An association study of dopamine receptors polymorphisms and the Wisconsin Card Sorting Test in schizophrenia

Association of 11 variants of the dopaminergic and cognitive pathways genes with major depression, schizophrenia and bipolar disorder in the Pakistani population

Background: The dopaminergic pathways control neural signals that modulate mood and behaviour along and have a vital role in the aetiology of major depression (MDD), schizophrenia (SHZ) and bipolar disorder (BD). Genome-wide association studies (GWAS) have reported several dopaminergic and cognitive pathway genes association with these disorders however, no such comprehensive data was available regarding the Pakistani population.Objective: The present study was conducted to analyse the 11 genetic variants of dopaminergic and cognitive system genes in MDD, SHZ, and BD in the Pakistani population.Methods: A total of 1237 subjects [MDD n = 479; BD n = 222; SHZ n = 146; and controls n = 390], were screened for 11 genetic variants through polymerase chain reaction (PCR) techniques. Univariant followed by multivariant logistic regression analysis was applied to determine the genetic association.Results: Significant risk associations were observed for rs4532 and rs1799732 with MDD; and rs1006737 and rs2238056 with BD. However, after applying multiple test corrections rs4532 and rs1799732 association did not remain significant for MDD. Moreover, a protective association was found for three variants; DRD4-120bp, rs10033951 and rs2388334 in the current cohort.Conclusions: The present study revealed the risk association of single nucleotide polymorphisms (SNPs) rs1006737 and rs2238056 with BD and the protective effect of the DRD4-120bp variant in MDD and BD, of rs2388334 in BD and of rs10033951 in MDD, BD, and SHZ in the current Pakistani cohort. Thus, the study is valuable in understanding the genetic basis of MDD, BD and SHZ in the Pakistani population, which may pave the way for future functional studies.

Cholinergic-estrogen interaction is associated with the effect of education on attenuating cognitive sex differences in a Thai healthy population

The development of human brain is shaped by both genetic and environmental factors. Sex differences in cognitive function have been found in humans as a result of sexual dimorphism in neural information transmission. Numerous studies have reported the positive effects of education on cognitive functions. However, little work has investigated the effect of education on attenuating cognitive sex differences and the neural mechanisms behind it based on healthy population. In this study, the Wisconsin Card Sorting Test (WCST) was employed to examine sex differences in cognitive function in 135 Thai healthy subjects, and label-free quantitative proteomic method and bioinformatic analysis were used to study sex-specific neurotransmission-related protein expression profiles. The results showed sex differences in two WCST sub-scores: percentage of Total corrects and Total errors in the primary education group (Bayes factor>100) with males performed better, while such differences eliminated in secondary and tertiary education levels. Moreover, 11 differentially expressed proteins (DEPs) between men and women (FDR<0.1) were presented in both education groups, with majority of them upregulated in females. Half of those DEPs interacted directly with nAChR3, whereas the other DEPs were indirectly connected to the cholinergic pathways through interaction with estrogen. These findings provided a preliminary indication that a cholinergic-estrogen interaction relates to, and might underpin, the effect of education on attenuating cognitive sex differences in a Thai healthy population.

Striatal dopamine D2/3 receptors in medication-naïve schizophrenia: an [123I] IBZM SPECT study

BACKGROUND

The hyper-function of the striatal dopamine system has been suggested to underlie key pathophysiological mechanisms in schizophrenia. Moreover, patients have been observed to present a significant elevation of dopamine receptor availability compared to healthy controls. Although it is difficult to measure dopamine levels directly in humans, neurochemical imaging techniques such as single-photon emission computed tomography (SPECT) provide indirect indices of in vivo dopamine synthesis and release, and putative synaptic levels.

METHODS

We focused on the role of dopamine postsynaptic regulation using [¹²³I] iodobenzamide (IBZM) SPECT. We compared D_2/3 receptor availability between 53 healthy controls and 21 medication-naive patients with recent-onset schizophrenia.

RESULT

The mean specific striatal binding showed no significant difference between patients and controls (estimated difference = 0.001; 95% CI -0.11 to 0.11; F = 0.00, df = 1, 69; p = 0.99). There was a highly significant effect of age whereby IBZM binding declined with advancing age [estimated change per decade of age = -0.01(binding ratio); 95% CI -0.01 to -0.004; F = 11.5, df = 1, 69; p = 0.001]. No significant correlations were found between the mean specific striatal binding and psychopathological or cognitive rating scores.

CONCLUSIONS

Medication-naïve patients with recent-onset schizophrenia have similar D_2/3 receptor availability to healthy controls. We suggest that, rather than focusing exclusively on postsynaptic receptors, future treatments should target the presynaptic control of dopamine synthesis and release.

Dopamine D3 Receptor, Cognition and Cognitive Dysfunctions in Neuropsychiatric Disorders: From the Bench to the Bedside

The dopamine D3 receptor (D3R) plays a prominent role in the modulation of cognition in healthy individuals, as well as in the pathophysiological mechanism underlying the cognitive deficits affecting patients suffering from neuropsychiatric disorders. At a therapeutic level, a growing body of evidence suggests that the D3R blockade enhances cognitive and thus it may be an optimal therapeutic strategy against cognitive dysfunctions. However, this is not always the case because other ligands targeting the D3R, and behaving as partial agonists or biased agonists, may exert their pro-cognitive effect by maintaining adequate level of dopamine in key brain areas tuning cognitive performances. In this chapter, we review and discuss preclinical and clinical findings with the aim to remark the crucial role of the D3R in cognition and to strengthen the message that drugs targeting D3R may be excellent cognitive enhancers for the treatment of several neuropsychiatric and neurological disorders.

DNA Methylation and Schizophrenia: Current Literature and Future Perspective

Schizophrenia is a neuropsychiatric disorder characterized by dissociation of thoughts, idea, identity, and emotions. It has no central pathophysiological mechanism and precise diagnostic markers. Despite its high heritability, there are also environmental factors implicated in the development of schizophrenia. Epigenetic factors are thought to mediate the effects of environmental factors in the development of the disorder. Epigenetic modifications like DNA methylation are a risk factor for schizophrenia. Targeted gene approach studies attempted to find candidate gene methylation, but the results are contradictory. Genome-wide methylation studies are insufficient in literature and the available data do not cover different populations like the African populations. The current genome-wide studies have limitations related to the sample and methods used. Studies are required to control for these limitations. Integration of DNA methylation, gene expression, and their effects are important in the understanding of the development of schizophrenia and search for biomarkers. There are currently no precise and functional biomarkers for the disorder. Several epigenetic markers have been reported to be common in functional and peripheral tissue. This makes the peripheral tissue epigenetic changes a surrogate of functional tissue, suggesting common epigenetic alteration can be used as biomarkers of schizophrenia in peripheral tissue.

