Dysbindin-1 loss compromises NMDAR-dependent synaptic plasticity and contextual fear conditioning

Genetic variants in DTNBP1 encoding the protein dysbindin-1 have often been associated with schizophrenia and with the cognitive deficits prominent in that disorder. Because impaired function of the hippocampus is thought to play a role in these memory deficits and because NMDAR-dependent synaptic plasticity in this region is a proposed biological substrate for some hippocampal-dependent memory functions in schizophrenia, we hypothesized that reduced dysbindin-1 expression would lead to impairments in NMDAR-dependent synaptic plasticity and in contextual fear conditioning. Acute slices from male mice carrying 0, 1, or 2 null mutant alleles of the Dtnbp1 gene were prepared, and field recordings from the CA1 striatum radiatum were obtained before and after tetanization of Schaffer collaterals of CA3 pyramidal cells. Mice homozygous for the null mutation in Dtnbp1 exhibited significantly reduced NMDAR-dependent synaptic potentiation compared to wild type mice, an effect that could be rescued by bath application of the NMDA receptor coagonist glycine (10 μM). Behavioral testing in adult mice revealed deficits in hippocampal memory processes. Homozygous null mice exhibited lower conditional freezing, without a change in the response to shock itself, indicative of a learning and memory deficit. Taken together, these results indicate that a loss of dysbindin-1 impairs hippocampal plasticity which may, in part, explain the role dysbindin-1 plays in the cognitive impairments of schizophrenia.

MeCP2 regulates the synaptic expression of a Dysbindin-BLOC-1 network component in mouse brain and human induced pluripotent stem cell-derived neurons

Clinical, epidemiological, and genetic evidence suggest overlapping pathogenic mechanisms between autism spectrum disorder (ASD) and schizophrenia. We tested this hypothesis by asking if mutations in the ASD gene MECP2 which cause Rett syndrome affect the expression of genes encoding the schizophrenia risk factor dysbindin, a subunit of the biogenesis of lysosome-related organelles complex-1 (BLOC-1), and associated interacting proteins. We measured mRNA and protein levels of key components of a dysbindin interaction network by, quantitative real time PCR and quantitative immunohistochemistry in hippocampal samples of wild-type and Mecp2 mutant mice. In addition, we confirmed results by performing immunohistochemistry of normal human hippocampus and quantitative qRT-PCR of human inducible pluripotent stem cells (iPSCs)-derived human neurons from Rett syndrome patients. We defined the distribution of the BLOC-1 subunit pallidin in human and mouse hippocampus and contrasted this distribution with that of symptomatic Mecp2 mutant mice. Neurons from mutant mice and Rett syndrome patients displayed selectively reduced levels of pallidin transcript. Pallidin immunoreactivity decreased in the hippocampus of symptomatic Mecp2 mutant mice, a feature most prominent at asymmetric synapses as determined by immunoelectron microcopy. Pallidin immunoreactivity decreased concomitantly with reduced BDNF content in the hippocampus of Mecp2 mice. Similarly, BDNF content was reduced in the hippocampus of BLOC-1 deficient mice suggesting that genetic defects in BLOC-1 are upstream of the BDNF phenotype in Mecp2 deficient mice. Our results demonstrate that the ASD-related gene Mecp2 regulates the expression of components belonging to the dysbindin interactome and these molecular differences may contribute to synaptic phenotypes that characterize Mecp2 deficiencies and ASD.

[SNAP-25 and DTNBP1 as candidate genes for cognitive reserve in schizophrenia]

Cognitive reserve (CR) postulates that individual differences in the cognitive processes or neural networks underlying task performance allow some people to cope better than others with brain damage. An aim of the study was to search for candidate genes for CR in schizophrenia. We propose that higher frequencies of low risk alleles is observed in healthy relatives of schizophrenic patients compared to patients and controls and in patients without neurocognitive deficit and with less severity of the disease compared to other patients and controls. Besides, frequencies of these alleles in patients should be similar to those in general population. Authors studied SNAP-25 and DTNBP1 genes. The polymorphism T1065G of SNAP-25 was genotyped in 278 patients with schizophrenia, 126 their relatives and 207 controls and the polymorphism P1763 of DTNBP1 was genotyped in 202 patients, 229 relatives and 262 controls. There was a trend towards the increase in the frequency of an G allele of SNAP-25 in siblings of patients. The frequency of this allele was higher in patients without neurocognitive deficit compared to patients with cognitive deficit (p=0.003) and controls (p=0.002). The allele was associated with index of cognitive functioning in patients (p=0.012) and controls (p=0.006) and with the severity of negative symptoms in patients (p=0.023). At the same time, the polymorphism T1065G was not associated with schizophrenia. Therefore, an allele G may be considered as a marker for higher CR.

The DTNBP1 (dysbindin-1) gene variant rs2619522 is associated with variation of hippocampal and prefrontal grey matter volumes in humans

DTNBP1 is one of the most established susceptibility genes for schizophrenia, and hippocampal volume reduction is one of the major neuropathological findings in this severe disorder. Consistent with these findings, the encoded protein dysbindin-1 has been shown to be diminished in glutamatergic hippocampal neurons in schizophrenic patients. The aim of this study was to investigate the effects of two single nucleotide polymorphisms of DTNBP1 on grey matter volumes in human subjects using voxel-based morphometry. Seventy-two subjects were included and genotyped with respect to two single nucleotide polymorphisms of DTNBP1 (rs2619522 and rs1018381). All participants underwent structural magnetic resonance imaging (MRI). MRI data were preprocessed and statistically analysed using standard procedures as implemented in SPM5 (Statistical Parametric Mapping), in particular the voxel-based morphometry (VBM) toolbox. We found significant effects of the DTNBP1 SNP rs2619522 bilaterally in the hippocampus as well as in the anterior middle frontal gyrus and the intraparietal cortex. Carriers of the G allele showed significantly higher grey matter volumes in these brain regions than T/T homozygotes. Compatible with previous findings on a role of dysbindin in hippocampal functions as well as in major psychoses, the present study provides first direct in vivo evidence that the DTNBP1 SNP rs2619522 is associated with variation of grey matter volumes bilaterally in the hippocampus.

Loss of dysbindin-1 in mice impairs reward-based operant learning by increasing impulsive and compulsive behavior

The dystrobrevin-binding protein 1 (DTNBP1) gene, which encodes the dysbindin-1 protein, is a potential schizophrenia susceptibility gene. Polymorphisms in the DTNBP1 gene have been associated with altered cognitive abilities. In the present study, dysbindin-1 null mutant (dys-/-), heterozygous (dys+/-), and wild-type (dys+/+) mice, on a C57BL/6J genetic background, were tested in either a match to sample or nonmatch to sample visual discrimination task. This visual discrimination task was designed to measure rule learning and detect any changes in response timing over the course of testing. Dys-/- mice displayed significant learning deficits and required more trials to acquire this task. However, once criterion was reached, there were no differences between the genotypes on any behavioral measures. Dys-/- mice exhibited increased compulsive and impulsive behaviors compared to control littermates suggesting the inability to suppress incorrectly-timed responses underlies their increased time to acquisition. Indeed, group comparisons of behavior differences between the first and last day of testing showed that only dys-/- mice consistently decreased measures of perseverative, premature, timeout, and total responses. These findings illustrate how some aspects of altered cognitive performance in dys-/- mice might be related to increased impulsive and compulsive behaviors, analogous to cognitive deficits in some individuals with psychiatric disorders.

