3H]haloperidol in 1975. Of the various neurotransmitters, dopamine was the most potent in inhibiting the binding of [3H]haloperidol, indicating that the antipsychotic receptor was a dopamine receptor, now named the dopamine D2 receptor, a major targeting site in schizophrenia. All antipsychotic drugs, including traditional and newer antipsychotics, either bind to D2 in direct relation to their clinical potencies or hinder normal dopamine neurotransmission, as in the case of partial dopamine agonists. In fact, the antipsychotic concentrations found in the plasma water of treated patients closely match the predicted therapeutic absolute concentrations, adjusted for the 60-75% D2 occupancy needed for clinical efficacy. Antipsychotics that elicit low or no Parkinsonism or prolactinaemia are loosely attached to D2 and rapidly dissociate from D2, whereas those eliciting Parkinsonism stay tightly attached to D2 for many hours. Because animal models of psychosis (amfetamine sensitisation, brain lesions) all show a marked elevation in the number of high-affinity states of D2, the antipsychotics are thought to specifically target these D2High states in psychosis in general and schizophrenia in particular.

Amphetamine sensitization elevates CaMKIIß mRNA

Recent studies have shown that the elevation in calcium/calmodulin-dependent protein kinase II (CaMKII) may play an important role in amphetamine-induced dopamine release, as well as in the increase of dopamine D2 receptor high-affinitystates in psychosis. Because amphetamine sensitization is a widely used animal model of psychosis or schizophrenia, we investigated whether amphetamine sensitization results in an overall increase in the alpha and beta subunits of CaMKII. To answer this question, we measured CaMKII alpha and beta subunit mRNA expression using Real-Time Quantitative PCR in amphetamine-sensitized rat striata, compared to saline-treated controls. The results were then standardized to beta-glucuronidase, a housekeeping gene. Our results showed a statistically significant increase in the CaMKII beta subunit, and an increase in the alpha subunit which did not reach statistical significance. Because the levels of both CaMKIIbeta and CaMKIIalpha play a role in neuronal function and synapse formation, the present finding of an elevated level of CaMKII beta and alpha subunit mRNA in the amphetamine-sensitized model of psychosis points to the possibility of dysregulated levels of CaMKII subunits in human psychosis.

Psychosis pathways converge via D2high dopamine receptors

The objective of this review is to identify a target or biomarker of altered neurochemical sensitivity that is common to the many animal models of human psychoses associated with street drugs, brain injury, steroid use, birth injury, and gene alterations. Psychosis in humans can be caused by amphetamine, phencyclidine, steroids, ethanol, and brain lesions such as hippocampal, cortical, and entorhinal lesions. Strikingly, all of these drugs and lesions in rats lead to dopamine supersensitivity and increase the high-affinity states of dopamine D2 receptors, or D2High, by 200-400% in striata. Similar supersensitivity and D2High elevations occur in rats born by Caesarian section and in rats treated with corticosterone or antipsychotics such as reserpine, risperidone, haloperidol, olanzapine, quetiapine, and clozapine, with the latter two inducing elevated D2High states less than that caused by haloperidol or olanzapine. Mice born with gene knockouts of some possible schizophrenia susceptibility genes are dopamine supersensitive, and their striata reveal markedly elevated D2High states; suchgenes include dopamine-beta-hydroxylase, dopamine D4 receptors, G protein receptor kinase 6, tyrosine hydroxylase, catechol-O-methyltransferase, the trace amine-1 receptor, regulator of G protein signaling RGS9, and the RIIbeta form of cAMP-dependent protein kinase (PKA). Striata from mice that are not dopamine supersensitive did not reveal elevated D2High states; these include mice with knockouts of adenosine A2A receptors, glycogen synthase kinase GSK3beta, metabotropic glutamate receptor 5, dopamine D1 or D3 receptors, histamine H1, H2, or H3 receptors, and rats treated with ketanserin or aD1 antagonist. The evidence suggests that there are multiple pathways that convergetoelevate the D2High state in brain regions and that this elevation may elicit psychosis. This proposition is supported by the dopamine supersensitivity that is a common feature of schizophrenia and that also occurs in many types of genetically altered, drug-altered, and lesion-altered animals. Dopamine supersensitivity, in turn, correlates with D2High states. The finding that all antipsychotics, traditional and recent ones, act on D2High dopamine receptors further supports the proposition.