The DTNBP1 (dysbindin) gene contributes to schizophrenia, depending on family history of the disease

We have investigated the gene for dystrobrevin-binding protein 1 (DTNBP1), or dysbindin, which has been strongly suggested as a positional candidate gene for schizophrenia, in three samples of subjects with schizophrenia and unaffected control subjects of German (418 cases, 285 controls), Polish (294 cases, 113 controls), and Swedish (142 cases, 272 controls) descent. We analyzed five single-nucleotide polymorphisms (P1635, P1325, P1320, P1757, and P1578) and identified significant evidence of association in the Swedish sample but not in those from Germany or Poland. The results in the Swedish sample became even more significant after a separate analysis of those cases with a positive family history of schizophrenia, in whom the five-marker haplotype A-C-A-T-T showed a P value of.00009 (3.1% in controls, 17.8% in cases; OR 6.75; P=.00153 after Bonferroni correction). Our results suggest that genetic variation in the dysbindin gene is particularly involved in the development of schizophrenia in cases with a familial loading of the disease. This would also explain the difficulty of replicating this association in consecutively ascertained case-control samples, which usually comprise only a small proportion of subjects with a family history of disease.     

Genetic variation in the 6p22.3 gene DTNBP1, the human ortholog of the mouse dysbindin gene,is associated with schizophrenia

Prior evidence has supported the existence of multiple susceptibility genes for schizophrenia. Multipoint linkage analysis of the 270 Irish high-density pedigrees that we have studied, as well as results from several other samples, suggest that at least one such gene is located in region 6p24-21. In the present study, family-based association analysis of 36 simple sequence-length-polymorphism markers and of 17 SNP markers implicated two regions, separated by approximately 7 Mb. The first region, and the focus of this report, is 6p22.3. In this region, single-nucleotide polymorphisms within the 140-kb gene DTNBP1 (dystrobrevin-binding protein 1, or dysbindin) are strongly associated with schizophrenia. Uncorrected, empirical P values produced by the program TRANSMIT were significant (P<.01) for a number of individual SNP markers, and most remained significant when the data were restricted to include only one affected offspring per nuclear family per extended pedigree; multiple three-marker haplotypes were highly significant (P=.008-.0001) under the restricted conditions. The pattern of linkage disequilibrium is consistent with the presence of more than one susceptibility allele, but this important issue is unresolved. The number of markers tested in the adjacent genes, all of which are negative, is not sufficient to rule out the possibility that the dysbindin gene is not the actual susceptibility gene, but this possibility appears to be very unlikely. We conclude that further investigation of dysbindin is warranted.     

Association of the DTNBP1 locus with schizophrenia in a U.S. population

Linkage and association studies have recently implicated dystrobrevin-binding protein 1 (DTNBP1) in the etiology of schizophrenia. We analyzed seven previously tested DTNBP1 single-nucleotide polymorphisms (SNPs) in a cohort of 524 individuals with schizophrenia or schizoaffective disorder and 573 control subjects. The minor alleles of three SNPs (P1578, P1763, and P1765) were positively associated with the diagnosis of schizophrenia or schizoaffective disorder in the white subset of the study cohort (258 cases, 467 controls), with P1578 showing the most significant association (odds ratio 1.76, P =.0026). The same three SNPs were also associated in a smaller Hispanic subset (51 cases, 32 controls). No association was observed in the African American subset (215 cases, 74 controls). A stratified analysis of the white and Hispanic subsets showed association with the minor alleles of four SNPs (P1578, P1763, P1320, and P1765). Again, the most significant association was observed for P1578 (P =.0006). Haplotype analysis supported these findings, with a single risk haplotype significantly overrepresented in the white sample (P =.005). Our study provides further evidence for a role of the DTNBP1 gene in the genetic etiology of schizophrenia.     

DTNBP1 (Dystrobrevin binding protein 1) and schizophrenia: association evidence in the 3' end of the gene

OBJECTIVES: Dysbindin (DTNBP1) has been identified as a susceptibility gene for schizophrenia (SZ) through a positional approach. However, a variety of single nucleotide polymorphisms (SNPs) and haplotypes, in different parts of the gene, have been reported to be associated in different samples, and a precise molecular mechanism of disease remains to be defined. We have performed an association study with two well-characterized family samples not previously investigated at the DTNBP1 locus. METHODS: We examined 646 subjects in 136 families with SZ, largely of European ancestry (EA), genotyping 26 SNPs in DTNBP1. RESULTS: Three correlated markers (rs875462, rs760666, and rs7758659) at the 3' region of DTNBP1 showed evidence for association to SZ (p = 0.004), observed in both the EA (p = 0.031) and the African American (AA) subset (p = 0.045) with the same over-transmitted allele. The most significant haplotype in our study was rs7758659-rs3213207 (global p = 0.0015), with rs3213207 being the most frequently reported associated marker in previous studies. A non-conservative missense variant (Pro272Ser) in the 3' region of DTNBP1 that may impair DTNBP1 function was more common in SZ probands (8.2%) than in founders (5%) and in dbSNP (2.1%), but did not reach statistical significance. CONCLUSION: Our results provide evidence for an association of SZ with SNPs at the 3' end of DTNBP1 in the samples studied.     

