Association between the BDNF gene and schizophrenia

Endocytosis is required for consolidation of pattern-separated memories in the perirhinal cortex

Introduction

The ability to separate similar experiences into differentiated representations is proposed to be based on a computational process called pattern separation, and it is one of the key characteristics of episodic memory. Although pattern separation has been mainly studied in the dentate gyrus of the hippocampus, this cognitive function if thought to take place also in other regions of the brain. The perirhinal cortex is important for the acquisition and storage of object memories, and in particular for object memory differentiation. The present study was devoted to investigating the importance of the cellular mechanism of endocytosis for object memory differentiation in the perirhinal cortex and its association with brain-derived neurotrophic factor, which was previously shown to be critical for the pattern separation mechanism in this structure.

Methods

We used a modified version of the object recognition memory task and intracerebral delivery of a peptide (Tat-P4) into the perirhinal cortex to block endocytosis.

Results

We found that endocytosis is necessary for pattern separation in the perirhinal cortex. We also provide evidence from a molecular disconnection experiment that BDNF and endocytosis-related mechanisms interact for memory discrimination in both male and female rats.

Discussion

Our experiments suggest that BDNF and endocytosis are essential for consolidation of separate object memories and a part of a time-restricted, protein synthesis-dependent mechanism of memory stabilization in Prh during storage of object representations.

Electroconvulsive therapy for treatment-resistant schizophrenia

BACKGROUND

Electroconvulsive therapy (ECT) involves the induction of a seizure by the administration of an electrical stimulus via electrodes usually placed bilaterally on the scalp and was introduced as a treatment for schizophrenia in 1938. However, ECT is a controversial treatment with concerns about long-term side effects such a memory loss. Therefore, it is important to determine its clinical efficacy and safety for people with schizophrenia who are not responding to their treatment.

OBJECTIVES

Our primary objective was to assess the effects (benefits and harms) of ECT for people with treatment-resistant schizophrenia.Our secondary objectives were to determine whether ECT produces a differential response in people: who are treated with unilateral compared to bilateral ECT; who have had a long (more than 12 sessions) or a short course of ECT; who are given continuation or maintenance ECT; who are diagnosed with well-defined treatment-resistant schizophrenia as opposed to less rigorously defined treatment-resistant schizophrenia (who would be expected to have a greater affective component to their illness).

SEARCH METHODS

We searched the Cochrane Schizophrenia Group's Study-Based Register of Trials including clinical trial registries on 9 September 2015 and 4 August 2017. There were no limitations on language, date, document type, or publication status for the inclusion of records in the register. We also inspected references of all the included records to identify further relevant studies.

SELECTION CRITERIA

Randomised controlled trials investigating the effects of ECT in people with treatment-resistant schizophrenia.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data. For binary outcomes, we calculated the risk ratio (RR) and its 95% confidence intervals (CIs), on an intention-to-treat basis. For continuous data, we estimated the mean difference (MD) between the groups and its 95% CIs. We employed the fixed-effect model for all analyses. We assessed risk of bias for the included studies and created 'Summary of findings' tables using the GRADE framework.

MAIN RESULTS

We included 15 studies involving 1285 participants (1264 completers with an average age of 18 to 46 years) with treatment-resistant schizophrenia. We rated most studies (14/15, 93.3%) as at high risk of bias due to issues related to the blinding of participants and personnel. Our main outcomes of interest were: (i) clinically important response to treatment; (ii) clinically important change in cognitive functioning; (iii) leaving the study early; (iv) clinically important change in general mental state; (v) clinically important change in general functioning; (vi) number hospitalised; and (vii) death. No trial reported data on death.The included trials reported useable data for four comparisons: ECT plus standard care compared with sham-ECT added to standard care; ECT plus standard care compared with antipsychotic added to standard care; ECT plus standard care compared with standard care; and ECT alone compared with antipsychotic alone.For the comparison ECT plus standard care versus sham-ECT plus standard care, only average endpoint BPRS (Brief Psychiatric Rating Scale) scores from one study were available for mental state; no clear difference between groups was observed (short term; MD 3.60, 95% CI -3.69 to 10.89; participants = 25; studies = 1; very low-quality evidence). One study reported data for service use, measured as number readmitted; there was a clear difference favouring the ECT group (short term; RR 0.29, 95% CI 0.10 to 0.85; participants = 25; studies = 1; low-quality evidence).When ECT plus standard care was compared with antipsychotics (clozapine) plus standard care, data from one study showed no clear difference for clinically important response to treatment (medium term; RR 1.23, 95% CI 0.95 to 1.58; participants = 162; studies = 1; low-quality evidence). Clinically important change in mental state data were not available, but average endpoint BPRS scores were reported. A positive effect for the ECT group was found (short-term BPRS; MD -5.20, 95% CI -7.93 to -2.47; participants = 162; studies = 1; very low-quality evidence).When ECT plus standard care was compared with standard care, more participants in the ECT group had a clinically important response (medium term; RR 2.06, 95% CI 1.75 to 2.42; participants = 819; studies = 9; moderate-quality evidence). Data on clinically important change in cognitive functioning were not available, but data for memory deterioration were reported. Results showed that adding ECT to standard care may increase the risk of memory deterioration (short term; RR 27.00, 95% CI 1.67 to 437.68; participants = 72; studies = 1; very low-quality evidence). There were no clear differences between groups in satisfaction and acceptability of treatment, measured as leaving the study early (medium term; RR 1.18, 95% CI 0.38 to 3.63; participants = 354; studies = 3; very low-quality evidence). Only average endpoint scale scores were available for mental state (BPRS) and general functioning (Global Assessment of Functioning). There were clear differences in scores, favouring ECT group for mental state (medium term; MD -11.18, 95% CI -12.61 to -9.76; participants = 345; studies = 2; low-quality evidence) and general functioning (medium term; MD 10.66, 95% CI 6.98 to 14.34; participants = 97; studies = 2; very low-quality evidence).For the comparison ECT alone versus antipsychotics (flupenthixol) alone, only average endpoint scale scores were available for mental state and general functioning. Mental state scores were similar between groups (medium-term BPRS; MD -0.93, 95% CI -6.95 to 5.09; participants = 30; studies = 1; very low-quality evidence); general functioning scores were also similar between groups (medium-term Global Assessment of Functioning; MD -0.66, 95% CI -3.60 to 2.28; participants = 30; studies = 1; very low-quality evidence).

AUTHORS' CONCLUSIONS

Moderate-quality evidence indicates that relative to standard care, ECT has a positive effect on medium-term clinical response for people with treatment-resistant schizophrenia. However, there is no clear and convincing advantage or disadvantage for adding ECT to standard care for other outcomes. The available evidence was also too weak to indicate whether adding ECT to standard care is superior or inferior to adding sham-ECT or other antipsychotics to standard care, and there was insufficient evidence to support or refute the use of ECT alone. More good-quality evidence is needed before firm conclusions can be made.