A Bayesian brain model of adaptive behavior: an application to the Wisconsin Card Sorting Task

Adaptive behavior emerges through a dynamic interaction between cognitive agents and changing environmental demands. The investigation of information processing underlying adaptive behavior relies on controlled experimental settings in which individuals are asked to accomplish demanding tasks whereby a hidden regularity or an abstract rule has to be learned dynamically. Although performance in such tasks is considered as a proxy for measuring high-level cognitive processes, the standard approach consists in summarizing observed response patterns by simple heuristic scoring measures. With this work, we propose and validate a new computational Bayesian model accounting for individual performance in the Wisconsin Card Sorting Test (WCST), a renowned clinical tool to measure set-shifting and deficient inhibitory processes on the basis of environmental feedback. We formalize the interaction between the task's structure, the received feedback, and the agent's behavior by building a model of the information processing mechanisms used to infer the hidden rules of the task environment. Furthermore, we embed the new model within the mathematical framework of the Bayesian Brain Theory (BBT), according to which beliefs about hidden environmental states are dynamically updated following the logic of Bayesian inference. Our computational model maps distinct cognitive processes into separable, neurobiologically plausible, information-theoretic constructs underlying observed response patterns. We assess model identification and expressiveness in accounting for meaningful human performance through extensive simulation studies. We then validate the model on real behavioral data in order to highlight the utility of the proposed model in recovering cognitive dynamics at an individual level. We highlight the potentials of our model in decomposing adaptive behavior in the WCST into several information-theoretic metrics revealing the trial-by-trial unfolding of information processing by focusing on two exemplary individuals whose behavior is examined in depth. Finally, we focus on the theoretical implications of our computational model by discussing the mapping between BBT constructs and functional neuroanatomical correlates of task performance. We further discuss the empirical benefit of recovering the assumed dynamics of information processing for both clinical and research practices, such as neurological assessment and model-based neuroscience.

Sleep Spindle-dependent Functional Connectivity Correlates with Cognitive Abilities

EEG studies have shown that interindividual differences in the electrophysiological properties of sleep spindles (e.g., density, amplitude, duration) are highly correlated with trait-like "reasoning" abilities (i.e., "fluid intelligence"; problem-solving skills; the ability to employ logic or identify complex patterns), but not interindividual differences in STM or "verbal" intellectual abilities. Previous simultaneous EEG-fMRI studies revealed brain activations time-locked to spindles. Our group has recently demonstrated that the extent of activation in a subset of these regions was related to interindividual differences in reasoning intellectual abilities, specifically. However, spindles reflect communication between spatially distant and functionally distinct brain areas. The functional communication among brain regions related to spindles and their relationship to reasoning abilities have yet to be investigated. Using simultaneous EEG-fMRI sleep recordings and psychophysiological interaction analysis, we identified spindle-related functional communication among brain regions in the thalamo-cortical-BG system, the salience network, and the default mode network. Furthermore, the extent of the functional connectivity of the cortical-striatal circuitry and the thalamo-cortical circuitry was specifically related to reasoning abilities but was unrelated to STM or verbal abilities, thus suggesting that individuals with higher fluid intelligence have stronger functional coupling among these brain areas during spontaneous spindle events. This may serve as a first step in further understanding the function of sleep spindles and the brain network functional communication, which support the capacity for fluid intelligence.

Association study of the functional Catechol-O-Methyltranferase (COMT) Val158Met polymorphism on executive cognitive function in a Thai sample

Catechol-O-Methyltranferase (COMT) plays a crucial role in the removal of cortical dopamine and is strongly implicated in human executive function. Numerous studies have reported associations of the COMT Val158Met (rs4680) polymorphism with executive function in healthy subjects. However, little work has investigated this in the Thai population and the relationship of age and education with this association remains unclear. Therefore, this study was designed to investigate the association of this polymorphism of the COMT gene with executive cognitive brain function in healthy subjects and the relationship with age and education. The Wisconsin Card Sorting Test (WCST) was performed to assess executive function in 254 healthy Thai subjects (aged 20-72 years). The results showed a significant association of rs4680 with executive function, in which Val/Met heterozygotes demonstrated better cognitive set shifting performance. Moreover, Met allele carriers showed a significantly stronger effect in the categories completed score than did Val homozygotes. Furthermore, age and education also showed a significant association with COMT genotype and WCST. These results revealed that executive cognitive function is associated with COMT genotype and influenced by age and/or education level in a Thai sample.

Personalized learning: From neurogenetics of behaviors to designing optimal language training

Variability in drug responsivity has prompted the development of Personalized Medicine, which has shown great promise in utilizing genotypic information to develop safer and more effective drug regimens for patients. Similarly, individual variability in learning outcomes has puzzled researchers who seek to create optimal learning environments for students. "Personalized Learning" seeks to identify genetic, neural and behavioral predictors of individual differences in learning and aims to use predictors to help create optimal teaching paradigms. Evidence for Personalized Learning can be observed by connecting research in pharmacogenomics, cognitive genetics and behavioral experiments across domains of learning, which provides a framework for conducting empirical studies from the laboratory to the classroom and holds promise for addressing learning effectiveness in the individual learners. Evidence can also be seen in the subdomain of speech learning, thus providing initial support for the applicability of Personalized Learning to language.

Dopamine D1 receptor (DRD1) 5' region haplotypes significantly affect transcriptional activity in vitro

The role of dopamine D1 receptor (DRD1) gene promoter polymorphisms in schizophrenia remains controversial. We aimed to characterize the polymorphisms in the promoter region because little is known about the extent of variance in this region and potential roles in gene transcription activity. In a previous case-control study, we amplified and genotyped the polymorphisms of DRD1 gene. According to its haplotype estimation, we identified eight SNPs and confirmed ten different haplotypes by cloning and sequencing the fragment spanning -1990 to +10. The promoter activity of these haplotypes was analyzed using dual luciferase assays in SH-SY5Y and HEK293 cells. Compared with the reference haplotype, the constructed haplotypes containing different variation sites could significantly alter the luciferase activity. Additionally, the prediction of the transcription factor binding sites was performed. Our examination could provide the informative reference for the role of DRD1 gene promoter in schizophrenia.

Association study of dopamine receptor genes polymorphism with cognitive functions in bipolar I disorder patients

OBJECTIVE

To determine the correlation among the polymorphisms of dopamine receptor genes, cognitive function of Bipolar disorder (BD) patients, and BD.

METHODS

Twenty-three Single Nucleotide Polymorphisms (SNPs) of dopamine receptor genes were genotyped using Illumina GoldenGate genotyping assay in 375 patients with bipolar I disorder (BD-I) (patients group) and 475 healthy controls (control group). Cognitive function tests were performed in 158 patients who were clinically stable and 307 healthy controls who were matched with the patients in age, sex, and education.

RESULTS

The allele frequencies of rs3758653 in the promoter region of the DRD4 gene were significantly different between patients group and control group (χ(2)=9.386, Corrected P=0.046). This significant difference was also observed between BD-I patients with psychotic symptoms and healthy controls (χ(2)=9.27, Corrected P=0.049). Patients with BD-I performed significantly worse than healthy controls in all cognitive domains (p<0.01) except TMTA errors and illegal time. Significant interactions between polymorphisms of rs5326 in DRD1 gene and phenotype (affected or unaffected with BD-I) were found in non-perseverative errors (β=3.20 and Corrected P=0.0034) on the Wisconsin Card Sorting Test (WCST). The allele of this SNP denoted the positive effect on the WCST non-perseverative errors in BD-I patients group (β=2.80 and Corrected P=0.017). The genotypic association analyses also supported the findings (F=4.24 and P=0.007), but this effect was not found in controls.

LIMITATIONS

The sample size was relatively small and the SNP coverage was limited, making it very important to be cautious when drawing a conclusion.