Simulations of a model for transmitter kinetics

The influence of the internal water balance on the phototactic behaviour in the walking female fly (Calliphora erythrocephala Meig.) was investigated. The phototactic reaction depends on the age of the flies and the duration of water withdrawal. In young blowflies with progressive dehydration, the strength of the light reaction varies considerably from fly to fly. From the 4th. day of life onwards up to day 21 the flies respond much more homogeneously and elicit a reproduceable temporal pattern of reaction (Figs. 2 and 3). All the following statements refer to the behaviour of 10-day-old, virgin females, which, under optimal humidity conditions, have been shown to be spontancously photonegative (Meyer, 1978). The phototactic reaction of progressively dehydrated flies depends in a characteristic manner on the illumination conditions during the intervals between tests. If the flies are kept in darkness during these intervals, the light reaction varies rhythmically, with a period of almost exactly 12 h (Figs. 4a and 5). Under the test conditions this rhythm is found not to vary with the time of day (Fig.4a), or with the length of the between-test intervals, for intervals up to 4h long (Fig. 6). If the flies are kept under illumination during the intervals between tests, the light reaction becomes arhythmical. After an initial maximum after 2–4h of dehydration, further photopositive responses are severely suppressed (Fig. 4b). When the ocelli are covered, the between-test illumination no longer influences the mean response to light. The arhythmic dehydrationtime vs. light-reaction curve in this case is characterised by a strong sustained enhancement of runs towards the light after 10h of dehydration (Fig. 7). A preliminary model of a possible control system for this moisture-dependent phototactic switching is presented, from which all essential results can be deduced. This system determines the phototactic turning direction from the ocelli afferences. These afferences act upon the central nervous system in two ways: directly and also indirectly via the internal water regulation.This work was supported by the DFG-(Me417/4)     

Analysis of a model for transmitter kinetics

Neural transmitters can generally exist in several states: stored, released, in combination with receptors, and recycling to storage. A set of equations is proposed and analyzed for such a system. We have considered boundedness and stability of solutions, and we have discussed physiological effects such as response saturation and adaptation. We have investigated the effects of the model parameters on system behavior and we have indicated how the model can be extended to include phenomena such as transmitter mobilization, modulation if its release and receptor desensitization.     

Neuregulin 1 and susceptibility to schizophrenia

The cause of schizophrenia is unknown, but it has a significant genetic component. Pharmacologic studies, studies of gene expression in man, and studies of mouse mutants suggest involvement of glutamate and dopamine neurotransmitter systems. However, so far, strong association has not been found between schizophrenia and variants of the genes encoding components of these systems. Here, we report the results of a genomewide scan of schizophrenia families in Iceland; these results support previous work, done in five populations, showing that schizophrenia maps to chromosome 8p. Extensive fine-mapping of the 8p locus and haplotype-association analysis, supplemented by a transmission/disequilibrium test, identifies neuregulin 1 (NRG1) as a candidate gene for schizophrenia. NRG1 is expressed at central nervous system synapses and has a clear role in the expression and activation of neurotransmitter receptors, including glutamate receptors. Mutant mice heterozygous for either NRG1 or its receptor, ErbB4, show a behavioral phenotype that overlaps with mouse models for schizophrenia. Furthermore, NRG1 hypomorphs have fewer functional NMDA receptors than wild-type mice. We also demonstrate that the behavioral phenotypes of the NRG1 hypomorphs are partially reversible with clozapine, an atypical antipsychotic drug used to treat schizophrenia.     

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.     