The involvement of DARPP-32 in the pathophysiology of schizophrenia

Schizophrenia is one of the most devastating heterogeneous psychiatric disorders. The dopamine hypothesis is the longest standing pathoetiologic theory of schizophrenia based on neurochemical evidences of elevated brain striatal dopamine synthesis capacity and increased dopamine release in response to stress. Dopamine and cyclic AMP-regulated phosphoprotein of relative molecular mass 32,000 (DARPP-32) is a cytosolic protein highly enriched in the medium spiny neurons of the neostriatum, considered as the most important integrator between the cortical input and the basal ganglia, and associated with motor control. Accumulating evidences has indicated the involvement of DARPP-32 in the development of schizophrenia; i. DARPP-32 phosphorylation is regulated by several neurotransmitters, including dopamine and glutamate, neurotransmitters implicated in schizophrenia pathogenesis; ii. decrease of both total and phosphorylated DARPP-32 in the prefrontal cortex are observed in schizophrenic animal models; iii. postmortem brain studies indicated decreased expression of DARPP-32 protein in the superior temporal gyrus and dorsolateral prefrontal cortex in patients with schizophrenia; iv. DARPP-32 phosphorylation is increased upon therapy with antipsychotic drugs, such as haloperidol and risperidone which improve behavioral performance in experimental animal models and patients; v. Genetic analysis of the gene coding for DARPP-32 propose an association with schizophrenia. Cumulatively, these findings implicate DARPP-32 protein in schizophrenia and propose it as a potential therapeutic target. Here, we summarize the possible roles of DARPP-32 during the development of schizophrenia and make some recommendations for future research. We propose that DARPP-32 and its interacting proteins may serve as potential therapeutic targets in the treatment of schizophrenia.

Serum brain-derived neurotrophic factor and cortical thickness are differently related in patients with schizophrenia and controls

Brain-derived neurotrophic factor (BDNF) has been implicated in neuronal plasticity, a key process related to the pathophysiology of schizophrenia. However, the relationship of peripheral levels of BDNF to cortical thickness and subcortical structures has not been extensively investigated. This study aims to investigate the relationship of peripheral serum BDNF levels to cortical thickness and volumes of the hippocampus and amygdala. Twenty-nine patients with schizophrenia and 32 healthy controls were included in this study. Structural magnetic resonance imaging (MRI) scans obtained in a 1.5 T scanner were performed in all subjects. Images were processed using Freesurfer software. Blood samples were collected on the same day of the MRI scan for BDNF peripheral levels. Vertex-wise analysis revealed significantly thinner cortex in patients compared with controls. BDNF levels and cortical thickness showed different patterns of correlation for patients and healthy controls in one cluster in the right hemisphere distributed across the supramarginal, postcentral, and inferior frontal cortices.

Biomarkers of postoperative delirium and cognitive dysfunction

Elderly surgical patients frequently experience postoperative delirium (POD) and the subsequent development of postoperative cognitive dysfunction (POCD). Clinical features include deterioration in cognition, disturbance in attention and reduced awareness of the environment and result in higher morbidity, mortality and greater utilization of social financial assistance. The aging Western societies can expect an increase in the incidence of POD and POCD. The underlying pathophysiological mechanisms have been studied on the molecular level albeit with unsatisfying small research efforts given their societal burden. Here, we review the known physiological and immunological changes and genetic risk factors, identify candidates for further studies and integrate the information into a draft network for exploration on a systems level. The pathogenesis of these postoperative cognitive impairments is multifactorial; application of integrated systems biology has the potential to reconstruct the underlying network of molecular mechanisms and help in the identification of prognostic and diagnostic biomarkers.

Common variants in the MKL1 gene confer risk of schizophrenia

Genome-wide association studies (GWAS) of schizophrenia have identified multiple risk variants with robust association signals for schizophrenia. However, these variants could explain only a small proportion of schizophrenia heritability. Furthermore, the effect size of these risk variants is relatively small (eg, most of them had an OR less than 1.2), suggesting that additional risk variants may be detected when increasing sample size in analysis. Here, we report the identification of a genome-wide significant schizophrenia risk locus at 22q13.1 by combining 2 large-scale schizophrenia cohort studies. Our meta-analysis revealed that 7 single nucleotide polymorphism (SNPs) on chromosome 22q13.1 reached the genome-wide significance level (P < 5.0×10(-8)) in the combined samples (a total of 38441 individuals). Among them, SNP rs6001946 had the most significant association with schizophrenia (P = 2.04×10(-8)). Interestingly, all 7 SNPs are in high linkage disequilibrium and located in the MKL1 gene. Expression analysis showed that MKL1 is highly expressed in human and mouse brains. We further investigated functional links between MKL1 and proteins encoded by other schizophrenia susceptibility genes in the whole human protein interaction network. We found that MKL1 physically interacts with GSK3B, a protein encoded by a well-characterized schizophrenia susceptibility gene. Collectively, our results revealed that genetic variants in MKL1 might confer risk to schizophrenia. Further investigation of the roles of MKL1 in the pathogenesis of schizophrenia is warranted.

Serum brain-derived neurotrophic factor (BDNF) and its association with remission status in Chinese patients with schizophrenia

The neurotrophin, brain-derived neurotrophic factor (BDNF), characterises a probable neurobiochemical explanation of maldevelopments in schizophrenia and is a candidate biomarker of the illness. A paucity of studies examining neurobiochemical predictors of remission in schizophrenia exists. In this study, we seek to examine if serum BDNF level is associated with remission status in a sample of Chinese patients with schizophrenia. This study did not find a significant relationship between serum BDNF and remission in patients with schizophrenia. Identification of a suitable biomarker for diagnosis, management, and prognostic outcome is crucial and warrants further study.

The neurobiological bases of memory formation: from physiological conditions to psychopathology

The formation of long-term memories is a function necessary for an adaptive survival. In the last two decades, great progress has been made in the understanding of the biological bases of memory formation. The identification of mechanisms necessary for memory consolidation and reconsolidation, the processes by which the posttraining and postretrieval fragile memory traces become stronger and insensitive to disruption, has indicated new approaches for investigating and treating psychopathologies. In this review, we will discuss some key biological mechanisms found to be critical for memory consolidation and strengthening, the role/s and mechanisms of memory reconsolidation, and how the interference with consolidation and/or reconsolidation can modulate the retention and/or storage of memories that are linked to psychopathologies.

Analysis of schizophrenia and hepatocellular carcinoma genetic network with corresponding modularity and pathways: novel insights to the immune system

Background

Schizophrenic patients show lower incidences of cancer, implicating schizophrenia may be a protective factor against cancer. To study the genetic correlation between the two diseases, a specific PPI network was constructed with candidate genes of both schizophrenia and hepatocellular carcinoma. The network, designated schizophrenia-hepatocellular carcinoma network (SHCN), was analysed and cliques were identified as potential functional modules or complexes. The findings were compared with information from pathway databases such as KEGG, Reactome, PID and ConsensusPathDB.

Results

The functions of mediator genes from SHCN show immune system and cell cycle regulation have important roles in the eitology mechanism of schizophrenia. For example, the over-expressing schizophrenia candidate genes, SIRPB1, SYK and LCK, are responsible for signal transduction in cytokine production; immune responses involving IL-2 and TREM-1/DAP12 pathways are relevant for the etiology mechanism of schizophrenia. Novel treatments were proposed by searching the target genes of FDA approved drugs with genes in potential protein complexes and pathways. It was found that Vitamin A, retinoid acid and a few other immune response agents modulated by RARA and LCK genes may be potential treatments for both schizophrenia and hepatocellular carcinoma.

Conclusions

This is the first study showing specific mediator genes in the SHCN which may suppress tumors. We also show that the schizophrenic protein interactions and modulation with cancer implicates the importance of immune system for etiology of schizophrenia.