CONCLUSIONS

DRD4 gene may play an important role in psychotic symptomatology rather than in unique diagnosis, BD, for example. A genetic association exists between DRD1 gene and impaired cognition in BD.

Analysis of extinction acquisition to attenuated tones in prenatally stressed and non-stressed offspring following auditory fear conditioning

Stimulus generalization occurs when stimuli with characteristics similar to a previously conditioned stimulus (CS) become able to evoke a previously conditioned response. Experimental data (Lissek et al., 2005) indicate that patients with post-traumatic stress disorder (PTSD), more often show stimulus generalization following fear conditioning when tested under laboratory conditions. Factors surrounding this observation may contribute to two common features of PTSD: 1) hyper-responsiveness to sensory stimuli reminiscent of those associated with the original trauma, and 2) resistance of PTSD to extinction-based therapies. Adverse early experience is considered a risk factor for the later development of PTSD and in the present experiments we hypothesized that stimulus generalization would occur in an animal model of adverse early experience, the prenatally stressed (PS) rat. Adult PS and control (CON) rats underwent extensive pre-habituation to a conditioning chamber followed by conventional auditory fear conditioning. The next day both groups began an extinction regimen where a series of quieter (attenuated), CSs were administered prior to the full 75 dB training CS. When tested in this manner, PS rats froze at significantly lower tone amplitudes than did CON offspring on the first day of extinction training. This suggests that the PS rats had stimulus-generalized the CS to lower decibel tones. In addition to this finding, we also observed that PS rats froze more often and longer during three ensuing days of extinction training to attenuated tones. Group differences vanished when PS and CON rats were extinguished under conventional conditions. Thus, it appears that the two extinction regimens differed in their aversive cue saliency for the PS vs. CON rats. Follow-up prefrontal cortex transcriptome probing suggests that cholinergic and dopaminergic alterations may be involved.

Gene-sex interactions in schizophrenia: focus on dopamine neurotransmission

Schizophrenia is a severe mental disorder, with a highly complex and heterogenous clinical presentation. Our current perspectives posit that the pathogenic mechanisms of this illness lie in complex arrays of gene × environment interactions. Furthermore, several findings indicate that males have a higher susceptibility for schizophrenia, with earlier age of onset and overall poorer clinical prognosis. Based on these premises, several authors have recently begun exploring the possibility that the greater schizophrenia vulnerability in males may reflect specific gene × sex (G×S) interactions. Our knowledge on such G×S interactions in schizophrenia is still rudimentary; nevertheless, the bulk of preclinical evidence suggests that the molecular mechanisms for such interactions are likely contributed by the neurobiological effects of sex steroids on dopamine (DA) neurotransmission. Accordingly, several recent studies suggest a gender-specific association of certain DAergic genes with schizophrenia. These G×S interactions have been particularly documented for catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), the main enzymes catalyzing DA metabolism. In the present review, we will outline the current evidence on the interactions of DA-related genes and sex-related factors, and discuss the potential molecular substrates that may mediate their cooperative actions in schizophrenia pathogenesis.

Influences of COMT and 5-HTTLPR polymorphisms on cognitive flexibility in healthy women: inhibition of prepotent responses and memory updating

Understanding genetic factors that affect monoamine neurotransmitters flux in prefrontal cortex may help to further specify the complex neurobiological processes that underlie cognitive function and dysfunction in health and illness. The current study examined the associations between the polymorphisms of dopaminergic (COMT Met158Val) and serotoninergic (5-HTTLPR) genes and the sequential pattern of responses in a motor random generation task providing well-established indexes for executive functioning in a large sample of 255 healthy women. Participants homozygous for the Met allele of the COMT polymorphism showed impaired inhibition of prepotent responses, whereas individuals homozygous for the s-allele of the 5-HTTLPR showed a restricted ability to update information in working memory. Taken together the results indicate differentiated influences of dopaminergic and serotonergic genes on important and definite executive sub-processes related to cognitive flexibility.

Association of dopamine D1 receptor gene polymorphism with schizophrenia: a meta-analysis

To date, the role of dopamine D1 receptor (DRD1) polymorphism in schizophrenia remains controversial. We carried out a meta-analysis to determine whether DRD1 polymorphism influences the risk of schizophrenia. We examined whether rs4532 and rs5326 genetic variants are related to the etiology of schizophrenia, using a meta-analysis. Relevant case-control studies were retrieved by database searching and selected according to established inclusion criteria. A total of ten studies were identified and included in our meta-analysis, nine for rs4532, with 1,941 cases and 2,480 controls, and four for rs5326, with 1,285 cases and 1,195 controls. No significant association was found between the rs4532 locus and schizophrenia. For the rs5326 locus, the guanine-adenine (GA) genotype was associated with schizophrenia as a risk factor (for GA vs guanine-guanine [GG], odds ratio [OR] =1.36, 95% confidence interval [CI]: 1.15-1.61, P<0.001). The GA genotype of rs5326 increased the risk of schizophrenia, but there was no association between rs4532 and schizophrenia. These data may provide references for case-control studies in schizophrenia in future.

Carriers of the COMT Met/Met allele have higher degrees of hypnotizability, provided that they have good attentional control: a case of gene-trait interaction

Genetic factors may explain part of the interindividual variability in hypnotizability. A new avenue that may provide more comprehensive understanding of the phenotypic effects of genetic variations is the study of gene-trait interaction. In this study, the authors investigate the relationship of the dopamine-related COMT and the serotonin-related 5-HTTLPR polymorphisms to hypnotizability by taking individual differences in executive attention into account. Homozygosity for the COMT Met allele, putatively linked to the capability or proneness to dissociate from reality, was associated with high hypnotizability only if paired with high-attention ability. The finding can be integrated into hypnosis theory and represents a case of gene-trait interaction suggesting that investigating the effects of a gene in the context of relevant psychological traits may further elucidate gene-brain-behavior relationships.

The potential role of dopamine D₃ receptor neurotransmission in cognition

Currently available treatments have limited pro-cognitive effects for neuropsychiatric disorders, such as schizophrenia, Parkinson's disease and Alzheimer's disease. The primary objective of this work is to review the literature on the role of dopamine D₃ receptors in cognition, and propose dopamine D₃ receptor antagonists as possible cognitive enhancers for neuropsychiatric disorders. A literature search was performed to identify animal and human studies on D₃ receptors and cognition using PubMed, MEDLINE and EMBASE. The search terms included "dopamine D₃ receptor" and "cognition". The literature search identified 164 articles. The results revealed: (1) D₃ receptors are associated with cognitive functioning in both healthy individuals and those with neuropsychiatric disorders; (2) D₃ receptor blockade appears to enhance while D₃ receptor agonism seems to impair cognitive function, including memory, attention, learning, processing speed, social recognition and executive function independent of age; and (3) D₃ receptor antagonists may exert their pro-cognitive effect by enhancing the release of acetylcholine in the prefrontal cortex, disinhibiting the activity of dopamine neurons projecting to the nucleus accumbens or prefrontal cortex, or activating CREB signaling in the hippocampus. These findings suggest that D₃ receptor blockade may enhance cognitive performance in healthy individuals and treat cognitive dysfunction in individuals with a neuropsychiatric disorder. Clinical trials are needed to confirm these effects.