The TRPM7 ion channel functions in cholinergic synaptic vesicles and affects transmitter release

A longstanding hypothesis is that ion channels are present in the membranes of synaptic vesicles and might affect neurotransmitter release. Here we demonstrate that TRPM7, a member of the transient receptor potential (TRP) ion channel family, resides in the membrane of synaptic vesicles of sympathetic neurons, forms molecular complexes with the synaptic vesicle proteins synapsin I and synaptotagmin I, and directly interacts with synaptic vesicular snapin. In sympathetic neurons, changes in TRPM7 levels and channel activity alter acetylcholine release, as measured by EPSP amplitudes and decay times in postsynaptic neurons. TRPM7 affects EPSP quantal size, an intrinsic property of synaptic vesicle release. Targeted peptide interference of TRPM7's interaction with snapin affects the amplitudes and kinetics of postsynaptic EPSPs. Thus, vesicular TRPM7 channel activity is critical to neurotransmitter release in sympathetic neurons.     

The voltage-dependence of transmitter release

In this paper we summarize voltage clamp experiments characterizing transmission at the squid giant synapse. The overall goal of these experiments was to determine a synaptic transfer curve relating presynaptic Ca currents (ICa) to resultant postsynaptic responses. Here we focus on interpreting the phenomenon of transfer curve "hysteresis", which has been proposed to result from an intrinsic voltage-dependence of the transmitter release process. One potential problem in analyzing transfer curves comes from contamination of presynaptic Ca currents by outward currents. Linear leakage currents can be measured and taken into account, but after such corrections ICa measurements at positive potentials are still distorted by outward currents. The presence of residual outward currents at positive potentials results in a voltage-dependent bias in ICa measurement and probably contributes to transfer curve hysteresis. A pharmacological procedure which subtracts currents other than those flowing through Ca channels can be used to circumvent this bias in ICa measurement. Gradients in membrane potential along a nominally voltage clamped presynaptic terminal can allow inappropriate release of transmitter from poorly clamped regions of the terminal. Release from such regions may also contribute to transfer-curve hysteresis when standard voltage clamp methods are employed. A method of localized Ca application which restricts transmitter release to well-clamped presynaptic regions can be used to avoid this problem. Transfer curves measured using refined procedures for ICa measurement and suppression of voltage gradient effects on release exhibit little hysteresis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glutathione S-transferase M1 gene deletion may be associated with susceptibility to certain forms of schizophrenia

Recent studies have revealed that GSTM1 and M2 of the mu-class glutathione S-transferases catalyze a glutathione conjugate of catechol o-quinones including dopachrome, noradrenochrome, and adrenochrome under physiological conditions. Reduced or negative levels of activity amongst these enzymes would lead to an excess of neurotoxic compounds of catecholamine o-quinones. A defect in the mechanisms responsible for this form of detoxification may contribute to the development of certain forms of schizophrenia. We have performed a case-control study to explore the association between schizophrenia and polymorphism of the GSTM1 gene. DNA samples were obtained from 87 unrelated patients with schizophrenia who met the DSM-IV criteria for schizophrenia and from 176 control subjects. Individuals of both groups were ethnically Japanese and were from the same district. GSTM1 polymorphism was determined using the polymerase chain reaction method. The frequency of the GSTM1*0 allele was significantly higher amongst the patients with schizophrenia compared to controls (P = 0.0075). Moreover, the incidence of the GSTM1*0 was significantly higher amongst the schizophrenic patients classified as disorganized type (P = 0.0008), relative to the control sample. Our findings suggest that the GSTM1*0 is associated with an increased susceptibility to schizophrenia, particularly disorganized type of the disease. It is therefore likely that the GSTM1 gene deletion constitutes to vulnerability for disease states of this kind, rather than being the direct cause of schizophrenic conditions.     

Purinergic modulation of transmitter release.

The concept of a purinergic theory for the regulation of the release of neurotransmitters is mainly based on the release of ATP, related nucleotides and adenosine concomitantly with the classical neurotransmitters (Ach and NA) after nerve stimulation, together with the inhibitory effects induced by those substances on the release of those neurotransmitters. As neuromodulators, ATP, related nucleotides and adenosine are in accordance with the classical criteria fulfilled by a neurotransmitter plus the absence of tachyphylaxis to the inhibitory action of purinergic substances, the impossibility to obtain complete blockade of the transmission by using the purinergic compounds and the involvement of Cat²⁺ as a step on the dynamics of the release of neurotransmitters. Furthermore ATP can be responsible for the Wedenski inhibition.     

DISC1: a schizophrenia gene with multiple personalities

Two papers address the contribution of DISC1 to neural development and schizophrenia risk in this issue of?Neuron. These complementary studies elegantly bridge the gap between genetic and cellular studies of?schizophrenia, providing a level of functional validation that is often lacking in the field.     