The interaction of BDNF and NTRK2 gene increases the susceptibility of paranoid schizophrenia

The association between BDNF gene functional Val66Met polymorphism rs6265 and the schizophrenia is far from being consistent. In addition to the heterogeneous in schizophrenia per se leading to the inconsistent results, the interaction among multi-genes is probably playing the main role in the pathogenesis of schizophrenia, but not a single gene. Neurotrophic tyrosine kinase receptor 2 (NTRK2) is the high-affinity receptor of BDNF, and was reported to be associated with mood disorders, though no literature reported the association with schizophrenia. Thus, in the present study, total 402 patients with paranoid schizophrenia (the most common subtype of schizophrenia) and matched 406 healthy controls were recruited to investigate the role of rs6265 in BDNF, three polymorphisms in NTRK2 gene (rs1387923, rs2769605 and rs1565445) and their interaction in the susceptibility to paranoid schizophrenia in a Chinese Han population. We did not observe significant differences in allele and genotype frequencies between patients and healthy controls for all four polymorphisms separately. The haplotype analysis also showed no association between haplotype of NTRK2 genes (rs1387923, rs2769605, and rs1565445) and paranoid schizophrenia. However, we found the association between the interaction of BDNF and NTRK2 with paranoid schizophrenia by using the MDR method followed by conventional statistical analysis. The best gene-gene interaction model was a three-locus model (BDNF rs6265, NTRK2 rs1387923 and NTRK2 rs2769605), in which one low-risk and three high-risk four-locus genotype combinations were identified. Our findings implied that single polymorphism of rs6265 rs1387923, rs2769605, and rs1565445 in BDNF and NTRK2 were not associated with the development of paranoid schizophrenia in a Han population, however, the interaction of BDNF and NTRK2 genes polymorphisms (BDNF-rs6265, NTRK2-rs1387923 and NTRK2-rs2769605) may be involved in the susceptibility to paranoid schizophrenia.

Association of BDNF gene polymorphisms with schizophrenia and clinical symptoms in a Chinese population

The neurodevelopmental hypothesis is well established in schizophrenia. Accumulating evidence has shown that BDNF may be involved in the pathogenesis of schizophrenia. This study aimed to investigate the potential association of BDNF gene polymorphisms with susceptibility to schizophrenia and with the psychopathological symptoms in patients with schizophrenia in a Han Chinese population. Three polymorphisms (rs6265, rs12273539, and rs10835210) of the BDNF gene were analyzed in a case-control study of 709 Han Chinese individuals (375 patients and 334 controls). The patients' psychopathology was assessed using the positive and negative syndrome scale (PANSS). We found no significant differences in the genotype and allele distributions of all three polymorphisms between the patient and control groups; however, we found a trend toward to significant overall difference in the estimated haplotype frequencies, with more frequent haplotype ATC of rs6265-rs12273539-rs10835210 in the schizophrenic patients than in controls (P = 0.027). The quantitative trait analysis by the UNPHASED program showed significant associations between the rs6265 (A)-rs12273539 (C)-rs10835210 (A) haplotype and negative symptom scores from the PANSS (x(2)  = 5.79, P = 0.016). Our findings suggest that the BDNF gene polymorphisms may play a small effect on susceptibility to schizophrenia, but may contribute to the negative symptoms of the disease.

Brain-derived neurotrophic factor (BDNF) Val(66)Met polymorphism differentially predicts hippocampal function in medication-free patients with schizophrenia

A Val(66)Met single-nucleotide polymorphism (SNP) in the brain-derived neurotrophic factor (BDNF) gene impairs activity-dependent BDNF release in cultured hippocampal neurons and predicts impaired memory and exaggerated basal hippocampal activity in healthy humans. Several clinical genetic association studies along with multi-modal evidence for hippocampal dysfunction in schizophrenia indirectly suggest a relationship between schizophrenia and genetically determined BDNF function in the hippocampus. To directly test this hypothesized relationship, we studied 47 medication-free patients with schizophrenia or schizoaffective disorder and 74 healthy comparison individuals with genotyping for the Val(66)Met SNP and [(15)O]H(2)O positron emission tomography (PET) to measure resting and working memory-related hippocampal regional cerebral blood flow (rCBF). In patients, harboring a Met allele was associated with significantly less hippocampal rCBF. This finding was opposite to the genotype effect seen in healthy participants, resulting in a significant diagnosis-by-genotype interaction. Exploratory analyses of interregional resting rCBF covariation revealed a specific and significant diagnosis-by-genotype interaction effect on hippocampal-prefrontal coupling. A diagnosis-by-genotype interaction was also found for working memory-related hippocampal rCBF change, which was uniquely attenuated in Met allele-carrying patients. Thus, both task-independent and task-dependent hippocampal neurophysiology accommodates a Met allelic background differently in patients with schizophrenia than in control subjects. Potentially consistent with the hypothesis that cellular sequelae of the BDNF Val(66)Met SNP interface with aspects of schizophrenic hippocampal and frontotemporal dysfunction, these results warrant future investigation to understand the contributions of unique patient trait or state variables to these robust interactions.

BDNF serum concentrations in first psychotic episode drug-naïve schizophrenic patients: associations with personality and BDNF Val66Met polymorphism

AIMS

To investigate the relationship among brain derived neurotrophic factor (BDNF) serum concentrations, BDNF Val66Met polymorphism and personality profile in drug-naïve schizophrenic patients with first-episode psychosis (FEP) and healthy participants.

MAIN METHODS

This cross-sectional study included fifty FEP patients and fifty healthy participants who served as controls. To study their personality profile the standardized Greek version of the Alternative Five-Factor Zuckerman-Kuhlman Personality Questionnaire (ZKPQ) was administered. Serum BDNF levels were measured and genotyping of BDNF Val66Met polymorphism was performed in patients and healthy subjects.

KEY FINDINGS

FEP patients presented lower BDNF serum concentrations (P=0.002) and higher scores in ZKPQ Neuroticism (P=0.001) and Aggression-Hostility (P=0.002) scales while lower scores in the ZKPQ Sociability scale (P<0.001) than healthy participants. Multivariate analysis revealed that the odds of being assessed with FEP were 0.4 times lower in those with higher BDNF values (P<0.001) and 1.8 times greater in those with higher Neuroticism scores (P<0.001). There were no significant differences with respect to the Val66Met polymorphism between patients and healthy participants.

SIGNIFICANCE

Reduced BDNF serum concentrations along with higher Neuroticism scores might be associated with FEP. A complex interplay between BDNF serum concentrations, personality traits, BDNF Val66Met polymorphism, and psychotic symptomatology has been arisen but further investigation is needed to better clarify the observed associations.

