An update on the genetics of schizophrenia

Keeping Excitation-Inhibition Ratio in Balance

Unrelated genetic mutations can lead to convergent manifestations of neurological disorders with similar behavioral phenotypes. Experimental data frequently show a lack of dramatic changes in neuroanatomy, indicating that the key cause of symptoms might arise from impairment in the communication between neurons. A transient imbalance between excitatory (glutamatergic) and inhibitory (GABAergic) synaptic transmission (the E/I balance) during early development is generally considered to underlie the development of several neurological disorders in adults. However, the E/I ratio is a multidimensional variable. Synaptic contacts are highly dynamic and the actual strength of synaptic projections is determined from the balance between synaptogenesis and synaptic elimination. During development, relatively slow postsynaptic receptors are replaced by fast ones that allow for fast stimulus-locked excitation/inhibition. Using the binomial model of synaptic transmission allows for the reassessing of experimental data from different mouse models, showing that a transient E/I shift is frequently counterbalanced by additional pre- and/or postsynaptic changes. Such changes—for instance, the slowing down of postsynaptic currents by means of immature postsynaptic receptors—stabilize the average synaptic strength, but impair the timing of information flow. Compensatory processes and/or astrocytic signaling may represent possible targets for medical treatments of different disorders directed to rescue the proper information processing.

Abnormalities in the copper transporter CTR1 in postmortem hippocampus in schizophrenia: A subregion and laminar analysis

Dysbindin-1 modulates copper transport, which is crucial for cellular homeostasis. Several brain regions implicated in schizophrenia exhibit decreased levels of dysbindin-1, which may affect copper homeostasis therein. Our recent study showed decreased levels of dysbindin-1, the copper transporter-1 (CTR1) and copper in the substantia nigra in schizophrenia, providing the first evidence of disrupted copper transport in schizophrenia. In the present study, we hypothesized that there would be lower levels of dysbindin-1 and CTR1 in the hippocampus in schizophrenia versus a comparison group. Using semi-quantitative immunohistochemistry for dysbindin1 and CTR1, we measured the optical density in a layer specific fashion in the hippocampus and entorhinal cortex in ten subjects with schizophrenia and ten comparison subjects. Both regions were richly immunolabeled for CTR1 and dysbindin1 in both groups. In the superficial layers of the entorhinal cortex, CTR1 immunolabeled neuropil and cells showed lower optical density values in patients versus the comparison group. In the molecular layer of the dentate gyrus, patients had higher optical density values of CTR1 versus the comparison group. The density and distribution of dysbindin-1 immunolabeling was similar between groups. These laminar specific alterations of CTR1 in schizophrenia suggest abnormal copper transport in those locations.

Neuregulins in Neurodegenerative Diseases

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), are typically characterized by progressive neuronal loss and neurological dysfunctions in the nervous system, affecting both memory and motor functions. Neuregulins (NRGs) belong to the epidermal growth factor (EGF)-like family of extracellular ligands and they play an important role in the development, maintenance, and repair of both the central nervous system (CNS) and peripheral nervous system (PNS) through the ErbB signaling pathway. They also regulate multiple intercellular signal transduction and participate in a wide range of biological processes, such as differentiation, migration, and myelination. In this review article, we summarized research on the changes and roles of NRGs in neurodegenerative diseases, especially in AD. We elaborated on the structural features of each NRG subtype and roles of NRG/ErbB signaling networks in neurodegenerative diseases. We also discussed the therapeutic potential of NRGs in the symptom remission of neurodegenerative diseases, which may offer hope for advancing related treatment.

Lithium for schizophrenia: supporting evidence from a 12-year, nationwide health insurance database and from Akt1-deficient mouse and cellular models