The schizophrenia susceptibility factor dysbindin and its associated complex sort cargoes from cell bodies to the synapse

Dysbindin assembles into the biogenesis of lysosome-related organelles complex 1 (BLOC-1), which interacts with the adaptor protein complex 3 (AP-3), mediating a common endosome-trafficking route. Deficiencies in AP-3 and BLOC-1 affect synaptic vesicle composition. However, whether AP-3-BLOC-1-dependent sorting events that control synapse membrane protein content take place in cell bodies upstream of nerve terminals remains unknown. We tested this hypothesis by analyzing the targeting of phosphatidylinositol-4-kinase type II α (PI4KIIα), a membrane protein present in presynaptic and postsynaptic compartments. PI4KIIα copurified with BLOC-1 and AP-3 in neuronal cells. These interactions translated into a decreased PI4KIIα content in the dentate gyrus of dysbindin-null BLOC-1 deficiency and AP-3-null mice. Reduction of PI4KIIα in the dentate reflects a failure to traffic from the cell body. PI4KIIα was targeted to processes in wild-type primary cultured cortical neurons and PC12 cells but failed to reach neurites in cells lacking either AP-3 or BLOC-1. Similarly, disruption of an AP-3-sorting motif in PI4KIIα impaired its sorting into processes of PC12 and primary cultured cortical neuronal cells. Our findings indicate a novel vesicle transport mechanism requiring BLOC-1 and AP-3 complexes for cargo sorting from neuronal cell bodies to neurites and nerve terminals.

Dysbindin-1 mutant mice implicate reduced fast-phasic inhibition as a final common disease mechanism in schizophrenia

DTNBP1 (dystrobrevin binding protein 1) is a leading candidate susceptibility gene in schizophrenia and is associated with working memory capacity in normal subjects. In schizophrenia, the encoded protein dystrobrevin-binding protein 1 (dysbindin-1) is often reduced in excitatory cortical limbic synapses. We found that reduced dysbindin-1 in mice yielded deficits in auditory-evoked response adaptation, prepulse inhibition of startle, and evoked γ-activity, similar to patterns in schizophrenia. In contrast to the role of dysbindin-1 in glutamatergic transmission, γ-band abnormalities in schizophrenia are most often attributed to disrupted inhibition and reductions in parvalbumin-positive interneuron (PV cell) activity. To determine the mechanism underlying electrophysiological deficits related to reduced dysbindin-1 and the potential role of PV cells, we examined PV cell immunoreactivity and measured changes in net circuit activity using voltage-sensitive dye imaging. The dominant circuit impact of reduced dysbindin-1 was impaired inhibition, and PV cell immunoreactivity was reduced. Thus, this model provides a link between a validated candidate gene and an auditory endophenotypes. Furthermore, these data implicate reduced fast-phasic inhibition as a common underlying mechanism of schizophrenia-associated intermediate phenotypes.

Convergence of two independent mental disease genes on the protein level: recruitment of dysbindin to cell-invasive disrupted-in-schizophrenia 1 aggresomes

BACKGROUND

Both disrupted-in-schizophrenia 1 (DISC1) and dysbindin have been identified as schizophrenia candidate genes in independent genetic linkage studies. The proteins have been assigned distinct subcellular locations and functions. We investigated whether both proteins converge into a common pathway specific for schizophrenia or mental diseases.

METHODS

DISC1 and dysbindin were expressed as recombinant proteins with or without a fluorescent protein-tag in human or mouse neuroblastoma cells and as recombinant proteins in E. coli. Postmortem brains of patients with mental diseases from the Stanley Research Medical Institute's Consortium Collection were used to demonstrate molecular interactions in biochemically purified protein fractions.

RESULTS

First, upon overexpression in neuroblastoma cells, DISC1 formed aggresomes that recruited homologous soluble C-terminal DISC1 fragment or heterologous dysbindin. Domains involved in binding could be mapped to DISC1 (316-597) and dysbindin (82-173), indicating a specific interaction. In addition, recruitment was demonstrated when externally added, purified DISC1 aggresomes penetrated recipient cells after coincubation. Second, a direct interaction between soluble DISC1 protein and dysbindin was demonstrated in a cell free system using E. coli-expressed proteins. Third, co-aggregation of DISC1 and dysbindin was demonstrated in postmortem brains for a subgroup of cases with chronic mental disease but not healthy control subjects.

CONCLUSIONS

A direct interaction of soluble and insoluble DISC1 protein with dysbindin protein demonstrates convergence of so far considered independent mental disease genes by direct molecular interaction. Our findings highlight protein aggregation and recruitment as a biological mechanism in mental disease.

Dystrobrevin-binding protein 1 gene (DTNBP1) variants associated with cerebrospinal fluid homovanillic acid and 5-hydroxyindoleacetic acid concentrations in healthy volunteers

The dystrobrevin binding protein-1 (DTNBP1) gene encodes dysbindin-1, a protein involved in neurodevelopmental and neurochemical processes related mainly to the monoamine dopamine. We investigated possible associations between eleven DTNBP1 polymorphisms and cerebrospinal fluid (CSF) concentrations of the major dopamine metabolite homovanillic acid (HVA), the major serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA), and the major noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) in healthy human subjects (n=132). Two polymorphisms, rs2619538 and rs760666, were nominally associated with CSF HVA and 5-HIAA concentrations, whereas a third polymorphism, rs909706, showed association only with HVA. After correction for multiple testing only the associations between rs2619538 and HVA and 5-HIAA concentrations remained significant. No significant association was found between any of the investigated DTNBP1 polymorphisms and CSF MHPG concentrations. The results suggest that genetic variation in DTNBP1 gene affects the regulation of dopamine and serotonin turnover in the central nervous system of healthy volunteers.

The genetics of cognitive ability and cognitive ageing in healthy older people

Determining the genetic influences on cognitive ability in old age and in cognitive ageing are important areas of research in an increasingly ageing society. Heritability studies indicate that genetic variants strongly influence cognitive ability differences throughout the lifespan, including in old age. To date, however, only the genes encoding apolipoprotein E (APOE) and possibly catechol-O-methyl transferase (COMT), brain-derived neurotrophic factor (BDNF) and dystrobrevin binding protein 1 (DTNBP1) have repeatedly been associated in candidate gene studies with cognitive decline or with cognitive ability in older individuals. Genome-wide association studies have identified further potential loci, but results are tentative. Advances in exome and/or whole-genome sequencing, transcriptomics, proteomics and methylomics hold significant promise for uncovering the genetic underpinnings of cognitive ability and decline in old age.

Dysbindin-containing complexes and their proposed functions in brain: from zero to (too) many in a decade

Dysbindin (also known as dysbindin-1 or dystrobrevin-binding protein 1) was identified 10 years ago as a ubiquitously expressed protein of unknown function. In the following years, the protein and its encoding gene, DTNBP1, have become the focus of intensive research owing to genetic and histopathological evidence suggesting a potential role in the pathogenesis of schizophrenia. In this review, we discuss published results demonstrating that dysbindin function is required for normal physiology of the mammalian central nervous system. In tissues other than brain and in non-neuronal cell types, the protein has been characterized as a stable component of a multi-subunit complex, named BLOC-1 (biogenesis of lysosome-related organelles complex-1), which has been implicated in intracellular protein trafficking and the biogenesis of specialized organelles of the endosomal-lysosomal system. In the brain, however, dysbindin has been proposed to associate into multiple complexes with alternative binding partners, and to play a surprisingly wide variety of functions including transcriptional regulation, neurite and dendritic spine formation, synaptic vesicle biogenesis and exocytosis, and trafficking of glutamate and dopamine receptors. This puzzling array of molecular and functional properties ascribed to the dysbindin protein from brain underscores the need of further research aimed at ascertaining its biological significance in health and disease.