A gene expression and systems pathway analysis of the effects of clozapine compared to haloperidol in the mouse brain implicates susceptibility genes for schizophrenia

Clozapine has markedly superior clinical properties compared to other antipsychotic drugs but the side effects of agranulocytosis, weight gain and diabetes limit its use. The reason why clozapine is more effective is not well understood. We studied messenger RNA (mRNA) gene expression in the mouse brain to identify pathways changed by clozapine compared to those changed by haloperidol so that we could identify which changes were specific to clozapine. Data interpretation was performed using an over-representation analysis (ORA) of gene ontology (GO), pathways and gene-by-gene differences. Clozapine significantly changed gene expression in pathways related to neuronal growth and differentiation to a greater extent than haloperidol; including the microtubule-associated protein kinase (MAPK) signalling and GO terms related to axonogenesis and neuroblast proliferation. Several genes implicated genetically or functionally in schizophrenia such as frizzled homolog 3 (FZD3), U2AF homology motif kinase 1 (UHMK1), pericentriolar material 1 (PCM1) and brain-derived neurotrophic factor (BDNF) were changed by clozapine but not by haloperidol. Furthermore, when compared to untreated controls clozapine specifically regulated transcripts related to the glutamate system, microtubule function, presynaptic proteins and pathways associated with synaptic transmission such as clathrin cage assembly. Compared to untreated controls haloperidol modulated expression of neurotoxic and apoptotic responses such as NF-kappa B and caspase pathways, whilst clozapine did not. Pathways involving lipid and carbohydrate metabolism and appetite regulation were also more affected by clozapine than by haloperidol.

Reprint of: Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.

Lack of Association between Brain-Derived Neurotrophic Factor Gene Val66Met Polymorphisms and Generalized Social Anxiety Disorder in Korean Population

OBJECTIVE

Several lines of evidence suggest that brain-derived neurotrophic factor (BDNF) plays a role in the pathophysiology of anxiety. We analyzed the association of the BDNF gene polymorphism, G196A (val66met), in the coding region of exon XIIIA in chromosome 11p13, and generalized social anxiety disorder (GSAD).

METHODS

Patients with GSAD (n=73) and age-matched control subjects (n=152) were tested for the BDNF (val66met) polymorphism. A clinical interview and a Mini-International Neuropsychiatric Interview were conducted by trained psychiatrists in order to diagnose GSAD. The symptomatic characteristics of the GSAD patients were assessed with the Hamilton Anxiety Rating Scale, the Beck Anxiety Inventory, the Retrospective Self Report of Inhibition, the Spielberger State-Trait Anxiety Inventory, and the Liebowitz Social Anxiety Scale.

RESULTS

There were no significant differences in the frequencies of the genotypes (χ(2)=0.961, degree of freedom [df]=2, p=0.619), alleles (χ(2)=0.415, df=1, p=0.519), or allele (methionine) carriers (χ(2)=0.019, df=1, p=0.889) between the patients and controls. In addition, when we compared the severity of social anxiety symptom as determined by the clinical scales with the genotypes of the BDNF gene, we could not find any significant differences between the genotypes or allele carriers.

CONCLUSION

These results do not support the hypothesis that the BDNF gene might be a candidate gene for susceptibility or severity of GSAD in the Korean population in this study.

Effects of BDNF polymorphisms on brain function and behavior in health and disease

Brain-derived neurotrophic factor (BDNF), the most abundant neurotrophin in the brain, serves an important role during brain development and in synaptic plasticity. Given its pleiotropic effects in the central nervous system, BDNF has been implicated in cognitive function and personality development as well as the pathogenesis of various psychiatric disorders. Thus, BDNF is considered an attractive candidate gene for the study of healthy and diseased brain function and behaviors. Over the past decade, many studies have tested BDNF genetic association, particularly its functional Val66Met polymorphism, with psychiatric diseases, personality disorders, and cognitive function. Although many reports indicated a possible role for BDNF genetic effects in mental problems or brain function, other reports were unable to replicate the findings. The conflicting results in BDNF genetic studies may result from confounding factors such as age, gender, other environmental factors, sample size, ethnicity and phenotype assessment. Future studies with more homogenous populations, well-controlled confounding factors, and well-defined phenotypes are needed to clarify the BDNF genetic effects on mental diseases and human behaviors.

The role of dopaminergic signalling during larval zebrafish brain development: a tool for investigating the developmental basis of neuropsychiatric disorders

Neurodevelopment depends on intrinsic and extrinsic factors that influence the overall pattern of neurogenesis and neural circuit formation, which has a direct impact on behaviour. Defects in dopamine signalling and brain morphology at a relatively early age, and mutations in neurodevelopmental genes are strongly correlated with several neuropsychiatric disorders. This evidence supports the hypothesis of a neurodevelopmental origin of at least some forms of mental illness. Zebrafish (Danio rerio) has emerged as an important vertebrate model system in biomedical research. The ease with which intrinsic and extrinsic factors can be altered during early development, the relatively conserved dopaminergic circuit organisation in the larval brain, and the emergence of simple sensorimotor behaviours very early in development are some of the appealing features that make this organism advantageous for developmental brain and behaviour research. Thus, examining the impact of altered dopamine signalling and disease related genetic aberrations during zebrafish development presents a unique opportunity to holistically analyse the in vivo biochemical, morphological and behavioural significance of altered dopamine signalling during a crucial period of development using a highly tractable vertebrate model organism. Ultimately, this information will shed new light on potential therapeutic targets for the treatment of schizophrenia and perhaps serve as a paradigm for investigating the neurodevelopmental origin of other psychiatric disorders.

Neuroplasticity signaling pathways linked to the pathophysiology of schizophrenia

Schizophrenia is a severe mental illness that afflicts nearly 1% of the world's population. One of the cardinal pathological features of schizophrenia is perturbation in synaptic connectivity. Although the etiology of schizophrenia is unknown, it appears to be a developmental disorder involving the interaction of a potentially large number of risk genes, with no one gene producing a strong effect except rare, highly penetrant copy number variants. The purpose of this review is to detail how putative schizophrenia risk genes (DISC-1, neuregulin/ErbB4, dysbindin, Akt1, BDNF, and the NMDA receptor) are involved in regulating neuroplasticity and how alterations in their expression may contribute to the disconnectivity observed in schizophrenia. Moreover, this review highlights how many of these risk genes converge to regulate common neurotransmitter systems and signaling pathways. Future studies aimed at elucidating the functions of these risk genes will provide new insights into the pathophysiology of schizophrenia and will likely lead to the nomination of novel therapeutic targets for restoring proper synaptic connectivity in the brain in schizophrenia and related disorders.

Association study of BDNF and DRD3 genes in schizophrenia diagnosis using matched case-control and family based study designs

Schizophrenia (SCZ) is a severe neuropsychiatric disorder with prominent genetic etiologic factors. The dopamine receptor DRD3 gene is a strong candidate in genetic studies of SCZ because of the dopamine hypothesis of SCZ and the selective expression of D(3) in areas of the limbic system implicated in the disease. We examined 15 single-nucleotide polymorphisms (SNPs) in DRD3 in our sample of European origin consisting of 95 small nuclear SCZ families and 167 case-control pairs. We also examined four BDNF SNPs in our samples because of evidence for BDNF regulation of DRD3 expression (Guillin et al., 2001). We found a nominally significant genotypic association with rs7633291 and allelic association with rs1025398 alleles. However, these observations did not survive correction for multiple testing. We did not find a statistically significant association with the other DRD3 and BDNF polymorphisms. Taken together, the results from the present study suggest that BDNF and DRD3 may not be involved in SCZ susceptibility.