NR4A2: effects of an "orphan" receptor on sustained attention in a schizophrenic population

NR4A2 (nuclear receptor subfamily 4 group A member 2) or Nurr1 is a transcription factor implied in the differentiation, maturation, and survival of dopaminergic neurons. It also has a role in the expression of several proteins that are necessary for the synthesis and regulation of dopamine (DA), such as tyrosine hidroxilase, dopamine transporter, vesicular monoamine transporter 2, and cRET. DA is an important neurotransmitter in attentional pathways. Our aim was to evaluate the influence of NR4A2 gene in the performance of schizophrenia (SZ) patients and healthy subjects on a sustained attention task. For this study, we collected 188 SZ subjects (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) and 100 control individuals. We genotyped 5 tag SNPs in NR4A2 gene: rs1150143 (C/G), rs1150144 (A/G), rs834830 (A/G), rs1466408 (T/A), and rs707132 (A/G). We also analyzed the influence of its haplotypes (frequency>5%). To examine sustained attention, all the individuals completed the Degraded Stimulus Continuous Performance Test. We evaluated "hits," "reaction time," "sensibility a," and "false alarms." In the schizophrenic group, recessive genotypes of rs1150143, rs1150144, rs834830, and rs707132 were associated with a worse performance. SZ subjects who carried GGGTG haplotype showed less hits (P<.004), lower sensibility a scores (P<.009), and a higher reaction time (P=.013). We observed a sex effect of the gene: genotype and haplotype associations were only present in the male group. We conclude that NR4A2 gene is involved in attentional deficits of SZ patients, modifying hits, sensibility a, and reaction time.

Toxoplasma gondii infection, from predation to schizophrenia: can animal behaviour help us understand human behaviour?

We examine the role of the protozoan Toxoplasma gondii as a manipulatory parasite and question what role study of infections in its natural intermediate rodent hosts and other secondary hosts, including humans, may elucidate in terms of the epidemiology, evolution and clinical applications of infection. In particular, we focus on the potential association between T. gondii and schizophrenia. We introduce the novel term 'T. gondii-rat manipulation-schizophrenia model' and propose how future behavioural research on this model should be performed from a biological, clinical and ethically appropriate perspective.

Combination training in aging individuals modifies functional connectivity and cognition, and is potentially affected by dopamine-related genes

Background

Aging is a major co-risk factor in many neurodegenerative diseases. Cognitive enrichment positively affects the structural plasticity of the aging brain. In this study, we evaluated effects of a set of structured multimodal activities (Combination Training; CT) on cognitive performances, functional connectivity, and cortical thickness of a group of healthy elderly individuals. CT lasted six months.

Methodology

Neuropsychological and occupational performances were evaluated before and at the end of the training period. fMRI was used to assess effects of training on resting state network (RSN) functional connectivity using Independent Component Analysis (ICA). Effects on cortical thickness were also studied. Finally, we evaluated whether specific dopamine-related genes can affect the response to training.

Principal Findings

Results of the study indicate that CT improves cognitive/occupational performances and reorganizes functional connectivity. Intriguingly, individuals responding to CT showed specific dopamine-related genotypes. Indeed, analysis of dopamine-related genes revealed that carriers of DRD3 ser9gly and COMT Val158Met polymorphisms had the greatest benefits from exposure to CT.

Conclusions and Significance

Overall, our findings support the idea that exposure to a set of structured multimodal activities can be an effective strategy to counteract aging-related cognitive decline and also indicate that significant capability of functional and structural changes are maintained in the elderly.

Association between BDNF Val66Met polymorphism and cognitive performance in antipsychotic-naïve patients with schizophrenia

Cognitive impairment is one of the core symptoms in schizophrenia, which reflects the neurodevelopmental deficits in the etiology of this disease. Brain-derived neurotrophic factor (BDNF) plays an important role in various neurodevelopmental processes. Growing evidence has shown that BDNF may be involved in the etiology of schizophrenia. The aim of this study was to examine the association of the BDNF Val66Met polymorphism with cognition in patients with schizophrenia. Various neuropsychological tests including the Wechsler Adult Intelligence Scale-Revised, the Wechsler Memory Scale-Revised, and the Wisconsin Card Sorting Test (WCST) were employed in a sample of 112 antipsychotic-naïve patients with schizophrenia and 63 healthy controls. We examined the Val66Met polymorphism in the 112 patients and 394 controls. Among the patients, cognition was compared between Met allele carriers and non-Met allele carriers. A wide range of cognitive deficits were demonstrated in the schizophrenic patients, compared with the controls (Ps < 0.01). No significant differences of genotype or allele distribution were identified between patients and controls. The patients with Met allele showed more percent WCST perseverative errors than those without Met allele (P = 0.007). After stratification based on gender, an association between the Met allele and a higher percentage of perseverative errors was found in male patients (P = 0.014), but not in females (P = 0.09). Cognitive performance is broadly impaired in schizophrenic patients. The BDNF Val66Met polymorphism may be involved in the impaired executive function. This effect may have gender-specific characteristics.

Linking neurogenetics and individual differences in language learning: the dopamine hypothesis

Fundamental advances in neuroscience have come from investigations into neuroplasticity and learning. These investigations often focus on identifying universal principles across different individuals of the same species. Increasingly, individual differences in learning success have also been observed, such that any seemingly universal principle might only be applicable to a certain extent within a particular learner. One potential source of this variation is individuals' genetic differences. Adult language learning provides a unique opportunity for understanding individual differences and genetic bases of neuroplasticity because of the large individual differences in learning success that have already been documented, and because of the body of empirical work connecting language learning and neurocognition. In this article, we review the literature on the genetic bases of neurocognition, especially studies examining polymorphisms of dopamine (DA)-related genes and procedural learning. This review leads us to hypothesize that there may be an association between DA-related genetic variation and language learning differences. If this hypothesis is supported by future empirical findings we suggest that it may point to neurogenetic markers that allow for language learning to be personalized.

An association study between dopamine D1 receptor gene polymorphisms and the risk of schizophrenia

Deficits in dopamine transmission at D1 receptors in the PFC are implicated in schizophrenia. Genetic polymorphisms in functional regions of DRD1 have a plausible role in modulating the risk of schizophrenia. In order to evaluate the role of DRD1 polymorphisms as a risk factor for schizophrenia, we performed a detailed analysis of possible functional single nucleotide polymorphisms (SNPs) in regulatory and coding regions of DRD1. Nine SNPs were identified by DNA sequencing in 20 patients with schizophrenia. Then 385 cases and 350 healthy control subjects were genotyped using the nine SNPs (rs4867798, rs686, rs1799914, rs4532 rs5326, rs265981, rs10078714, rs10063995, rs10078866). Statistically significant differences were observed in the allelic or genotypic frequencies of the rs686 and rs10063995 polymorphism in the DRD1 gene. A significantly lower risk of schizophrenia was associated with the G allele and AG+GG genotype of rs686 (OR (G allele)=0.632, 95%CI (G allele): 0.470-0.849; OR (AG+GG genotype)=0.578, 95%CI (AG+GG genotype): 0.416-0.803) compared with the A allele and AA genotype, respectively. And a significantly increased risk of schizophrenia was associated with the T allele of rs10063995 (OR=1.446, 95%CI: 1.125-1.859) compared with the G allele. The haplotype analysis indicated the G-T variant containing the T allele of rs10063995 is a risk for schizophrenia (P=0.005, OR=1.467, 95%CI: 1.123-1.917). These data suggest that DRD1 gene polymorphisms confer susceptibility to schizophrenia, and also support the notion that dysfunction of DRD1 is involved in the pathophysiological process of schizophrenia.