Correlated alterations in serotonergic and dopaminergic modulations at the hippocampal mossy fiber synapse in mice lacking dysbindin

Dysbindin-1 (dystrobrevin-binding protein 1, DTNBP1) is one of the promising schizophrenia susceptibility genes. Dysbindin protein is abundantly expressed in synaptic regions of the hippocampus, including the terminal field of the mossy fibers, and this hippocampal expression of dysbindin is strongly reduced in patients with schizophrenia. In the present study, we examined the functional role of dysbindin in hippocampal mossy fiber-CA3 synaptic transmission and its modulation using the sandy mouse, a spontaneous mutant with deletion in the dysbindin gene. Electrophysiological recordings were made in hippocampal slices prepared from adult male sandy mice and their wild-type littermates. Basic properties of the mossy fiber synaptic transmission in the mutant mice were generally normal except for slightly reduced frequency facilitation. Serotonin and dopamine, two major neuromodulators implicated in the pathophysiology of schizophrenia, can potentiate mossy fiber synaptic transmission probably via an increase in cAMP levels. Synaptic potentiation induced by serotonin and dopamine was very variable in magnitude in the mutant mice, with some mice showing prominent enhancement as compared with the wild-type mice. In addition, the magnitude of potentiation induced by these monoamines significantly correlated with each other in the mutant mice, indicating that a subpopulation of sandy mice has marked hypersensitivity to both serotonin and dopamine. While direct activation of the cAMP cascade by forskolin induced robust synaptic potentiation in both wild-type and mutant mice, this forskolin-induced potentaition correlated in magnitude with the serotonin-induced potentiation only in the mutant mice, suggesting a possible change in coupling of receptor activation to downstream signaling. These results suggest that the dysbindin deficiency could be an essential genetic factor that causes synaptic hypersensitivity to dopamine and serotonin. The altered monoaminergic modulation at the mossy fiber synapse could be a candidate pathophysiological basis for impairment of hippocampus-dependent brain functions in schizophrenia.

Synaptic dysbindin-1 reductions in schizophrenia occur in an isoform-specific manner indicating their subsynaptic location

BACKGROUND

An increasing number of studies report associations between variation in DTNBP1, a top candidate gene in schizophrenia, and both the clinical symptoms of the disorder and its cognitive deficits. DTNBP1 encodes dysbindin-1, reduced levels of which have been found in synaptic fields of schizophrenia cases. This study determined whether such synaptic reductions are isoform-specific.

METHODOLOGY/PRINCIPAL FINDINGS

Using Western blotting of tissue fractions, we first determined the synaptic localization of the three major dysbindin-1 isoforms (A, B, and C). All three were concentrated in synaptosomes of multiple brain areas, including auditory association cortices in the posterior half of the superior temporal gyrus (pSTG) and the hippocampal formation (HF). Tests on the subsynaptic tissue fractions revealed that each isoform is predominantly, if not exclusively, associated with synaptic vesicles (dysbindin-1B) or with postsynaptic densities (dysbindin-1A and -1C). Using Western blotting on pSTG (n = 15) and HF (n = 15) synaptosomal fractions from schizophrenia cases and their matched controls, we discovered that synaptic dysbindin-1 is reduced in an isoform-specific manner in schizophrenia without changes in levels of synaptophysin or PSD-95. In pSTG, about 92% of the schizophrenia cases displayed synaptic dysbindin-1A reductions averaging 48% (p = 0.0007) without alterations in other dysbindin-1 isoforms. In the HF, by contrast, schizophrenia cases displayed normal levels of synaptic dysbindin-1A, but 67% showed synaptic reductions in dysbindin-1B averaging 33% (p = 0.0256), while 80% showed synaptic reductions in dysbindin-1C averaging 35% (p = 0.0171).

CONCLUSIONS/SIGNIFICANCE

Given the distinctive subsynaptic localization of dysbindin-1A, -1B, and -1C across brain regions, the observed pSTG reductions in dysbindin-1A are postsynaptic and may promote dendritic spine loss with consequent disruption of auditory information processing, while the noted HF reductions in dysbindin-1B and -1C are both presynaptic and postsynaptic and could promote deficits in spatial working memory.

[Possible relationship of the function of dysbindin-1 with the pathophysiology of schizophrenia]

Schizophrenia is a psychiatric disorder with a prevalence of about 1%. Genetic factors are known to be important in the etiology of schizophrenia and several susceptibility genes have been identified in linkage or association studies. Although the pathophysiology is yet to be determined, unusual neurotransmissions such as dopaminergic and glutamatergic systems have been suggested for the mechanism of schizophrenia symptoms. On the other hand, the concept that schizophrenia is a neurite malformation illness has arisen, based on the observations that DISC1 is involved in neuronal development. The gene for dysbindin-1 (DTNBP1) is situated at chromosome 6, the location of one of the most established linkages to schizophrenia. Interestingly, significant haplotypic associations between DTNBP1 and schizophrenia have been found in several studies in independent populations of schizophrenic cases. In addition, reduction of the gene and the protein of dysbindin-1 have been reported in brains from schizophrenic cases. Hence, genetic variations in DTNBP1 might be a major risk factor for schizophrenia. In the present review, we focus on the function of dysbindin-1 and its potential contributions to the pathophysiology of schizophrenia.

Reduced dysbindin expression mediates N-methyl-D-aspartate receptor hypofunction and impaired working memory performance

BACKGROUND

Schizophrenia is a heritable disorder associated with disrupted neural transmission and dysfunction of brain systems involved in higher cognition. The gene encoding dystrobrevin-binding-protein-1 (dysbindin) is a putative candidate gene associated with cognitive impairments, including memory deficits, in both schizophrenia patients and unaffected individuals. The underlying mechanism is thought to be based in changes in glutamatergic and dopaminergic function within the corticostriatal networks known to be critical for schizophrenia. This hypothesis derives support from studies of mice with a null mutation in the dysbindin gene that exhibit memory dysfunction and excitatory neurotransmission abnormalities in prefrontal and hippocampal networks. At a cellular level, dysbindin is thought to mediate presynaptic glutamatergic transmission.

METHODS

We investigated the relationship between glutamate receptor dynamics and memory performance in dysbindin mutant mice. We assessed N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor function in prefrontal cortex pyramidal neurons in vitro with whole-cell recordings, molecular quantitative analyses (reverse transcription-polymerase chain reaction) of the mandatory NMDA receptor subunit NR1, and cognitive function with a spatial working memory task.

RESULTS

Decreases in dysbindin are associated with specific decreases in NMDA-evoked currents in prefrontal pyramidal neurons, as well as decreases in NR1 expression. Furthermore, the degree of NR1 expression correlates with spatial working memory performance, providing a mechanistic explanation for cognitive changes previously associated with dysbindin expression.

CONCLUSIONS

These data show a significant downregulation of NMDA receptors due to dysbindin deficiency and illuminate molecular mechanisms mediating the association between dysbindin insufficiency and cognitive impairments associated with schizophrenia, encouraging study of the dysbindin/NR1 expression association in humans with schizophrenia.

Nucleocytoplasmic shuttling of dysbindin-1, a schizophrenia-related protein, regulates synapsin I expression

Dysbindin-1 is a 50-kDa coiled-coil-containing protein encoded by the gene DTNBP1 (dystrobrevin-binding protein 1), a candidate genetic factor for schizophrenia. Genetic variations in this gene confer a susceptibility to schizophrenia through a decreased expression of dysbindin-1. It was reported that dysbindin-1 regulates the expression of presynaptic proteins and the release of neurotransmitters. However, the precise functions of dysbindin-1 are largely unknown. Here, we show that dysbindin-1 is a novel nucleocytoplasmic shuttling protein and translocated to the nucleus upon treatment with leptomycin B, an inhibitor of exportin-1/CRM1-mediated nuclear export. Dysbindin-1 harbors a functional nuclear export signal necessary for its nuclear export, and the nucleocytoplasmic shuttling of dysbindin-1 affects its regulation of synapsin I expression. In brains of sandy mice, a dysbindin-1-null strain that displays abnormal behaviors related to schizophrenia, the protein and mRNA levels of synapsin I are decreased. These findings demonstrate that the nucleocytoplasmic shuttling of dysbindin-1 regulates synapsin I expression and thus may be involved in the pathogenesis of schizophrenia.