Population genetic study of the brain-derived neurotrophic factor (BDNF) gene

Genetic variants in the brain-derived neurotrophic factor (BDNF) gene, predominantly the functional Val66Met polymorphism, have been associated with risk of bipolar disorder and other psychiatric disorders. However, not all studies support these findings, and overall the evidence for the association of BDNF with disease risk is weak. As differences in population genetic structure between patient samples could cause discrepant or spurious association results, we investigated this possibility by carrying out population genetic analyses of the BDNF genomic region. Substantial variation was detected in BDNF coding region single-nucleotide polymorphism (SNP) allele and haplotype frequencies between 58 global populations, with the derived Met allele of Val66Met ranging in frequency from 0 to 72% across populations. F(ST) analyses to assess diversity in the HapMap populations determined that the Val66Met F(ST) value was at the 99.8th percentile among all SNPs in the genome. As the BDNF population genetic differences may be due to local selection, we performed the long-range haplotype test for selection using 68 SNPs spanning the BDNF genomic region in 12 European-derived pedigrees. Evidence for positive selection was found for a high-frequency Val-carrying haplotype, with a relative extended haplotype homozygosity value above the 99 th percentile compared with HapMap data (P=4.6 x 10(-4)). In conclusion, we observed considerable BDNF allele and haplotype diversity among global populations and evidence for positive selection at the BDNF locus. These phenomena can have a profound impact on the detection of disease susceptibility genes and must be considered in gene association studies of BDNF.

Fine mapping of AHI1 as a schizophrenia susceptibility gene: from association to evolutionary evidence

In previous studies, we identified a locus for schizophrenia on 6q23.3 and proposed the Abelson helper integration site 1 (AHI1) as the candidate gene. AHI1 is expressed in the brain and plays a key role in neurodevelopment, is involved in Joubert syndrome, and has been recently associated with autism. The neurodevelopmental role of AHI1 fits with etiological hypotheses of schizophrenia. To definitively confirm our hypothesis, we searched for associations using a dense map of the region. Our strongest findings lay within the AHI1 gene: single-nucleotide polymorphisms rs11154801 and rs7759971 showed significant associations (P=6.23E-06; P=0.84E-06) and haplotypes gave P values in the 10E-8 to 10E-10 range. The second highest significant region maps close to AHI1 and includes the intergenic region between BC040979 and PDE7B (rs2038549 at P=9.70E-06 and rs1475069 at P=6.97E-06), and PDE7B and MAP7. Using a sample of Palestinian Arab families to confirm these findings, we found isolated signals. While these results did not retain their significance after correction for multiple testing, the joint analysis across the 2 samples supports the role of AHI1, despite the presence of heterogeneity. Given the hypothesis of positive selection of schizophrenia genes, we resequenced a 11 kb region within AHI1 in ethnically defined populations and found evidence for a selective sweep. Network analysis indicates 2 haplotype clades, with schizophrenia-susceptibility haplotypes clustering within the major clade. In conclusion, our data support the role of AHI1 as a susceptibility gene for schizophrenia and confirm it has been subjected to positive selection, also shedding light on new possible candidate genes, MAP7 and PDE7B.

Genetic study of BDNF, DRD3, and their interaction in tardive dyskinesia

Tardive dyskinesia (TD) is a neuroleptic-induced movement disorder. Its pathophysiology is unclear. The most consistent genetic findings have shown an association with the Ser9Gly polymorphism of the DRD3 gene. However, only few polymorphisms within DRD3 has been tested, and a comprehensive examination of DRD3 in TD is still lacking. Further, brain-derived neurotrophic factor (BDNF), a neuronal growth and survival peptide, regulates DRD3 expression and may be involved in the neuronal degeneration observed in TD. In the present study, we investigated 15 tag DRD3 polymorphisms and four tag BDNF polymorphisms for association with TD in our sample of Caucasian schizophrenia patients (N=171). While BDNF markers showed no association, a haplotype containing rs3732782, rs905568, and rs7620754 in the 5' region of DRD3 was associated with TD diagnosis (p[10,000 permutations]=0.007). We also found evidence of interaction between BDNF and DRD3 polymorphisms. Further studies are needed to confirm these findings.

Interspecies comparisons of functional genetic variations and their implications in neuropsychiatry

Animal studies are important for the identification and functional characterization of the biological substrates underlying complex psychiatric disorders. However, novel insights into the relationship between the genome and behavior are needed for the development of fully valid translational models. Based on the notion that in different species, the same genes may independently give rise to alleles with similar functional and phenotypic effects, either under similar selection or through similar genomic mechanisms, we propose the use of genetic validity as a tool for identifying analogous pathology between animals and human neuropsychiatric disorders. Furthermore, the identification of copy number variants which disrupt entire genes, reinforces the notion that transgenic animals, such as knockouts or knock-ins, may provide unexpectedly valid disease models for psychiatric traits. To illustrate interspecies comparison of genetic variations in relation to neurobehavioral traits, examples are provided for the BDNF, COMT, and DISC1 genes in mouse and man. We propose that alignment of individual genetic variations with endophenotypes obtained from mice and across categories of neuropsychiatric disorders will provide an important step in translational research.

Genomic imprinting in the development and evolution of psychotic spectrum conditions

I review and evaluate genetic and genomic evidence salient to the hypothesis that the development and evolution of psychotic spectrum conditions have been mediated in part by alterations of imprinted genes expressed in the brain. Evidence from the genetics and genomics of schizophrenia, bipolar disorder, major depression, Prader-Willi syndrome, Klinefelter syndrome, and other neurogenetic conditions support the hypothesis that the etiologies of psychotic spectrum conditions commonly involve genetic and epigenetic imbalances in the effects of imprinted genes, with a bias towards increased relative effects from imprinted genes with maternal expression or other genes favouring maternal interests. By contrast, autistic spectrum conditions, including Kanner autism, Asperger syndrome, Rett syndrome, Turner syndrome, Angelman syndrome, and Beckwith-Wiedemann syndrome, commonly engender increased relative effects from paternally expressed imprinted genes, or reduced effects from genes favouring maternal interests. Imprinted-gene effects on the etiologies of autistic and psychotic spectrum conditions parallel the diametric effects of imprinted genes in placental and foetal development, in that psychotic spectrum conditions tend to be associated with undergrowth and relatively-slow brain development, whereas some autistic spectrum conditions involve brain and body overgrowth, especially in foetal development and early childhood. An important role for imprinted genes in the etiologies of psychotic and autistic spectrum conditions is consistent with neurodevelopmental models of these disorders, and with predictions from the conflict theory of genomic imprinting.

Association study of brain-derived neurotrophic factor (BDNF) and LIN-7 homolog (LIN-7) genes with adult attention-deficit/hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a common psychiatric disorder with a large genetic component that has been shown to persist into adulthood in 30-60% of childhood ADHD cases. Adult ADHD confers an increased risk of ADHD in relatives when compared to childhood ADHD, possibly due to a greater genetic liability than the childhood form. Brain-derived neurotrophic factor (BDNF) is a neurotrophin expressed in the brain throughout life and is involved in survival, differentiation, and synaptic plasticity of several neuronal systems including dopaminergic pathways. Mammalian LIN-7 homolog is selectively expressed in specific neuronal populations and is involved in the postsynaptic density of neuronal synapses. LIN-7 is also a positional candidate, as it lies immediately downstream of BDNF. We tested for association between five BDNF polymorphisms, two LIN-7 polymorphisms and adult ADHD. The sample consisted of 80 trios comprised of an adult ADHD proband and their biological parents and an independent sample of 121 adult ADHD cases and a corresponding number of sex, age, and ethnically matched controls (total 201 probands). Allelic and haplotype association was found between both BDNF and adult ADHD, and LIN-7 and adult ADHD. HapMap indicates BDNF and LIN-7 occur in different haplotype blocks, though some linkage disequilibrium exists between the SNPs in these adjacent genes. Further investigations into the pathologic mechanisms of BDNF and LIN-7 in adult ADHD are required.