Associations between DRDs and schizophrenia in a Korean population: multi-stage association analyses

The dysregulation of the dopaminergic system has been implicated in the pathophysiology of major psychosis, including schizophrenia, with dopamine receptor genes (DRDs) presently targeted as the most promising candidate genes. We investigated DRD1-5 for association with schizophrenia using a multi-stage approach in a Korean sample. One hundred forty-two SNPs in DRD1-5 were selected from the dbSNP, and the associations of each SNP were then screened and typed by MALDI-TOF mass spectrometry using pooled DNA samples from 150 patients with major psychosis and 150 controls. Each of the suggested SNPs was then genotyped and tested for an association within the individual samples comprising each pool. Finally, the positively associated SNPs were genotyped in an extended sample of 270 patients with schizophrenia and 350 controls. Among the 142 SNPs, 88 (62%) SNPs in our Korean population were polymorphic. At the pooling stage, 10 SNPs (DRD1: 2, DRD2: 3, and DRD4: 5) were identified (P<0.05). SNPs rs1799914 of DRD1 (P=0.046) and rs752306 of DRD4 (P=0.017) had significantly different allele frequencies in the individually genotyped samples comprising the pool. In the final stage, with the extended sample, the suggestive association of DRD4 with rs752306 was lost, but the association of DRD1 with rs1799914 gained greater significance (P=0.017). In these large-scale multi-stage analyses, we were able to find a possible association between DRD1 and schizophrenia. These findings suggested the potential contribution of a multi-step strategy for finding genes related to schizophrenia.

Pharmacogenomic implications of variants of monoaminergic-related genes in geriatric psychiatry

Response to psychiatric medications in later life is highly heterogeneous and complex. Monoaminergic-related polymorphisms may influence medication response and susceptibility to side effects in elderly individuals. Individuals with the lower function short (S) allele of the serotonin transporter gene (SLC6A4) insertion/deletion (indel) promoter polymorphism (5-HTTLPR) have both increased the likelihood of adverse drug events and increased the need for higher antidepressant concentrations to obtain maximum antidepressant response. By contrast, carriers of the higher expression homozygous long allele (L/L) genotype may respond at lower concentrations. The differential role of these polymorphisms appears at early stages of treatment rather than in the final antidepressant outcome. Research findings suggest that the rs25531 SNP may influence functional expression of the L allele. Similarly, a variable number of tandem repeats in the second intron of the serotonin transporter gene may influence the expression of SLC6A4 and the implications of these variants may be influenced by aging. Two polymorphisms, rs2242466 (-182T/C) and rs5569 (1287G/A), in the norepinephrine transporter gene (SLC6A2 or NET) have been associated with antidepressant response. Studies in dopamine-related polymorphisms have focused on associations with neuroleptic-induced movement disorders. The rs1800497 variant (Taq1A) of the dopamine receptor D2 (DRD2) gene located in a noncoding 3´ region may regulate expression of D2 receptors. The rs6280 variant (Ser9Gly) of the dopamine receptor 3 (DRD3) gene may influence the binding affinity of D3 receptors as a result of serine to glycine substitution of the receptor protein. A multicenter collaborative research effort would be an effective strategy to increase sample sizes to further investigate how gene variants impact the pharmacodynamics and pharmacokinetics of psychotropic drugs in elderly persons.

Sexually dimorphic interaction between the DRD1 and COMT genes in schizophrenia

Dopaminergic dysfunction in the prefrontal cortex (PFC) is involved in the pathophysiology of schizophrenia. In the PFC, dopamine signalling largely depends on the D1 receptors, which are coded by the DRD1 gene, and on the regulation of dopamine levels by the enzyme catechol-O-methyltransferase (COMT). Here, we investigate the role of DRD1 and its interaction with the COMT gene in schizophrenic patients. In two gender-limited independent patient and control samples, we genotype five Tag single nucleotide polymorphisms (tagSNPs) of DRD1. The DRD1 SNP and haplotype associations, as well as interaction effects with the Val158Met COMT SNP were analyzed. In the male sample, we found the rs11746641 and rs11749676 DRD1 SNPs were associated with schizophrenia. Haplotype analyses identified the T-A-T-C-T variant related to a protective effect (P = 0.008) and the G-G-T-C-C variant that showed a tendency to be a risk factor for the disorder (P = 0.012). A logistic regression analysis revealed a significant pattern of interaction between DRD1 and COMT for both the rs11746641 (P = 0.002) and rs11749676 (P = 4.5 x 10(-5)) SNPs. DRD1-associated haplotypes were exclusively related to schizophrenia in the Val homozygous subgroup of patients (T-A-T-C-T: P = 0.003; G-G-T-C-C: P = 0.006). In females, none of the DRD1 SNPs were linked to the disorder. Our genetic data suggest that DRD1 and COMT are epistatically associated with protection against and the risk of developing schizophrenia in a gender-dependent fashion, and support the role of dopamine dysfunction at the PFC in the pathophysiology of this disorder.

No genetic association between dopamine D1 receptor gene and [early onset] schizophrenia

Decreased dopaminergic activity in the prefrontal cortex (PFC) has been consistently reported in schizophrenia patients. The dopamine D1 receptor (DRD1) plays an important role in mediating dopaminergic transmission in the PFC. Controversy about this topic still exists despite ample evidence suggesting that the DRD1 gene is associated with performance on neuropsychological tests probing the function of the PFC in schizophrenia, as well as positive and negative symptoms and therapeutic response to antipsychotics. To determine whether this gene is involved in the etiology of schizophrenia, we undertook a case-control study to look for an association. We genotyped five single nucleotide polymorphisms (SNPs) rs4532, rs5326, rs2168631, rs6882300 and rs267418 within the DRD1 involving 373 schizophrenia patients with early age of onset and 379 healthy subjects. No significant differences of genotype, allele or haplotype distribution were identified between patients and controls. Our results do not preclude a possible role of DRD1 in the etiology of schizophrenia. As an important dopaminergic gene, DRD1 may contribute to schizophrenia by interacting with other genes. Further relevant studies are warranted.

Longitudinal alterations of executive function in non-psychotic adolescents at familial risk for schizophrenia

Genetic diathesis to schizophrenia may involve alterations of adolescent neurodevelopment manifesting as cognitive deficits. Brain regions mediating executive function (fronto-striatal circuits) develop during adolescence while those supporting elementary aspects of attention (e.g. sustained focused attention) have a more protracted maturation beginning in childhood. We hence predicted that adolescents at risk for schizophrenia would show a failure of normal maturation of executive function. We prospectively assessed 18 offspring and 6 siblings of schizophrenia patients (HR) and 28 healthy controls at baseline, year-1 and year-2 follow-up using the Continuous Performance Test [visual-d'] and Wisconsin Card Sort Test (WCST). Perseverative errors on the WCST in HR remained stable but decreased in controls over the follow-up (study-group by assessment-time interaction, p=0.01, controlling for IQ). No significant study-group by assessment-time interactions were seen for sustained attentional performance. HR may not improve while healthy subjects progressively improve on executive function during adolescence and early adulthood. Our results suggest an altered maturational trajectory of executive function during adolescence in individuals at familial risk for schizophrenia.