A polymorphism in the dysbindin gene (DTNBP1) associated with multiple psychiatric disorders including schizophrenia

BACKGROUND

A number of studies have found associations between dysbindin (DTNBP1) polymorphisms and schizophrenia. Recently we identified a DTNBP1 SNP (rs9370822) that is strongly associated with schizophrenia. Individuals diagnosed with schizophrenia were nearly three times as likely to carry the CC genotype compared to the AA genotype.

METHODS

To investigate the importance of this SNP in the function of DTNBP1, a number of psychiatric conditions including addictive behaviours and anxiety disorders were analysed for association with rs9370822.

RESULTS

The DTNBP1 polymorphism was significantly associated with post-traumatic stress disorder (PTSD) as well as nicotine and opiate dependence but not alcohol dependence. Individuals suffering PTSD were more than three times as likely to carry the CC genotype compared to the AA genotype. Individuals with nicotine or opiate dependence were more than twice as likely to carry the CC genotype compared to the AA genotype.

CONCLUSIONS

This study provides further support for the importance of DTNBP1 in psychiatric conditions and suggests that there is a common underlying molecular defect involving DTNBP1 that contributes to the development of several anxiety and addictive disorders that are generally recognised as separate clinical conditions. These disorders may actually be different expressions of a single metabolic pathway perturbation. As our participant numbers are limited our observations should be viewed with caution until they are independently replicated.

A reappraisal of the association between Dysbindin (DTNBP1) and schizophrenia in a large combined case-control and family-based sample of German ancestry

BACKGROUND

Dysbindin (DTNBP1) is a widely studied candidate gene for schizophrenia (SCZ); however, inconsistent results across studies triggered skepticism towards the validity of the findings. In this HapMap-based study, we reappraised the association between Dysbindin and SCZ in a large sample of German ethnicity.

METHOD

Six hundred thirty-four cases with DSM-IV SCZ, 776 controls, and 180 parent-offspring trios were genotyped for 38 Dysbindin SNPs. We also studied two phenotypically-defined subsamples: 147 patients with a positive family history of SCZ (FH-SCZ+) and SCZ patients characterized for cognitive performance with Trail-Making Tests A and B (TMT-A: n=219; TMT-B: n=247). Given previous evidence of gene-gene interactions in SCZ involving the COMT gene, we also assessed epistatic interactions between Dysbindin markers and 14 SNPs in COMT.

RESULTS

No association was detected between Dysbindin markers and SCZ, or in the FH-SCZ+ subgroup. Only one marker (rs1047631, previously reported to be part of a risk haplotype), showed a nominally significant association with performance on TMT-A and TMT-B; these findings did not remain significant after correction for multiple comparisons. Similarly, no pair-wise epistatic interactions between Dysbindin and COMT markers remained significant after correction for 504 pair-wise comparisons.

CONCLUSIONS

Our results, based on one of the largest samples of European Caucasians and using narrowly-defined criteria for SCZ, do not support the etiological involvement of Dysbindin markers in SCZ. Larger samples may be needed in order to unravel Dysbindin's possible role in the genetic basis of proposed intermediate phenotypes of SCZ or to detect epistatic interactions.

What have the genomics ever done for the psychoses?

BACKGROUND

Despite the substantial heritability of the psychoses and their genuine public health burden, the applicability of the genomic approach in psychiatry has been strongly questioned or prematurely dismissed.

METHODS

selective review of the recent literature on molecular genetic and genomic approaches to the psychoses including the early output from genome-wide association studies and the genomic analysis of DNA structural variation.

RESULTS

Susceptibility variants at strong candidate genes have been identified including neuregulin, dysbindin, DISC1 and neurexin 1. Rare but highly penetrant copy number variants and new mutations affecting genes involved in neurodevelopment, cell signalling and synaptic function have been described showing some overlapping genetic architecture with other developmental disorders including autism. The de-novo mutations described offer an explanation for the familial sporadic divide and the persistence of schizophrenia in the population. The functional effects of risk variants at the level of cognition and connectivity has been described and recently, ZNF804A has been identified, and the MHC re-identified as risk loci, and it has been shown that at least a third of the variation in liability is due to multiple common risk variants of small effect with a substantial shared genetic liability between schizophrenia and bipolar affective disorder.

CONCLUSIONS

The genomics have done much for the psychoses to date and more is anticipated.

Dysbindin promotes the post-endocytic sorting of G protein-coupled receptors to lysosomes

Background

Dysbindin, a cytoplasmic protein long known to function in the biogenesis of specialized lysosome-related organelles (LROs), has been reported to reduce surface expression of D2 dopamine receptors in neurons. Dysbindin is broadly expressed, and dopamine receptors are members of the large family of G protein-coupled receptors (GPCRs) that function in diverse cell types. Thus we asked if dysbindin regulates receptor number in non-neural cells, and further investigated the cellular basis of this regulation.

Methodology/Principal Findings

We used RNA interference to deplete endogenous dysbindin in HEK293 and HeLa cells, then used immunochemical and biochemical methods to assess expression and endocytic trafficking of epitope-tagged GPCRs. Dysbindin knockdown up-regulated surface expression of D2 receptors compared to D1 receptors, as reported previously in neurons. This regulation was not mediated by a change in D2 receptor endocytosis. Instead, dysbindin knockdown specifically reduced the subsequent trafficking of internalized D2 receptors to lysosomes. This distinct post-endocytic sorting function explained the minimal effect of dysbindin depletion on D1 receptors, which recycle efficiently and traverse the lysosomal pathway to only a small degree. Moreover, dysbindin regulated the delta opioid receptor, a more distantly related GPCR that is also sorted to lysosomes after endocytosis. Dysbindin was not required for lysosomal trafficking of all signaling receptors, however, as its depletion did not detectably affect down-regulation of the EGF receptor tyrosine kinase. Dysbindin co-immunoprecipitated with GASP-1 (or GPRASP-1), a cytoplasmic protein shown previously to modulate lysosomal trafficking of D2 dopamine and delta opioid receptors by direct interaction, and with HRS that is a core component of the conserved ESCRT machinery mediating lysosome biogenesis and sorting.

Conclusions/Significance

These results identify a distinct, and potentially widespread function of dysbindin in promoting the sorting of specific GPCRs to lysosomes after endocytosis.

The schizophrenia susceptibility gene dysbindin controls synaptic homeostasis

The molecular mechanisms that achieve homeostatic stabilization of neural function remain largely unknown. To better understand how neural function is stabilized during development and throughout life, we used an electrophysiology-based forward genetic screen and assessed the function of more than 250 neuronally expressed genes for a role in the homeostatic modulation of synaptic transmission in Drosophila. This screen ruled out the involvement of numerous synaptic proteins and identified a critical function for dysbindin, a gene linked to schizophrenia in humans. We found that dysbindin is required presynaptically for the retrograde, homeostatic modulation of neurotransmission, and functions in a dose-dependent manner downstream or independently of calcium influx. Thus, dysbindin is essential for adaptive neural plasticity and may link altered homeostatic signaling with a complex neurological disease.

Role of dysbindin in dopamine receptor trafficking and cortical GABA function

Dysbindin has been implicated in the pathogenesis of schizophrenia, but little is known about how dysbindin affects neuronal function in the circuitry underlying psychosis and related behaviors. Using a dysbindin knockout line (dys(-/-)) derived from the natural dysbindin mutant Sandy mice, we have explored the role of dysbindin in dopamine signaling and neuronal function in the prefrontal cortex (PFC). Combined cell imaging and biochemical experiments revealed a robust increase in the dopamine receptor D2, but not D1, on cell surface of neurons from dys(-/-) cortex. This was due to an enhanced recycling and insertion, rather than reduced endocytosis, of D2. Disruption of dysbindin gene resulted in a marked decrease in the excitability of fast-spiking (FS) GABAergic interneurons in both PFC and striatum. Dys(-/-) mice also exhibited a decreased inhibitory input to pyramidal neurons in layer V of PFC. The increased D2 signaling in dys(-/-) FS interneurons was associated with a more pronounced increase in neuronal firing in response to D2 agonist, compared to that in wild-type interneurons. Taken together, these results suggest that dysbindin regulates PFC function by facilitating D2-mediated modulation of GABAergic function.