Increased alpha-defensins as a blood marker for schizophrenia susceptibility

Schizophrenia is a severe psychotic illness affecting 1% of the general population. There are no consistent pathological features, and the disorder is defined by a complex symptomatology, which overlaps with other psychiatric illnesses. Diagnosis is based on a clinical interview, relying on the patient meeting criteria according to diagnosis manuals, including Diagnostic and Statistical Manual of Mental Disorders, 4th Ed. and International Statistical Classification of Diseases, 10th Revision. Because of the ambiguous symptoms, the diagnostic process can take many months and often years. Rapid and effective treatment has been shown to impact positively on disease progression and outcome, and it is therefore important to identify disease-associated biomarkers allowing early diagnosis. Reliable biomarkers can be used for the development of diagnostic tests and may also help us understand the underlying pathology of this disorder. In the present study, proteins from anti-CD3 stimulated and unstimulated peripheral blood T cell lysates from 15 minimally medicated and unmedicated patients and 15 age-, sex-, race-, and smoking-matched controls were profiled on cation exchange (CM10) chips using SELDI-TOF. Partial least squares discriminate analysis was used to separate patient and control groups according to the expression of 108 detected peaks, and two peaks of 3,374 and 3,450 Da, corresponding to alpha-defensins based on masses and cationic properties, were found to contribute significantly to the separation of patient and control groups. Reduction of T cell lysates with DTT resulted in a 6-Da shift in the mass of these peaks consistent with the presence of three cysteine bonds in the structure, confirming them as alpha-defensins. Quantification of alpha-defensins in T cell lysates from six patients and 18 healthy controls was carried out by ELISA, which also showed that alpha-defensin levels were significantly increased in patient lysates when compared with matched controls (p = 0.0197). Plasma from 21 monozygotic twins discordant for schizophrenia and eight healthy unaffected twin pairs was also analyzed for the expression of alpha-defensins by ELISA. Notably both affected and unaffected twins were found to have significantly elevated alpha-defensin levels compared with healthy control twin pairs (p = 0.0014 and p = 0.0115, respectively). Increased expression of alpha-defensins in unaffected as well as affected discordant monozygotic twins is of particular interest as monozygotic twins share genes and usually environmental upbringing. The unaffected twin therefore represents the biological and environmental risk of developing schizophrenia in the absence of overt symptomatology and therapeutic medication. These findings suggest that alpha-defensins could be an important early indicator of the risk of schizophrenia.

A quantitative association study between schizotypal traits and COMT, PRODH and BDNF genes in a healthy Chinese population

Previous studies have suggested that catechol-O-methyltransferase (COMT), proline dehydrogenase (PRODH), and brain-derived neurotrophic factor (BDNF) genes are possible susceptibility genes for schizophrenia. We hypothesized that these genes are also associated with schizotypal traits, which are heritable and related to schizophrenia. We genotyped five single nucleotide polymorphism (SNPs) from the COMT, PRODH and BDNF genes, and performed a series of association analyses between alleles, genotypes or haplotypes, and quantitative schizotypal trait scores derived from the Schizotypal Personality Questionnaire (SPQ), in 465 Chinese healthy subjects. We found that 'years of education' was a major influence on seven out of nine schizotypal components, three schizotypal factors and the total SPQ scores. Molecular genetic analysis of COMT, PRODH and BDNF genes showed no significant effects of any variants on schizotypal components or factors of SPQ after correction for multiple testing, although there were weak association between COMT Val158Met (rs4680G/A) and the odd speech subscale (allele-wise, P=0.04; genotype-wise, P=0.049), between COMT Val158Met (rs4680G/A) and the suspiciousness subscale (genotype-wise, P=0.024), and between BDNF Val66Met and the Factor 2 interpersonal measure (genotype-wise, P=0.027) before correction. Furthermore, we found SNP Val158Met (rs4680) of the COMT gene significantly influenced the scores of some of schizotypal traits including total SPQ score, the disorganization factor and the constricted affect subscale in male subjects only. However, the effect was in the opposite direction of an earlier association with the SPQ reported by Avramopoulos et al. [Avramopoulos, D., Stefanis, N.C., Hantoumi, I., Smyrnis, N., Evdokimidis, I., Stefanis, C.N., 2002. Higher scores of self reported schizotypy in healthy young males carrying the COMT high activity allele. Molecular Psychiatry 7, 706-711]. We conclude that SNP Val158Met (rs4680) in the COMT gene may be associated with some schizotypal traits in male subjects, but our results are not conclusive.

Brain-derived neurotrophic factor and its receptor tropomyosin-related kinase B in the mechanism of action of antidepressant therapies

The focus of this review is to critically examine and review the literature on the role of brain-derived neurotrophic factor (BDNF) and its primary receptor, tropomyosin-related kinase B (TrkB), in the actions of pharmacologically diverse antidepressant treatments for depression. This will include a review of the studies on the regulation of BDNF and TrkB by different types of antidepressant drug treatments and animal in models of depression, as well as altered levels of BDNF and TrkB in the blood and postmortem brain of patients with depression. Results from clinical and basic studies have demonstrated that stress and depression decrease BDNF expression and neurogenesis and antidepressant treatment reverses or blocks these effects, leading to the neurotrophic hypothesis of depression. Clinical studies demonstrate an association between BDNF levels and several disorders, including depression, epilepsy, bipolar disorder, Parkinson's and Alzheimer's diseases. Physical activity and diet exert neurotrophic effects and positively modulate BDNF levels. A common single nucleotide polymorphism (SNP) in the BDNF gene, a methionine substitution for valine, is associated with alterations in brain anatomy and memory, but what role it has in clinical disorders is unclear. Findings suggest that early childhood events and adult stress produce neurodegenerative alterations in the brain that can eventually cause breakdown of information processing in the neuronal networks regulating mood. Antidepressant treatments elevate activity-dependent neuronal plasticity by activating BDNF, thereby gradually restoring network function and ultimately mood.

Brain-derived neurotrophic factor Val66Met and psychiatric disorders: meta-analysis of case-control studies confirm association to substance-related disorders, eating disorders, and schizophrenia

BACKGROUND

There is an increasing recognition that the pathophysiology of mental disorders could be the result of deregulation of synaptic plasticity with alterations of neurotrophins. The valine (Val)66-to-methionine (Met) variant, located in the pro brain-derived neurotrophic factor (BDNF) sequence, has been extensively studied through linkage and association approaches in several psychiatric disorders.

METHODS

We performed a meta-analysis restricted to individual case-control studies in different categories of mental disorders and BDNF Val66Met polymorphism. We included data from 39 case-control studies encompassing psychiatric phenotypes: eating disorders, substance-related disorders, mood disorders, and schizophrenia, among others.

RESULTS

The association of Val66Met was confined to three diagnoses: substance-related disorders, eating disorders, and schizophrenia. The Val/Met and the Met/Met genotypes increase the risk for eating disorders up to 33%, while these same genotypes confer a 21% protective effect in substance-related disorders. The homozygous carriers Met/Met showed a 19% increased risk of schizophrenia with respect to the heterozygous state.