Correlation between errors on the Wisconsin Card Sorting Test and the availability of striatal dopamine transporters in healthy volunteers

BACKGROUND

Although studies have indicated that the frontal lobe plays an important role in performance on the Wisconsin Card Sorting Test (WCST) and that basal ganglia play a specific role in frontal lobe function, the role of striatal dopamine (DA) activity in performance on the WCST remains unclear.

METHODS

We assessed the relation between the availability of striatal dopamine transporters (DATs) and performance on the WCST as a measure of executive function in healthy individuals. We approximated the availability of DATs in 53 healthy volunteers aged 19-61 years by use of single photon emission computed tomography with technetium-99m (99mTc)-TRODAT-1 as the ligand. The WCST was administered to all participants.

RESULTS

The availability of DAT was significantly negatively correlated with perseverative errors on the WCST, both before and after adjustment for body mass index (r(before) = -0.39, p = 0.004; r(after) = -0.39, p = 0.005).

LIMITATIONS

This was an association study; thus, a causal relation between DAT availability and performance cannot be confirmed.

CONCLUSION

Our results suggest that striatal DAT availability may play a role in executive function as measured by the WCST.

The dopamine D3 receptor (DRD3) gene and risk of schizophrenia: case-control studies and an updated meta-analysis

The dopamine D3 receptor (DRD3) has been suggested to be involved in the pathophysiology of schizophrenia. DRD3 has been tested for an association with schizophrenia, but with conflicting results. A recent meta-analysis suggested that the haplotype T-T-T-G for the SNPs rs7631540-rs1486012-rs2134655-rs963468 may confer protection against schizophrenia. However, almost all previous studies of the association between DRD3 and schizophrenia have been performed using a relatively small sample size and a limited number of markers. To assess whether DRD3 is implicated in vulnerability to schizophrenia, we conducted case-control association studies and performed an updated meta-analysis. In the first population (595 patients and 598 controls), we examined 16 genotyped single nucleotide polymorphisms (SNPs), including tagging SNPs selected from the HapMap database and SNPs detected through resequencing, as well as 58 imputed SNPs that are not directly genotyped. To confirm the results obtained, we genotyped the SNPs rs7631540-rs1486012-rs2134655-rs963468 in a second, independent population (2126 patients and 2228 controls). We also performed an updated meta-analysis of the haplotype, combining the results obtained in five populations, with a total sample size of 7551. No supportive evidence was obtained for an association between DRD3 and schizophrenia in our Japanese subjects. Our updated meta-analysis also failed to confirm the existence of a protective haplotype. To draw a definitive conclusion, further studies using larger samples and sufficient markers should be carried out in various ethnic populations.

Response to prophylactic lithium in bipolar disorder may be associated with a preservation of executive cognitive functions

We assessed performance on the Wisconsin Card Sorting Test (WCST), measuring executive functions, in 30 patients showing different prophylactic effect of lithium (excellent lithium responders-ER, partial responders-PR and non-responders-NR), and in fifty persons of their offspring (12 of ER, 26 of PR, and 12 of NR). Age- and gender head-to-head matched population consisted of 30 subjects for lithium group and 50 subjects for the offspring of lithium patients. In lithium patients, NR had significantly worse results compared to the remaining groups and to control subjects on perseverative errors (WCST-P) and conceptual responses (WCST-%conc). No differences were observed in the offspring of patients with different effect of lithium, however, they showed an impairment on WCST-P and WCST-%conc compared to matched healthy controls. Therefore, the favorable effect of lithium prophylaxis may be associated with a preservation of executive cognitive functions and the offspring of bipolar patients shows an impairment of such functions.

Cognitive flexibility is associated with KIBRA variant and modulated by recent tobacco use

The kidney and brain expressed protein gene (KIBRA) and the calsyntenin 2 gene (CLSTN2) are reportedly involved in synaptic plasticity. Single nucleotide polymorphisms (SNPs) rs17070145 (KIBRA) and rs6439886 (CLSTN2) have been found to affect memory performance measures. This study examined the association of KIBRA SNP rs17070145 and CLSTN2 SNPs rs6439886 and rs17348572 (a nonsynonymous variant) with cognitive flexibility in 674 African Americans (AAs; 526 current smokers) and 419 European Americans (EAs; 318 current smokers). The subjects' cognitive flexibility was assessed using the Wisconsin Card Sorting Test. The effects on cognitive flexibility of sex, age, education, and tobacco recency (a possible mediator of gene effects in smokers), the three SNPs, and the interaction of each SNP with tobacco recency were analyzed using multivariate analysis of variance. In AAs, there were no main or interaction effects of the SNPs on cognitive flexibility. In EAs, the two CLSTN2 SNPs showed no main effect on cognitive flexibility. However, among EAs, individuals with the KIBRA rs17070145 T allele made significantly more perseverative responses (P=0.002) and perseverative errors (P=0.002) than those with no T allele. Furthermore, among EAs with the rs17070145 T allele, current smokers made significantly fewer perseverative responses (P<0.001) and perseverative errors (P<0.001) than past smokers. Nongenetic factors (age, education, and tobacco recency) had substantial effects on cognitive flexibility in both AAs and EAs. We conclude that variation in KIBRA influences cognitive flexibility in a population-specific way, and that current smoking status moderates this effect.

A genome-wide study of common SNPs and CNVs in cognitive performance in the CANTAB

Psychiatric disorders such as schizophrenia are commonly accompanied by cognitive impairments that are treatment resistant and crucial to functional outcome. There has been great interest in studying cognitive measures as endophenotypes for psychiatric disorders, with the hope that their genetic basis will be clearer. To investigate this, we performed a genome-wide association study involving 11 cognitive phenotypes from the Cambridge Neuropsychological Test Automated Battery. We showed these measures to be heritable by comparing the correlation in 100 monozygotic and 100 dizygotic twin pairs. The full battery was tested in approximately 750 subjects, and for spatial and verbal recognition memory, we investigated a further 500 individuals to search for smaller genetic effects. We were unable to find any genome-wide significant associations with either SNPs or common copy number variants. Nor could we formally replicate any polymorphism that has been previously associated with cognition, although we found a weak signal of lower than expected P-values for variants in a set of 10 candidate genes. We additionally investigated SNPs in genomic loci that have been shown to harbor rare variants that associate with neuropsychiatric disorders, to see if they showed any suggestion of association when considered as a separate set. Only NRXN1 showed evidence of significant association with cognition. These results suggest that common genetic variation does not strongly influence cognition in healthy subjects and that cognitive measures do not represent a more tractable genetic trait than clinical endpoints such as schizophrenia. We discuss a possible role for rare variation in cognitive genomics.