The effect of COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes on hippocampal and lateral ventricular volume in psychosis

BACKGROUND

Morphometric endophenotypes which have been proposed for psychotic disorders include lateral ventricular enlargement and hippocampal volume reductions. Genetic epidemiological studies support an overlap between schizophrenia and bipolar disorder, and COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes have been implicated in the aetiology of both these disorders. This study examined associations between these candidate genes and morphometric endophenotypes for psychosis.

METHOD

A total of 383 subjects (128 patients with psychosis, 194 of their unaffected relatives and 61 healthy controls) from the Maudsley Family Psychosis Study underwent structural magnetic resonance imaging and genotyping. The effect of candidate genes on brain morphometry was examined using linear regression models adjusting for clinical group, age, sex and correlations between members of the same family.

RESULTS

The results showed no evidence of association between variation in COMT genotype and lateral ventricular, and left or right hippocampal volumes. Neither was there any effect of the BDNF, 5-HTTLPR, NRG1 and DTNBP1 genotypes on these regional brain volumes.

CONCLUSIONS

Abnormal hippocampal and lateral ventricular volumes are among the most replicated endophenotypes for psychosis; however, the influences of COMT, BDNF, 5-HTT, NRG1 and DTNBP1 genes on these key brain regions must be very subtle if at all present.

Association of the DTNBP1 genotype with cognition and personality traits in healthy subjects

BACKGROUND

Schizophrenia is a complex disorder with a high heritability. Family members have an increased risk not only for schizophrenia per se but also for schizophrenia spectrum disorders. Impairment of neuropsychological functions found in schizophrenia patients are also frequently observed in their relatives. The dystrobrevin-binding protein 1 (DTNBP1) gene located at chromosome 6p22.3 is one of the most often replicated vulnerability genes for schizophrenia. In addition, this gene has been shown to modulate general cognitive abilities both in healthy subjects and in patients with schizophrenia.

METHOD

In a sample of 521 healthy subjects we investigated an association between the DTNBP1 genotype [single nucleotide polymorphism (SNP) rs1018381], personality traits [using the NEO Five-Factor Inventory (NEO-FFI) and the Schizotypal Personality Questionnaire - Brief Version (SPQ-B)] and cognitive function (estimated IQ, verbal fluency, attention, working memory and executive function).

RESULTS

Significantly lower scores on the SPQ-B (p=0.0005) and the Interpersonal Deficit subscale (p=0.0005) in carriers of the A-risk allele were detected. There were no differences in any of the cognitive variables between groups.

CONCLUSIONS

The results indicate that genetic variation of the DTNBP1 genotype might exert gene-specific modulating effects on schizophrenia endophenotypes at the population level.

Neurobehavioral abnormalities in the dysbindin-1 mutant, sandy, on a C57BL/6J genetic background

Sandy mice have a deletion mutation in the gene encoding dysbindin-1, Dtnbp1, with consequent reduction of the protein in heterozygotes and its loss in homozygotes. The sandy mouse thus serves as an animal model of dysbindin-1 function. As this protein is concentrated in synaptic tissue and affects transmitter release, it may affect neuronal processes that mediate behavior. To investigate the neurobehavioral effects of the Dtnbp1 mutation, we studied littermate sandy and wild-type controls on a C57BL/6J genetic background. The three animal groups were indistinguishable in their external physical characteristics, sensorimotor skills and indices of anxiety-like behaviors. In the open field, however, homozygous animals were hyperactive and appeared to show less habituation to the initially novel environment. In the Morris water maze, homozygous animals displayed clear deficits in spatial learning and memory with marginal deficits in visual association learning. Apart from the last mentioned deficits, these abnormalities are consistent with hippocampal dysfunction and in some cases with elevated dopaminergic transmission via D2 dopamine receptors. As similar deficits in spatial learning and memory have been found in schizophrenia, where decreased dysbindin-1 has been found in the hippocampus, the sandy mouse may also model certain aspects of cognition and behavior relevant to schizophrenia.

Dysbindin-1, a schizophrenia-related protein, functionally interacts with the DNA- dependent protein kinase complex in an isoform-dependent manner

DTNBP1 has been recognized as a schizophrenia susceptible gene, and its protein product, dysbindin-1, is down-regulated in the brains of schizophrenic patients. However, little is known about the physiological role of dysbindin-1 in the central nervous system. We hypothesized that disruption of dysbindin-1 with unidentified proteins could contribute to pathogenesis and the symptoms of schizophrenia. GST pull-down from human neuroblastoma lysates showed an association of dysbindin-1 with the DNA-dependent protein kinase (DNA-PK) complex. The DNA-PK complex interacts only with splice isoforms A and B, but not with C. We found that isoforms A and B localized in nucleus, where the kinase complex exist, whereas the isoform C was found exclusively in cytosol. Furthermore, results of phosphorylation assay suggest that the DNA-PK complex phosphorylated dysbindin-1 isoforms A and B in cells. These observations suggest that DNA-PK regulates the dysbindin-1 isoforms A and B by phosphorylation in nucleus. Isoform C does not contain exons from 1 to 6. Since schizophrenia-related single nucleotide polymorphisms (SNPs) occur in these introns between exon 1 and exon 6, we suggest that these SNPs might affect splicing of DTNBP1, which leads to impairment of the functional interaction between dysbindin-1 and DNA-PK in schizophrenic patients.

[Serotonin receptor (5-HTR2A) and dysbindin (DTNBP1) genes and component process variables of short-term verbal memory in schizophrenia]

An association study of variations in the DTNBP1 (P1763 and P1578) and 5-HTR2A (T102C and A-1438G) genes with short-term verbal memory efficiency and its component process variables was carried out in 405 patients with schizophrenia and 290 healthy controls. All subjects were asked to recall immediately two sets of 10 words. Total recall, List 1 recall, immediate recall or attention span, proactive interference and a number of intrusions were measured. Patients significantly differed from controls by all memory variables. The efficiency of test performance, efficiency of immediate memory, effect of proactive interference as well as number of intrusions were decreased in the group of patients. Both 5-HTR2A polymorphisms were associated with short-term verbal memory efficiency in the combined sample, with the worst performance observed in carriers of homozygous CC (T102C) and GG (A-1438G) genotypes. The significant effect of the P1763 (DTNBP1) marker on the component process variables (proactive interference and intrusions) was found while its effect on the total recall was non-significant. The homozygotes for GG (P1763) had the worst scores. Overall, the data obtained are in line with the conception of DTNBP1 and 5-HTR2A involvement in different component process variables of memory in healthy subjects and patients with schizophrenia.

Impaired long-term memory retention and working memory in sdy mutant mice with a deletion in Dtnbp1, a susceptibility gene for schizophrenia

BACKGROUND

Schizophrenia is a complex genetic disorder caused by multiple genetic and environmental factors. The dystrobrevin-binding protein 1 (DTNBP1: dysbindin-1) gene is a major susceptibility gene for schizophrenia. Genetic variations in DTNBP1 are associated with cognitive functions, general cognitive ability and memory function, and clinical features of patients with schizophrenia including negative symptoms and cognitive decline. Since reduced expression of dysbindin-1 has been observed in postmortem brains of patients with schizophrenia, the sandy (sdy) mouse, which has a deletion in the Dtnbp1 gene and expresses no dysbindin-1 protein, could be an animal model of schizophrenia. To address this issue, we have carried out a comprehensive behavioral analysis of the sdy mouse in this study.