CONCLUSIONS

The study confirms the association of Val66Met to substance-related disorders, eating disorders, and schizophrenia. It remains to be determined if other variants in tight linkage disequilibrium with Val66Met could configure an extended functional haplotype that would explain observed discrepancies in risk estimations across studies.

Brain-derived neurotrophic factor gene C-270T and Val66Met functional polymorphisms and risk of schizophrenia: a moderate-scale population-based study and meta-analysis

BACKGROUND

Lines of evidence have suggested that the brain-derived neurotrophic factor (BDNF) gene may be involved in the pathogenesis of schizophrenia. Two common functional polymorphisms C-270T and Val66Met within the BDNF gene were first reported by Kunugi et al. [Kunugi, H., Nanko, S., Hirasawa, H., Kato, N., Nabika, T., Kobayashi, S., 2003. Brain-derived neurotrophic factor gene and schizophrenia: polymorphism screening and association analysis. Schizophr. Res. 62, 281-283.] and pls expand this too: Hong et al. (2003) to be significantly associated with schizophrenia. However, subsequently several studies obtained conflicting results.

METHODS

We compared the allele/genotype frequencies of the C-270T and Val66Met polymorphisms and the haplotype frequencies at the two polymorphisms in a moderate independent patient-control sample from the Han Chinese population. Two systematic meta-analyses were performed to assess the collective evidence for association across studies for each of the two polymorphisms.

RESULTS

No statistically significant differences were found in allele or genotype or haplotype frequencies between patient and normal control subjects for either of the two polymorphisms. On the other hand, the meta-analysis of all published population-based association studies showed statistically significant evidence for heterogeneity among each of the two polymorphisms. Stratification of the studies by ethnicity of the samples yielded no significant evidence for an association with the polymorphisms in the Caucasian population (for C-270T polymorphism: pooled OR(Caucasian)=0.736, 95% CI=0.476-1.139, p=0.169; for Val66Met polymorphism: pooled OR(Caucasian)=1.027, 95% CI=0.796-1.325, p=0.835), nor in the Asian population (for C-270T polymorphism: pooled OR(Asian)=0.445, 95% CI=0.144-1.373, p=0.159; for Val66Met polymorphism: pooled OR(Asian)=0.962, 95% CI=0.820-1.128, p=0.635).

CONCLUSIONS

Our population-based study and meta-analysis demonstrate that the BDNF C-270T and Val66Met polymorphisms do not play major roles in the susceptibility to schizophrenia in either Caucasian or Asian populations. But we can not rule out the possibility that other polymorphisms with the BDNF gene are involved in the pathophysiology of schizophrenia.

Brain-derived neurotrophic factor and risk of schizophrenia: An association study and meta-analysis

Brain-derived neurotrophic factor (BDNF) is the most widely distributed neurotrophin in the central nervous system (CNS), and performs many biological functions such as neural survival, differentiation, and plasticity. Previous studies have suggested that variants in the BDNF gene increase the risk of schizophrenia. In this study, we genotyped one (GT)n dinucleotide repeat and three SNPs (rs6265, rs2030324, and rs2883187) in a Chinese sample (617 cases and 672 controls). In addition, we performed an updated meta-analysis based on 16 population-based case-control studies examining association between rs6265 and schizophrenia. In single-locus analysis, no significant association was found between BDNF polymorphisms and schizophrenia in our subjects. The meta-analysis based on Asian and Caucasian subjects did not give positive result that rs6265 is associated with schizophrenia. However, haplotype analysis found a common four-locus haplotype is protective against schizophrenia (Case 3.1% vs Control 7%, p=0.0011). Our data provides evidence that BDNF is a susceptibility gene for schizophrenia in Chinese subjects.

Brain-derived neurotrophic factor in schizophrenia and its relation with dopamine

The brain-derived neurotrophic factor (BDNF) belongs to the neurotrophins family and has a role in proliferation, differentiation of neurons but also as a neurotransmitter. This neurotrophin has received much attention during the last year in regard of the pathophysiology of schizophrenia. Results of genetic studies conducted in schizophrenia support a role for BDNF in schizophrenia and in brain function associated with the disorder. The changes of BDNF observed in the brain and in the plasma of patients with schizophrenia have generated results that can be interpreted either as a hallmark of the disease or a consequence of antipsychotic drugs. Antipsychotic drugs act by blocking the dopamine transmission at the dopamine D2-like receptors. BDNF controls the expression of one of these D2-like receptors, the dopamine D3 receptor. This raises the hypothesis of a link between cortical area, via BDNF, and the dopamine neurotransmission pathway in schizophrenia and its treatment.

Candidate genes, pathways and mechanisms for alcoholism: an expanded convergent functional genomics approach

We describe a comprehensive translational approach for identifying candidate genes for alcoholism. The approach relies on the cross-matching of animal model brain gene expression data with human genetic linkage data, as well as human tissue data and biological roles data, an approach termed convergent functional genomics. An analysis of three animal model paradigms, based on inbred alcohol-preferring (iP) and alcohol-non-preferring (iNP) rats, and their response to treatments with alcohol, was used. A comprehensive analysis of microarray gene expression data from five key brain regions (frontal cortex, amygdala, caudate-putamen, nucleus accumbens and hippocampus) was carried out. The Bayesian-like integration of multiple independent lines of evidence, each by itself lacking sufficient discriminatory power, led to the identification of high probability candidate genes, pathways and mechanisms for alcoholism. These data reveal that alcohol has pleiotropic effects on multiple systems, which may explain the diverse neuropsychiatric and medical pathology in alcoholism. Some of the pathways identified suggest avenues for pharmacotherapy of alcoholism with existing agents, such as angiotensin-converting enzyme (ACE) inhibitors. Experiments we carried out in alcohol-preferring rats with an ACE inhibitor show a marked modulation of alcohol intake. Other pathways are new potential targets for drug development. The emergent overall picture is that physical and physiological robustness may permit alcohol-preferring individuals to withstand the aversive effects of alcohol. In conjunction with a higher reactivity to its rewarding effects, they may able to ingest enough of this nonspecific drug for a strong hedonic and addictive effect to occur.

Brain-derived neurotrophic factor (BDNF) gene and rapid-cycling bipolar disorder: family-based association study

BACKGROUND

We have previously reported the Val66Met and GT(n) repeat polymorphisms of the brain-derived neurotrophic factor (BDNF) gene to be associated with bipolar disorder. However, these findings have not been replicated consistently.

AIMS

To dissect the association of the BDNF gene with bipolar disorder by examining additional markers at the DNA level and by testing the illness categories of bipolar disorder I and II and rapid cycling.

METHOD

We performed a family-based association study and haplotype analyses with 312 nuclear families using four single nucleotide polymorphisms (SNPs) and the Val66Met and GT(n) repeat polymorphisms.

RESULTS

The SNPs hCV11592756 and rs2049045, the Val66Met and GT(n) were significantly associated with bipolar disorder using transmission disequilibrium analyses (P=0.02, 0.009, 0.001 and 0.008 respectively). The effect atthese markers was mainly driven by the rapid-cycling patients.