Novel Mutation Detection of Regulatory Molecule Dopamine Gene Receptors (D1–D5) Encoding Analysis on Human Peripheral Blood Lymphocytes in Schizophrenia Patients

There is much evidence which highlights the involvement of the dopamine system in the pathophysiology of schizophrenia. Recently, there have been reports of detected mutations in dopamine gene receptors in genomic DNA of schizophrenia. In this study, we attempt to determine whether there is mutation in encoding dopamine receptor. The PBMC was separated from whole blood by Ficoll-hypaque; the total cellular RNA was extracted and the cDNA was synthesized. This process followed by real-time PCR using primer pairs specific for five dopamine receptor mRNAs and β-actin as internal control. The results show the presence of all types of dopamine receptor types in lymphocytes. The mutational analysis of the obtained PCR products for the respective dopamine receptor fragments were analyzed by sequenced capillary system. The results presented in this study confirm the high frequency of mutations in dopamine gene receptor DRD5 in schizophrenia patients. Mutational amino acid changes in dopamine gene receptors of DR2, DR3, DR4 but not DR1 are also shown. In conclusion, this is the first report of such complete mutational analyses in all dopamine gene receptors. Moreover, we found new mutations and 80% frequency of mutations in DRD5. These data further strengthen the argument for the role of dopamine gene receptor mutations in the pathogenesis of schizophrenia.

Multivariate genomewide linkage scan of neurocognitive traits and ADHD symptoms: suggestive linkage to 3q13

Family and twin studies suggest that a range of neurocognitive traits index the inherited liability to ADHD; however, the utility of such measures as endophenotypes in molecular genetic studies remains largely untested. The current article examined whether the inclusion of neurocognitive measures in a genomewide linkage analysis of ADHD could aid in identifying QTL linked to the behavioral symptoms of the condition. Data were from an affected sibling pair linkage study of DSM-IV ADHD conducted at Massachusetts General Hospital. The sample included 1,212 individuals from 271 families. ADHD symptoms were assessed with the K-SADS-E. The neurocognitive battery included Wechsler Intelligence Scales subtests, the Stroop, the Wisconsin Card Sorting Test (WCST), the Rey-Osterreith Complex Figure, a working memory CPT, the CVLT and WRAT-III subscales. Evidence for linkage was assessed using a simulation-based method that combines information from univariate analyses into the equivalent of a multivariate test. After correction for multiple trait testing, a region on chromosome 3q13 showed suggestive linkage to all neurocognitive traits examined and inattention symptoms of ADHD. The second highest peak occurred on 22q12 but showed linkage to a single subscale of the WCST. In univariate analysis, this region retained criteria for suggestive linkage to this measure after correction for multiple trait testing. Our primary findings raise the possibility that one or more genes on 3q13 influence neurocognitive functions and behavioral symptoms of inattention. Overall, these data support the utility of neurocognitive traits as ADHD endophenotypes, but also highlight their limited genetic overlap with the disorder.

The Wisconsin Card Sorting impairment in schizophrenia is evident in the first four trials

BACKGROUND

Schizophrenia (SZ) patients' low scores on the Wisconsin Card Sorting Test (WCST) are often attributed to frequent perseverative errors, a pattern typically interpreted as a failure to shift from previously rewarded behavior in response to negative feedback. In this study we tested the hypothesis that SZ patients, due to dysregulated error-processing mechanisms, are more fundamentally impaired in their on-line, trial-to-trial use of feedback to guide behavior.

METHODS

Analysis of archival WCST data from 145 adults with schizophrenia and 80 healthy comparison subjects.

RESULTS

Schizophrenia patients' impaired use of negative feedback was evident on the first four WCST cards, where they were significantly less accurate than comparison subjects. Performance on these early cards significantly predicted overall task success as indexed by categories completed and proportion of perseverative errors.

CONCLUSIONS

Patients' poor performance on pre-shift WCST trials likely reflects a fundamental impairment in the ability to use feedback to guide behavior. Recent data from both humans and primates suggest that reward-based learning processes like those employed in the WCST are driven by phasic changes in midbrain dopamine activity. It might, therefore, be possible to interpret higher order executive dysfunction in schizophrenia as a manifestation of altered DA signaling.

DRD3, but not COMT or DRD2, genotype affects executive functions in healthy and first-episode psychosis adolescents

Catechol-O-methyltransferase (COMT) and dopamine receptors 2 (DRD2) and 3 (DRD3) have been associated with a higher risk of developing psychosis and with dopaminergic system (DAS) regulation. Frontal cognitive functioning has been proven to be a useful endophenotype for psychosis and it is partially controlled by the DAS. Val158Met (rs4680, COMT), Taq IA (rs1800497, DRD2) and Ser9Gly (rs6280; DRD3) polymorphisms were analyzed in a sample of 84 adolescent Caucasian patients with first-episode psychosis (ages 11-17) and 85 healthy Caucasian controls (ages 10-17). A comprehensive neuropsychological battery, assessing attention, working memory, memory, and executive functions, was administered to the entire sample. The relationship between neuropsychological scores and genotype was determined. Subjects with the DRD3 Gly/Gly genotype showed significantly poorer performance than Ser/Ser subjects in executive functioning tasks (P = 0.002; adjusted R(2) = 0.031), with no significant differences in the other cognitive paradigms. Neither COMT nor DRD2 polymorphisms significantly contributed to variance in cognition in our adolescent sample. The DRD3 Ser9Gly polymorphism seems to be involved with prefrontal cognition. This effect seems to be heterogeneous in terms of cognitive paradigms. The lack of association between COMT and DRD2 genotypes and cognition in our sample may be partially explained by the young age of the sample and the clinical heterogeneity of the patients.

Polymorphisms in dopamine receptor DRD1 and DRD2 genes and psychopathological and extrapyramidal symptoms in patients on long-term antipsychotic treatment

DRD(1) and DRD(2) receptor gene variants have been associated with clinical aspects of schizophrenia; however only specific features were analyzed in different samples. To assess the complex interaction between genetic and clinical factors, we studied the possible cross-interactions between DRD1 and DRD2 dopamine receptor gene polymorphisms, symptomatology of schizophrenia and schizoaffective disorders, and the occurrence of treatment induced side effects taking into consideration possible clinical confounding variables. One hundred thirty one outpatients in stable remission meeting the DSMIV criteria for schizophrenia spectrum disorders and receiving long-term maintenance therapy with haloperidol, fluphenazine, zuclopenthixole, or risperidone were genotyped for DRD1 A-48G, DRD2 Ins-141CDel, and DRD2 Ser311Cys polymorphisms. Psychopathological symptoms were assessed with the positive and negative syndrome scale for schizophrenia (PANSS). Extrapyramidal side effects were assessed with the Simpson-Angus extrapyramidal side effects scale (EPS), the Barnes Akathisia scale (BARS), and the abnormal involuntary movement scale (AIMS). Drug dosage was included as covariant because it was associated with the severity of symptomatology, akathisia, and parkinsonism. No association was observed for DRD1 and DRD2 polymorphisms and extrapyramidal side effects, or with the other clinical variables considered. Our study suggests that DRD1 and DRD2 variants are not liability factors for tardive dyskinesia.