RESULTS

In a rotarod test, sdy mice did not exhibit motor learning whilst the wild type mice did. In a Barnes circular maze test both sdy mice and wild type mice learned to selectively locate the escape hole during the course of the training period and in the probe trial conducted 24 hours after last training. However, sdy mice did not locate the correct hole in the retention probe tests 7 days after the last training trial, whereas wild type mice did, indicating impaired long-term memory retention. A T-maze forced alternation task, a task of working memory, revealed no effect of training in sdy mice despite the obvious effect of training in wild type mice, suggesting a working memory deficit.

CONCLUSION

Sdy mouse showed impaired long-term memory retention and working memory. Since genetic variation in DTNBP1 is associated with both schizophrenia and memory function, and memory function is compromised in patients with schizophrenia, the sdy mouse may represent a useful animal model to investigate the mechanisms of memory dysfunction in the disorder.

Behavioral abnormalities and dopamine reductions in sdy mutant mice with a deletion in Dtnbp1, a susceptibility gene for schizophrenia

Genetic susceptibility plays an important role in the pathogenesis of schizophrenia. Genetic evidence for an association between the dysbindin-1 gene (DTNBP1: dystrobrevin binding protein 1) and schizophrenia has been repeatedly reported in various populations worldwide. Thus, we performed behavioral analyses on homozygous sandy (sdy) mice, which lack dysbindin-1 owing to a deletion in the Dtnbp1 gene. Our results showed that sdy mice were less active and spent less time in the center of an open field apparatus. Consistent with the latter observation, sdy mice also displayed evidence of heightened anxiety-like response and deficits in social interaction. Compared to wild-type mice, sdy mice displayed lower levels of dopamine, but not glutamate, in the cerebral cortex, hippocampus, and hypothalamus. These findings indicate that sdy mice display a number of behavioral abnormalities associated with schizophrenia and suggest that these abnormalities may be mediated by reductions in forebrain dopamine transmission.

[Neurodevelopmental disturbance in the pathogenesis of major mental disorders]

Neurodevelopmental disturbance may underlie the pathogenesis of major mental disorders, including autism and schizophrenia, based on evidence in epidemiology, clinical psychiatry, brain imaging, and neuropathology. This notion is further supported by the fact that many of genetic susceptibility factors for these disorders have key roles in neurodevelopment. Majority of these genetic factors, such as Neuroligins, SHANK3, Neureglin-1, Dysbindin, and Disrupted-in-Schizophrenia-1 (DISC1) are associated with "synapse." Therefore, "synapse" is one of the most promising sites of convergence in regard to molecular pathways for these mental conditions. In this review, we will summarize the updates of schizophrenia and autism research, with an emphasis on neurodevelopmental disturbances.

Association of schizophrenia with DTNBP1 but not with DAO, DAOA, NRG1 and RGS4 nor their genetic interaction

Recent reports indicate that DAO, DAOA, DTNBP1, NRG1 and RGS4 are some of the most-replicated genes implicated in susceptibility to schizophrenia. Also, the functions of these genes could converge in a common pathway of glutamate metabolism. The aim of this study was to evaluate if each of these genes, or their interaction, was associated with schizophrenia. A case-control study was conducted in 589 Spanish patients having a diagnosis of schizophrenia, and compared with 617 equivalent control subjects. Several single nucleotide polymorphisms (SNPs) in each gene were determined in all individuals. SNP and haplotype frequencies were compared between cases and controls. The interaction between different SNPs at the same, or at different gene, loci was analyzed by the multifactor dimensionality reduction (MDR) method. We found a new schizophrenia risk and protective haplotypes in intron VII of DTNBP1; one of the most important candidate genes for this disorder, to-date. However, no association was found between DAO, DAOA, NRG1 and RGS4 and schizophrenia. The hypothesis that gene-gene interaction in these five genes could increase the risk for the disorder was not confirmed in the present study. In summary, these results may provide further support for an association between the dysbindin gene (DTNBP1) and schizophrenia, but not between the disease and DAO, DAOA, NRG1 and RGS4 or with the interaction of these genes. In the light of recent data, these results need to be interpreted with caution and future analyses with dense genetic maps are awaited.

Early visual processing deficits in dysbindin-associated schizophrenia

BACKGROUND

Variation at the dysbindin gene (DTNBP1) has been associated with increased risk for schizophrenia in numerous independent samples and recently with deficits in general and domain-specific cognitive processing. The relationship between dysbindin risk variants and sensory-level deficits in schizophrenia remains to be explored. We investigated P1 performance, a component of early visual processing on which both patients and their relatives show deficits, in carriers and noncarriers of a known dysbindin risk haplotype.

METHODS

Event-related potential responses to simple visual isolated-check stimuli were measured using high-density electrical scalp recordings in 26 individuals meeting DSM-IV criteria for schizophrenia, comprising 14 patients who were carriers of the dysbindin risk haplotype and 12 patients who were nonrisk haplotype carriers.

RESULTS

Carriers of the dysbindin risk haplotype demonstrated significantly reduced P1 amplitudes compared with noncarriers. A large effect size of d = .89 was calculated for the difference in P1 amplitude over scalp sites where the deficit was maximal.

CONCLUSIONS

The P1 deficits associated with a dysbindin risk haplotype previously identified in our sample presents functional confirmation of its deleterious effect on brain activity. Building on evidence of dysbindin's role in higher cognitive function, these early visual processing deficits suggest a generalized role for dysbindin in brain function and is likely to be part of the mechanism by which illness susceptibility is mediated.

AKT1 is associated with schizophrenia across multiple symptom dimensions in the Irish study of high density schizophrenia families

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K)-AKT signal transduction pathway is critical to cell growth and survival. In vitro functional studies indicate that the candidate schizophrenia susceptibility gene DTNBP1 influences AKT signaling to promote neuronal viability. The AKT1 gene has also been implicated in schizophrenia by association studies and decreased protein expression in the brains of schizophrenic patients.

METHODS

The association of DTNBP1 in the Irish Study of High Density Schizophrenia Families (ISHDSF) prompted our investigation of AKT1 for association with disease in this sample. Eight single nucleotide polymorphisms spanning AKT1 were analyzed for association with schizophrenia across four definitions of affection and according to Operational Criteria Checklist of Psychotic Illness (OPCRIT) symptom scales. We examined expression of AKT1 messenger RNA from postmortem brain tissue of schizophrenic, bipolar, and control individuals.

RESULTS

No single marker showed significant association, but the risk haplotype previously found over-transmitted to Caucasian schizophrenic patients was significantly under-transmitted in the ISHDSF (.01 < p < .05), across all OPCRIT symptom dimensions. Exploratory haplotype analysis confirmed association with schizophrenia toward the 5' end of AKT1 (.008 < p < .049, uncorrected). We found significantly decreased RNA levels in prefrontal cortex of schizophrenic individuals, consistent with reduced AKT1 protein levels reported in schizophrenic brain.

CONCLUSIONS

The replication of association of AKT1 gene variants in a further Caucasian family sample adds support for involvement of AKT signaling in schizophrenia, perhaps encompassing a broader clinical phenotype that includes mood dysregulation. We show that AKT signaling might be compromised in schizophrenic and bipolar patients via reduced RNA expression of specific AKT isoforms.