CONCLUSIONS

Within bipolar disorder, variation in the BDNF gene appears to predict risk for developing rapid cycling according to DSM-IV. Incorporating this clinical sub-phenotyping into other studies of the BDNF gene may help to resolve some of the inconsistencies reported thus far concerning BDNF and bipolar disorder.

A complex polymorphic region in the brain-derived neurotrophic factor (BDNF) gene confers susceptibility to bipolar disorder and affects transcriptional activity

Previous studies have suggested that genetic variations in the brain-derived neurotrophic factor (BDNF) gene may be associated with several neuropsychiatric diseases including bipolar disorder. The present study examined a microsatellite polymorphism located approximately 1.0 kb upstream of the translation initiation site of the BDNF gene for novel sequence variations, association with bipolar disorder, and effects on transcriptional activity. Detailed sequencing analysis revealed that this polymorphism is not a simple dinucleotide repeat, but it is highly polymorphic with a complex structure containing three types of dinucleotide repeats, insertion/deletion, and nucleotide substitutions that gives rise to a total of 23 novel allelic variants. We obtained evidence supporting the association between this polymorphic region (designated as BDNF-linked complex polymorphic region (BDNF-LCPR)) and bipolar disorder. One of the major alleles ('A1' allele) was significantly more common in patients than in controls (odds ratio 2.8, 95% confidential interval 1.5-5.3, P=0.001). Furthermore, a luciferase reporter gene assay in rat primary cultured neurons suggests that this risk allele (A1) has a lower-transcription activity, compared to the other alleles. Our results suggest that the BDNF-LCPR is a functional variation that confers susceptibility to bipolar disorder and affects transcriptional activity of the BDNF gene.

Brain-derived neurotrophic factor gene (BDNF) variants and schizophrenia: an association study

Polymorphisms in the brain-derived neurotrophic factor (BDNF) gene have been suggested to be associated with schizophrenia. In a replication attempt, Swedish patients with schizophrenia (n=187) and control subjects (n=275) were assessed for four BDNF gene polymorphisms. There were no significantly different allele, genotype or haplotype frequencies between cases or controls. Neither were there any differences when schizophrenic patients were sub-divided with regard to a number of different clinical variables, although a small group of psychotic patients with prominent affective features displayed higher frequencies of the less common alleles of the Val66Met and 11757 G/C polymorphisms compared to controls. The present Swedish results do not verify previous associations between putative functional BDNF gene polymorphisms and schizophrenia. However, when combined with previous studies meta-analyses indicated that the BDNF 270 T-allele and the Val66Met homozygous state were associated with the disorder. Thus, the BDNF gene may confer susceptibility to schizophrenia. Additional studies are warranted to shed further light on this possibility.

Brain derived neurotrophic factor (BDNF) gene variants and Alzheimer's disease, affective disorders, posttraumatic stress disorder, schizophrenia, and substance dependence

Genetic variation at the locus encoding the brain derived neurotrophic factor (BDNF) has been implicated in some neuropsychiatric disorders such as Alzheimer's disease (AD), affective disorders (AFDs), schizophrenia, and substance dependence. We therefore performed a mutation scan of the BDNF gene to identify novel gene variants and examined the association between BDNF variants and several neuropsychiatric phenotypes in European American (EA) subjects and controls. Using denaturing high performance liquid chromatography (dHPLC), we identified a novel variant (G-712A) in the putative promoter region. This variant and two previously reported BDNF SNPs (C270T and Val66Met) were genotyped in 295 patients with AD, 108 with AFDs, 96 with posttraumatic stress disorder (PTSD), 84 with schizophrenia, 327 with alcohol and/or drug dependence, and 250 normal control subjects. No association was found between these three BDNF gene variants and AD, AFDs, PTSD, or schizophrenia. However, there was a nominally higher frequency of the G-712A G-allele and the G/G genotype in subjects with substance dependence than in controls (Allele: chi(2) = 4.080, df = 1, P = 0.043; Genotype: chi(2) = 7.225, df = 2, P = 0.027). Although after correction for multiple testing, the findings are not considered significant (threshold P-value was set at 0.020 by the program SNPSpD), logistic regression analyses confirmed the modest association between SNP G-712A and substance dependence, when the sex and age of subjects were taken into consideration. The negative results for AFDs, PTSD, and schizophrenia could be due to the low statistical power. Further study with larger samples is warranted.

Gene regulation by hypoxia and the neurodevelopmental origin of schizophrenia

Neurodevelopmental changes may underlie the brain dysfunction seen in schizophrenia. While advances have been made in our understanding of the genetics of schizophrenia, little is known about how non-genetic factors interact with genes for schizophrenia. The present analysis of genes potentially associated with schizophrenia is based on the observation that hypoxia prevails in the embryonic and fetal brain, and that interactions between neuronal genes, molecular regulators of hypoxia, such as hypoxia-inducible factor 1 (HIF-1), and intrinsic hypoxia occur in the developing brain and may create the conditions for complex changes in neurodevelopment. Consequently, we searched the literature for currently hypothesized candidate genes for susceptibility to schizophrenia that may be subject to ischemia-hypoxia regulation and/or associated with vascular expression. Genes were considered when at least two independent reports of a significant association with schizophrenia had appeared in the literature. The analysis showed that more than 50% of these genes, particularly AKT1, BDNF, CAPON, CCKAR, CHRNA7, CNR1, COMT, DNTBP1, GAD1, GRM3, IL10, MLC1, NOTCH4, NRG1, NR4A2/NURR1, PRODH, RELN, RGS4, RTN4/NOGO and TNF, are subject to regulation by hypoxia and/or are expressed in the vasculature. Future studies of genes proposed as candidates for susceptibility to schizophrenia should include their possible regulation by physiological or pathological hypoxia during development as well as their potential role in cerebral vascular function.

No association between the brain-derived neurotrophic factor gene and schizophrenia in a Japanese population

Brain-derived neurotrophic factor (BDNF) plays important roles in the survival, maintenance and growth of neurons. Several studies have indicated that BDNF is likely to be related to the pathogenesis of schizophrenia. Recent genetic analyses have revealed that BDNF gene polymorphisms are associated with schizophrenia, although contradictory negative findings have also been reported. To assess whether three BDNF gene polymorphisms (rs988748, C132T and rs6265) could be implicated in vulnerability to schizophrenia, we conducted a case-control association analysis (349 patients and 423 controls) in Japanese subjects. We found no association between these BDNF gene polymorphisms and schizophrenia using both single-marker and haplotype analyses. The results of the present study suggest that these three BDNF gene polymorphisms do not play major roles in conferring susceptibility to schizophrenia in a Japanese population. However, further studies assessing the associations between these BDNF gene polymorphisms and schizophrenia should be performed in several other ethnic populations.

Age at onset of schizophrenia: interaction between brain-derived neurotrophic factor and dopamine D3 receptor gene variants

One of the main features of schizophrenia is its age at onset in early adulthood. Dopaminergic dysregulation is the most documented neurobiological factor that may be involved in triggering schizophrenia. Recent findings on neurodevelopmental processes show that the brain-derived neurotrophic factor plays a critical role in the development of mesolimbic dopaminergic-related systems and regulates the expression of dopamine D3 receptors. In this study, we examine whether an interaction between dopamine D3 receptors and brain-derived neurotrophic factor gene variants influences age at onset in patients with schizophrenia. Our findings show that this gene-gene interaction was significantly associated with an earlier emergence of psychosis by 3 years.