Polymorphisms of the Fyn kinase gene and a performance on the Wisconsin Card Sorting Test in schizophrenia

The glutamatergic system has been implicated in the pathogenesis and prefrontal cortex dysfunctions in schizophrenia. The Src-family tyrosine kinase Fyn plays a key role in the interaction between brain-derived neurotrophic factor and glutamatergic receptor N-methyl-D-aspartate, in prefrontal cortex. We estimated an association between three polymorphisms of Fyn gene and performance on the Wisconsin Card Sorting Test, measuring prefrontal cortex functions, in 188 schizophrenic patients. Patients with T/T genotype of IVS10+T/C polymorphism and T/T genotype of Ex12+894T/G polymorphism made significantly less perseverative errors in the Wisconsin Card Sorting Test compared with patients with remaining genotypes, and obtained numerically better results in other Wisconsin Card Sorting Test domains. No significant differences in Wisconsin Card Sorting Test performance were found as to -93 A/G polymorphism. The main finding of the study is showing a relationship between polymorphisms of the Fyn gene, related to the function of glutamatergic system, and a performance on neuropsychological test of prefrontal cortex activity in schizophrenic patients.

Performance in the Wisconsin Card Sorting Test and the C957T polymorphism of the DRD2 gene in healthy volunteers

INTRODUCTION

Previous studies have associated a decreased striatal D2 dopamine receptor (DRD2) binding with impaired performance in cognitive tasks. In vivo studies have found a lower DRD2 binding associated with the CC genotype of the C957T single nucleotide polymorphism (SNP) of the DRD2 gene.

OBJECTIVE

The aim of this study was to investigate the relationship between executive functions and the C957T DRD2 SNP. We hypothesized that the CC genotype would be associated with a poorer executive functioning.

METHODS

Our sample consisted of 83 healthy volunteers (28 males and 55 females; mean age 25.2, SD 1.7 years). To assess executive functions, the Wisconsin Card Sorting Test was used, considering the variables perseverative errors, perseverative responses, and number of categories achieved. The genotype distribution was 13 CC, 41 CT, and 29 TT, satisfying Hardy-Weinberg equilibrium.

RESULTS

Carriers of the CC genotype, compared with carriers of the CT/TT genotypes, achieved significantly fewer categories (5.00 vs. 5.81; p = 0.004), made a greater number of perseverative errors (13.46 vs. 8.39; p = 0.018), and had a greater number of perseverative responses (14.92 vs. 8.94; p = 0.014).

CONCLUSIONS

Our results support the hypothesis that the C957T DRD2 SNP may influence cognitive performance through its repercussions on central dopaminergic function.

Towards understanding the schizophrenia code: an expanded convergent functional genomics approach

Identifying genes for schizophrenia through classical genetic approaches has proven arduous. Here, we present a comprehensive convergent analysis that translationally integrates brain gene expression data from a relevant pharmacogenomic mouse model (involving treatments with a psychomimetic agent - phencyclidine (PCP), and an anti-psychotic - clozapine), with human genetic linkage data and human postmortem brain data, as a Bayesian strategy of cross validating findings. Topping the list of candidate genes, we have three genes involved in GABA neurotransmission (GABRA1, GABBR1, and GAD2), one gene involved in glutamate neurotransmission (GRIA2), one gene involved in neuropeptide signaling (TAC1), two genes involved in synaptic function (SYN2 and KCNJ4), six genes involved in myelin/glial function (CNP, MAL, MBP, PLP1, MOBP and GFAP), and one gene involved in lipid metabolism (LPL). These data suggest that schizophrenia is primarily a disorder of brain functional and structural connectivity, with GABA neurotransmission playing a prominent role. These findings may explain the EEG gamma band abnormalities detected in schizophrenia. The analysis also revealed other high probability candidates genes (neurotransmitter signaling, other structural proteins, ion channels, signal transduction, regulatory enzymes, neuronal migration/neurite outgrowth, clock genes, transcription factors, RNA regulatory genes), pathways and mechanisms of likely importance in pathophysiology. Some of the pathways identified suggest possible avenues for augmentation pharmacotherapy of schizophrenia with other existing agents, such as benzodiazepines, anticonvulsants and lipid modulating agents. Other pathways are new potential targets for drug development. Lastly, a comparison with our earlier work on bipolar disorder illuminates the significant molecular overlap between schizophrenia and bipolar disorder.

Boolean network analysis of a neurotransmitter signaling pathway

BACKGROUND

A Boolean network is a simple computational model that may provide insight into the overall behavior of genetic networks and is represented by variables with two possible states (on/off), of the individual nodes/genes of the network. In this study, a Boolean network model has been used to simulate a molecular pathway between two neurotransmitter receptor, dopamine and glutamate receptor, systems in order to understand the consequence of using logic gate rules between nodes, which have two possible states (active and inactive).

RESULTS

The dynamical properties of this Boolean network model of the biochemical pathway shows that, the pathway is stable and that, deletion/knockout of certain biologically important nodes cause significant perturbation to this network. The analysis clearly shows that in addition to the expected components dopamine and dopamine receptor 2 (DRD2), Ca(2+) ions play a critical role in maintaining stability of the pathway.

CONCLUSION

So this method may be useful for the identification of potential genetic targets, whose loss of function in biochemical pathways may be responsible for disease onset. The molecular pathway considered in this study has been implicated with a complex disorder like schizophrenia, which has a complex multifactorial etiology.

Dopamine receptor D1 gene -48A/G polymorphism is associated with bipolar illness but not with schizophrenia in a Polish population

Dysregulation of dopaminergic neurotransmission has been implicated in the etiology of major psychoses. The dopamine D(1) receptor (DRD1) plays a role in some brain functions and mechanisms of psychotropic drugs. Therefore, the DRD1 gene makes a good candidate gene for molecular genetic studies in schizophrenia and bipolar affective disorder. In the present study, the -48A/G polymorphism of the DRD1 gene was estimated in patients with schizophrenia (n=407) or bipolar affective disorder (n=380), and in healthy controls (n=399). No association was found between the polymorphism studied and schizophrenia, either in the whole group of patients or in subgroups divided by gender, age at onset or predominance of positive or negative symptoms. A statistical trend was obtained for an association between this polymorphism and bipolar affective disorder (p=0.059 for genotypes, p=0.073 for alleles). The G/G genotype and G allele were significantly more frequent in patients with bipolar disorder, type II (p=0.016 for genotypes, p=0.008 for alleles), especially in the women subgroup (p=0.054 for genotypes, p=0.024 for alleles). An association between the G/G genotype and bipolar affective disorder with disease onset after 18 years of age was also found (p=0.022). These data suggest that the -48A/G polymorphism of the DRD1 gene may be involved in the etiology of bipolar disorder in a Polish population.

Pharmacogenomics: a path to predictive medicine for schizophrenia

A significant variability is observed among patients in response to antipsychotics, and is caused by a variety of factors. This review summarizes the available knowledge of associations between pharmacogenetics and drug response in schizophrenia. The multifactorial etiology of schizophrenia makes it a complex interaction of symptoms. Adopting a pharmacogenomics approach represents a unique opportunity for the prediction of response to antipsychotic drugs by investigating genes implicated with specific symptoms and side effects. A network model of the interaction/crosstalk between the neurotransmitter signaling systems is presented to emphasize the importance of the genes associated with the molecular mechanisms of the disease and drug response. These genes may serve as potential susceptibility genes and drug targets for schizophrenia. The crucial point for the identification of a significant biologic marker(s) will include not only the experimental validation of the genes involved in the neurotransmitter signaling systems, but also the availability of large exactly comparable phenotyped patients samples. Coupling our knowledge of genetic polymorphisms with clinical response data promises a bright future for rapid advances in personalized medicine.