[Potential genetic predictors for individual vulnerability to substance dependence]

Development of substance dependence is influenced by multiple factors, e.g. pharmacological effects on mental status, environmental and individual factors. Among them genetic factors were found to have greater affect on substance dependence than expected which inheritance rate was calculated as 0.7 or more. However, more precise information on genetic mechanisms underlying substance dependence is still unknown. In Japan, methamphetamine has been the most popular illicit drug. The JGIDA study for genetic factors of methamphetamine dependence/psychosis started in 2001, and revealed many potential genetic predictors for individual vulnerability to methamphetamine dependence and variation of clinical phenotypes. As to susceptibility to drug dependence, 17 genetic variants were identified. A certain SNP or haplotype of the DTNBP1, GSTM1, GSTP1, glycine transporter-1 gene produce risks and that of serotonin transporter, AKT1 and CYP2D6 gene produce negative risks. As to risks of rapid onset of methamphetamine psychosis, worse prognosis or complication of spontaneous relapse, the dopamine D2 receptors, dopamine transporter, monoamine oxidase-A, catechol-O-methyltransferese, SOD2, NQO2, PICK1 gene were identified. Odds ratios of these positive or negative risks ranged from about 0.2 to 15. These findings must be informative for drug dependence rehabilitation programs and psycho-education of substance dependence.

The dysbindin gene (DTNBP1) is associated with methamphetamine psychosis

BACKGROUND

The dysbindin (DTNBP1 [dystrobrevin-binding protein 1]) gene has repeatedly been shown to be associated with schizophrenia across diverse populations. One study also showed that risk haplotypes were shared with a bipolar disorder subgroup with psychotic episodes, but not with all cases. DTNBP1 may confer susceptibility to psychotic symptoms in various psychiatric disorders besides schizophrenia.

METHODS

Methamphetamine psychosis, the psychotic symptoms of which are close to those observed in schizophrenia, was investigated through a case (n = 197)-control (n = 243) association analyses of DTNBP1.

RESULTS

DTNBP1 showed significant associations with methamphetamine psychosis at polymorphisms of P1635 (rs3213207, p = .00003) and SNPA (rs2619538, p = .049) and the three-locus haplotype of P1655 (rs2619539)-P1635-SNPA (permutation p = .0005). The C-A-A haplotype, which was identical to the protective haplotype previously reported for schizophrenia and psychotic bipolar disorders, was a protective factor (p = .0013, odds ratio [OR] = .62, 95% confidence interval [CI] .51-.77) for methamphetamine psychosis. The C-G-T haplotype was a risk for methamphetamine psychosis (p = .0012, OR = 14.9, 95% CI 3.5-64.2).

CONCLUSIONS

Our genetic evidence suggests that DTNBP1 is involved in psychotic liability not only for schizophrenia but also for other psychotic disorders, including substance-induced psychosis.

Dysbindin (DTNBP1) and the biogenesis of lysosome-related organelles complex 1 (BLOC-1): main and epistatic gene effects are potential contributors to schizophrenia susceptibility

BACKGROUND

The DTNBP1 gene, encoding dysbindin, has been strongly implicated in schizophrenia (SZ) susceptibility by a series of independent genetic association and gene expression studies. Among its known functions, dysbindin is part of a protein complex, termed the biogenesis of lysosome-related organelles complex 1 (BLOC-1), the molecular components of which might be involved in the regulation of vesicular trafficking and dendrite branching.

METHODS

A systematic investigation of the other seven BLOC-1 genes (MUTED, PLDN, CNO, SNAPAP, BLOC1S1, BLOC1S2, and BLOC1S3) for evidence of association with SZ was undertaken in a sample of 373 SZ cases and 812 control subjects. Possible epistasis between combinations of BLOC-1 genes, including DTNBP1, was tested with a novel method of investigating for gene-gene interaction. Quality control measures were incorporated into genotyping strategy, and all results were corrected for multiple testing to prevent false positive results.

RESULTS

We identified significant evidence of association between BLOC1S3 and SZ (odds ratio = 1.45, confidence interval = 1.13-1.86, p = .0028, corrected p = .0389). We also report evidence for epistatic interaction between DTNBP1 and MUTED contributing to SZ in the absence of a significant main effect at MUTED (p = .0009, corrected p = .0252). Single marker and epistasis results remained significant after correction for multiple testing.

CONCLUSIONS

Together these data provide evidence for the involvement of the BLOC-1 protein complex in SZ pathogenesis.

Reduced DTNBP1 (dysbindin-1) mRNA in the hippocampal formation of schizophrenia patients

Genetic and molecular studies indicate that dysbindin-1 plays a role in the pathophysiology of schizophrenia. We examined dysbindin-1 mRNA in the hippocampal formation of patients with schizophrenia and found reduced expression in dentate granule and polymorph cells and in hippocampal field CA3, but not in CA1. Furthermore, there were positive correlations between dysbindin-1 mRNA and expression of synaptic markers known to be reduced in schizophrenia. Our results indicate that previously reported dysbindin-1 protein reductions may be due in part to decreased dysbindin-1 mRNA and that reduced dysbindin-1 may contribute to hippocampal formation synaptic pathology in schizophrenia.

Association study between the dystrobrevin binding protein 1 gene (DTNBP1) and schizophrenia: a meta-analysis

Positional, functional and association studies have strongly implicated the dystrobrevin binding protein 1 gene (DTNBP1) as a promising novel candidate gene for schizophrenia. Since the first association study was reported, there have been many attempts to replicate it. However the results have been mixed and these subsequent studies have produced negative as well as positive results. To reconcile these conflicting findings and to give a comprehensive picture of the relationship of DTNBP1 and schizophrenia, the current meta-analysis combined all published association studies involving nine polymorphisms up to May 2006. The results (12 studies including 3429 cases, 3376 controls and 721 trios) showed that there were five single nucleotide polymorphisms (SNPs) with p values < 0.05, however, sensitivity analyses showed that only one SNP was consistent across all nine studies (four of the five SNPs became non-significant after removal of one study), indicating that one study may cause the association findings for each of these four SNPs. In conclusion, there is only a weak association of one SNP in DTNBP1 with schizophrenia, which is not significant after multiple testing.

Impact of schizophrenia candidate genes on schizotypy and cognitive endophenotypes at the population level

BACKGROUND

Aspects of cognitive function and schizotypy have been proposed as potential endophenotypes for schizophrenia. It is unknown whether the expression of these endophenotypes at the population level is modulated by the genetic variability of candidate susceptibility genes for schizophrenia.

METHODS

We examined the potential impact of 18 single nucleotide polymorphisms (SNPs) within the DTNBP1, NRG1, DAOA/G32, and DAAO genes, on cognition and self-rated schizotypy, in a representative population of 2243 young male military conscripts. Single SNP and haplotype associations were evaluated.

RESULTS

The DTNBP1 SNPs rs2619522 and rs760761 exhibited several single marker associations, the minor alleles being associated with lower attention capacity but also a decrease in positive and paranoid schizotypy scores. The DTNBP1 haplotype load had borderline associations with nonverbal IQ, paranoid schizotypy, and sustained attention. For individual NRG1 polymorphisms, isolated but weak signals of association were noted with sustained attention and working memory but not schizotypy. The risk allele of functional SNP8NRG243177 was associated with reduced spatial working memory capacity. An isolated effect of DAAO haplotype variability was noted on negative and disorganization schizotypy. No convincing association of DAOA/G32 variability was detected.

CONCLUSIONS

The DTNBP1 and, less so, NRG1 and DAAO variants might exert gene-specific modulating effects on schizophrenia endophenotypes at the population level.