Analysis of high-resolution HapMap of DTNBP1 (Dysbindin) suggests no consistency between reported common variant associations and schizophrenia

DTNBP1 was first identified as a putative schizophrenia-susceptibility gene in Irish pedigrees, with a report of association to common genetic variation. Several replication studies have reported confirmation of an association to DTNBP1 in independent European samples; however, reported risk alleles and haplotypes appear to differ between studies, and comparison among studies has been confounded because different marker sets were employed by each group. To facilitate evaluation of existing evidence of association and further work, we supplemented the extensive genotype data, available through the International HapMap Project (HapMap), about DTNBP1 by specifically typing all associated single-nucleotide polymorphisms reported in each of the studies of the Centre d'Etude du Polymorphisme Humain (CEPH)-derived HapMap sample (CEU). Using this high-density reference map, we compared the putative disease-associated haplotype from each study and found that the association studies are inconsistent with regard to the identity of the disease-associated haplotype at DTNBP1. Specifically, all five "replication" studies define a positively associated haplotype that is different from the association originally reported. We further demonstrate that, in all six studies, the European-derived populations studied have haplotype patterns and frequencies that are consistent with HapMap CEU samples (and each other). Thus, it is unlikely that population differences are creating the inconsistency of the association studies. Evidence of association is, at present, equivocal and unsatisfactory. The new dense map of the region may be valuable in more-comprehensive follow-up studies.     

GABAA receptor kinetics in the cerebellar nuclei: evidence for detection of transmitter from distant release sites

Neurons of the cerebellar nuclei receive GABAergic input from Purkinje cells. Purkinje boutons have several closely spaced presynaptic densities without GABA transporters, raising the possibility that neurotransmitter released by one presynaptic site diffuses to multiple postsynaptic sites. To test whether such local spillover may contribute to transmission, we studied gating of GABA(A) receptors at 31-33 degrees C in cerebellar nuclear neurons acutely dissociated from mice. Currents were evoked by rapid application of long steps, brief pulses, and high-frequency trains of GABA to outside-out patches. Receptors desensitized and deactivated rapidly, and dose-response measurements estimated an EC(50) of approximately 30 microM. From these data, a kinetic scheme was developed that replicated the recorded currents. Next, we simulated diffusion of GABA in the synaptic cleft, constrained by previous electron microscopic data, and drove the kinetic GABA(A) receptor model with modeled concentration transients. Simulations predicted receptor occupancies of approximately 100% directly opposite the release site and approximately 50% at distant postsynaptic densities, such that receptors up to 700 nm from a release site opened on the timescale of the inhibitory postsynaptic currents before desensitizing. Further simulations of probabilistic release from multiple-site boutons suggested that local spillover-mediated transmission slows the onset and limits the extent of depression during high-frequency signaling.     

Molecular cloning and characterization of human RAI1, a gene associated with schizophrenia

Schizophrenia is a common neuropsychiatric disorder of uncertain etiology that is believed to result from the interaction of environmental factors and multiple genes. To identify new genes predisposing to schizophrenia, numerous groups have focused on CAG-repeat-containing genes. We previously reported a CAG repeat polymorphism that was shown to be associated with both the severity of the phenotype and the response to medication in schizophrenic patients. In this article, we now report the genomic structure of this gene, the retinoic acid inducible-1 gene (RAI1), and present its characterization. This gene, located on chromosome 17p11.2, comprises six exons coding for a 7.6-kb mRNA. The RAI1 gene is highly homologous to its mouse counterpart and it is expressed at high levels mainly in neuronal tissues.     

Chlorpromazine oligomer is a potentially active substance that inhibits human D-amino acid oxidase, product of a susceptibility gene for schizophrenia

D-amino acid oxidase (DAO), a potential risk factor for schizophrenia, has been proposed to be involved in the decreased glutamatergic neurotransmission in schizophrenia. Here we show the inhibitory effect of an antipsychotic drug, chlorpromazine, on human DAO, which is consistent with previous reports using porcine DAO, although human DAO was inhibited to a lesser degree (K(i) = 0.7 mM) than porcine DAO. Since chlorpromazine is known to induce phototoxic or photoallergic reactions and also to be transformed into various metabolites, we examined the effects of white light-irradiated chlorpromazine on the enzymatic activity. Analytical methods including high-resolution mass spectrometry revealed that irradiation triggered the oligomerization of chlorpromazine molecules. The oligomerized chlorpromazine showed a mixed type inhibition with inhibition constants of low micromolar range, indicative of enhanced inhibition. Taken together, these results suggest that oligomerized chlorpromazine could act as an active substance that might contribute to the therapeutic effects of this drug.