Association study of dysbindin gene with clinical and outcome measures in a representative cohort of Italian schizophrenic patients

There is evidence suggesting that Dysbindin (DTNBP1) is a susceptibility gene for schizophrenia in Caucasian, Chinese, and Japanese populations. We sought to determine if dysbindin was associated with schizophrenia and its symptoms in a representative group of schizophrenic patients from a Community-Based Mental Health Service (CMHS) in Verona, Italy. A prevalence cohort of schizophrenic patients (n = 141) was assessed at baseline and then 3 and 6 years later. Eighty patients and 106 healthy controls were genotyped for polymorphisms in dysbindin. We tested if diagnosis, clinical symptoms as measured by the Brief Psychiatric Rating Scale (BPRS), and functioning as measured by the Global Assessment of Functioning Scale (GAF), were associated with the presence of certain dysbindin polymorphisms. Finally, using the longitudinal clinical data, we tested if patients carrying dysbindin high-risk haplotypes had a more unfavorable longitudinal clinical outcome. A trend towards statistical association (P = 0.058) between schizophrenia and rs2619538 was found. Using GENECOUNTING software, we found that rs2619538-P1583 (P = 0.048), P1320-P1757 (P = 0.034), and rs2619538-P1583-P1578 (P = 0.040) haplotypes occurred more often in cases compared to controls before correction for multiple testing. The rs2619538-P1583 haplotype was more likely to be transmitted to subjects with more severe and persistent psychopathology. These preliminary results are compatible with the view that DTNBP1 is a susceptibility factor for schizophrenia, and is associated with worse psychopathology.

Effect of 5-haplotype of dysbindin gene (DTNBP1) polymorphisms for the susceptibility to bipolar I disorder

We investigated a possible association between dysbindin gene (DTNBP1) variants and bipolar I disorder (BID). Five SNPs within DTNBP1 (rs3213207, rs1011313, rs2005976, rs760761, and rs2619522) were genotyped for 151 patients with BID and 478 controls. We observed a significant protective association of the haplotype A-C-G-T-A (all SNPs, P = 0.00016) and particularly G-T-A (the last three SNP, P = 0.00007) within DTNBP1 variants investigated. Single marker and subgroup (e.g., psychotic features, age at onset, family history, etc.) analyses showed no significant association. Although the association was due to a small number of subjects, specific DTNBP1 haplotypes, previously associated with schizophrenia, may be also associated with BID. Adequately powered studies from different ethnicities will be necessary to confirm our findings.

New genes associated with schizophrenia in neurite formation: a review of cell culture experiments

New genes consistently associated with schizophrenia include NRG1, Akt, DISC-1 and dysbindin-1. Since these genes participate in neurotransmission, neuroplasticity and neurodevelopment it has not been easy to elucidate which of these roles are abnormal in patients with schizophrenia. Neurite formation is identified as a crucial stage in development, and it is proposed that a defect in neurite formation originating from abnormally encoded proteins by these new genes could be at least an in vitro marker that reflects the most consistent molecular and neuroanatomical findings in schizophrenia. A systematic review of the literature linking the process of neurite formation to genes with replicated evidence that supported their association with schizophrenia was conducted. In addition, an outline of the process of neurite formation was included. Neurite formation was shown to be induced by neuregulins, the product of the gene NRG1. The activation of Akt, a serine/threonine kinase, promoted neurite formation in six independent studies. Conversely, two studies found that Akt inhibits neurite outgrowth. Stronger evidence supporting an association with the new genes related to schizophrenia and neurite formation comes from DISC-1. Defects in DISC-1 protein were shown to directly alter the process of neurite formation. Dysbindin-1 has not yet been directly implicated in neurite outgrowth. These findings suggest that the proteins encoded by NRG1, Akt and DISC-1 are implicated in the process of neurite formation in cellular models as well as, at least in part, animal models during development. Abnormalities in this process could have potential etiologic implications for schizophrenia. Direct evidence, however, of abnormal neurite formation in patients with schizophrenia is still missing. Limitations to this model are identified.

No association evidence between schizophrenia and dystrobrevin-binding protein 1 (DTNBP1) in Taiwanese families

Several linkage studies have shown significant linkage of schizophrenia to chromosome 6p region, which includes the positional candidate genes, Dystrobrevin-binding protein 1 (DTNBP1). The aim was to examine the association evidence of the candidate gene in 693 Taiwanese families with at least two affected siblings of schizophrenia. We genotyped nine SNPs of this gene with average intermarker distance of 17 kb. Intermarker linkage disequilibrium was calculated with GOLD. Single locus and haplotype association analyses were performed with TRANSMIT program. We found no significant association between schizophrenia and DTNBP1 either through single locus or haplotype analyses. We failed to replicate the association evidence between DTNBP1 and schizophrenia and this gene may not play a major role in the etiology of schizophrenia in this Taiwanese family sample.

The genetic deconstruction of psychosis

Psychiatric research, including the search for predisposing genes, has tended to proceed under the assumptions that schizophrenia and bipolar disorder, as defined in Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, and International Statistical Classification of Diseases, 10th Revision, are discrete disease entities with distinct etiology and pathogenesis and that these disease entities can be identified by current "operational" diagnostic conventions. However, recent findings emerging from genetic studies show increasing evidence for an overlap in genetic susceptibility across the traditional binary classification of psychosis. Moreover, the emerging evidence suggests the possibility of relatively specific relationships between genotype and psychopathology. For example, variation in Disrupted in Schizophrenia 1 (DISC1) and Neuregulin 1 (NRG1) may confer susceptibility to a form of illness with mixed features of schizophrenia and mania. The elucidation of genotype-phenotype relationships is at an early stage, but current findings highlight the need to consider alternative approaches to classification and conceptualization for psychiatric research rather than continuing to rely heavily on the traditional categorical approach. We can expect that, over the coming years, molecular genetics will catalyze a reappraisal of psychiatric nosology as well as contribute in a major way to our understanding of pathophysiology and to the development of improved treatments. However, our understanding of the brain mechanisms that link specific gene actions and products to the subjective experience of psychopathological symptoms is likely to be bridged by employing intermediate (or endo-) phenotypes in the domains such as cognition, neurophysiology, or neuroanatomy rather than relying upon clinical measures alone.

RNF151, a testis-specific RING finger protein, interacts with dysbindin

RING finger proteins play important roles in spermatogenesis. Here, we report that a novel RING finger protein RNF151, with a C3HC4-type RING finger domain, a putative nuclear localization signal (NLS), and a TRAF-type zinc finger domain, was exclusively expressed in the mouse testis and developmentally regulated during spermatogenesis. While RNF151 mRNA was present in round spermatids, its protein was expressed in elongating spermatids of the stage VIII-IX seminiferous tubules. The NLS together with the RING domain were necessary and sufficient for the nuclear localization of RNF151-EGFP in transfected cells. Yeast two-hybrid screening identified the physical interaction of mouse RNF151 and dysbindin, which was confirmed by the co-immunoprecipitation of the proteins and by their co-localization in intact cells. As dysbindin has lately been shown to be involved in membrane biogenesis and fusion, a key process for acrosome formation, we propose that RNF151 may play a role in acrosome formation.

High dopamine turnover in the brains of Sandy mice

Schizophrenia is a chronic mental disorder and patients with this disease show positive and negative symptoms, cognitive dysfunction, and deficits in the processing of emotion. From previous studies, dopaminergic neurons are believed to be related to schizophrenic symptoms. Dysbindin (DTNBP1: dystrobrevin binding protein 1) gene is a susceptibility gene for schizophrenia, but the involvement of this gene in the dopaminergic tone remains unknown. In this paper, we studied regional contents of dopamine and its metabolite in the Sandy (Sdy) mouse which expresses no dysbindin protein. The brains of Sdy and wild-type (WT) mice were dissected into ten regions and dopamine (DA) and homovanillic acid (HVA) in each region were determined. DA contents were significantly lower in the cortex, hippocampus, and hypothalamus of Sdy mice than WT mice, while HVA contents showed no differences between the strains. Western blot analysis revealed there were no differences in the amount of tyrosine hydroxylase (TH) in the midbrain (MB) of both strains. The ratios of DA to HVA, which is an index of DA turnover, were higher in the cortex and the hippocampus, but not in the hypothalamus. These data demonstrate that DA turnover in the specific regions of the brain of the Sdy mouse was increased, and the Sdy mouse is a possible useful candidate animal for studying the pathogenic mechanism of schizophrenia.