Accumulating evidence suggests AKT1 and DRD2-AKT-GSK3 signaling involvement in schizophrenia. AKT1 activity is also required for lithium, a GSK3 inhibitor, to modulate mood-related behaviors. Notably, GSK3 inhibitor significantly alleviates behavioral deficits in Akt1^−/− female mice, whereas typical/atypical antipsychotics have no effect. In agreement with adjunctive therapy with lithium in treating schizophrenia, our data mining indicated that the average utilization rates of lithium in the Taiwan National Health Insurance Research Database from 2002 to 2013 are 10.9% and 6.63% in inpatients and outpatients with schizophrenia, respectively. Given that lithium is commonly used in clinical practice, it is of great interest to evaluate the effect of lithium on alleviating Akt1-related deficits. Taking advantage of Akt1^+/− mice to mimic genetic deficiency in patients, behavioral impairments were replicated in female Akt1^+/− mice but were alleviated by subchronic lithium treatment for 13 days. Lithium also effectively alleviated the observed reduction in phosphorylated GSK3α/β expression in the brains of Akt1^+/− mice. Furthermore, inhibition of Akt expression using an Akt1/2 inhibitor significantly reduced neurite length in P19 cells and primary hippocampal cell cultures, which was also ameliorated by lithium. Collectively, our findings implied the therapeutic potential of lithium and the importance of the AKT1-GSK3 signaling pathway.

From Schizophrenia Genetics to Disease Biology: Harnessing New Concepts and Technologies

Schizophrenia (SZ) is a severe mental disorder afflicting around 1% of the population. It is highly heritable but with complex genetics. Recent research has unraveled a plethora of risk loci for SZ. Accordingly, our conceptual understanding of SZ genetics has been rapidly evolving, from oligogenic models towards polygenic or even omnigenic models. A pressing challenge to the field, however, is the translation of the many genetic findings of SZ into disease biology insights leading to more effective treatments. Bridging this gap requires the integration of genetic findings and functional genomics using appropriate cellular models. Harnessing new technologies, such as the development of human induced pluripotent stem cells (hiPSC) and the CRISPR/Cas-based genome/epigenome editing approach are expected to change our understanding of SZ disease biology to a fundamentally higher level. Here, we discuss some new developments.

Current developments in the genetics of Rett and Rett-like syndrome

PURPOSE OF REVIEW

This article reviews the current molecular genetic studies, which investigate the genetic causes of Rett syndrome or Rett-like phenotypes without a MECP2 mutation.

RECENT FINDINGS

As next generation sequencing becomes broadly available, especially whole exome sequencing is used in clinical diagnosis of the genetic causes of a wide spectrum of intellectual disability, autism, and encephalopathies. Patients who were diagnosed with Rett syndrome or Rett-like syndrome because of their phenotype but were negative for mutations in the MECP2, CDKL5 or FOXG1 genes were subjected to whole exome sequencing and the results of the last few years revealed yet 69 different genes. Many of these genes are involved in epigenetic gene regulation, chromatin shaping, neurotransmitter action or RNA transcription/translation. Genetic data also allows to investigate the individual genetic background of an individual patient, which can modify the severity of a genetic disorder.

SUMMARY

We conclude that the Rett syndrome phenotype has a much broader underlying genetic cause and the typical phenotype overlap with other genetic disorders. For proper genetic counselling, patient perspective and treatment it is important to include both phenotype and genetic information.

Physiological and pathological roles of exosomes in the nervous system

Exosomes represent a subtype of extracellular nanovesicles that are generated from the luminal budding of limiting endosomal membranes and subsequent exocytosis. They encapsulate or associate with obsolete molecules to eliminate or to transfer their cargos in intercellular communication. The exosomes are also released and transported between neurons and glia in the nervous system, having a broad impact on nerve development, activation and regeneration. Accumulating evidence suggests that the exosomes are attributed to the pathogenesis of several neurodegenerative diseases such as prion disease, Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, as well as aging, in which the exosomes lack the capacity for cellular self-repair and spread their enclosed pathological agents among neurons. In this article, we review the current proposed functions of exosomes in physiological and pathological processes in the nervous system.

Akting up in the GABA hypothesis of schizophrenia: Akt1 deficiency modulates GABAergic functions and hippocampus-dependent functions

Accumulating evidence implies that both AKT1 and GABA_A receptor (GABA_AR) subunit genes are involved in schizophrenia pathogenesis. Activated Akt promotes GABAergic neuron differentiation and increases GABA_AR expression on the plasma membrane. To elucidate the role of Akt1 in modulating GABAergic functions and schizophrenia-related cognitive deficits, a set of 6 in vitro and in vivo experiments was conducted. First, an Akt1/2 inhibitor was applied to evaluate its effect on GABAergic neuron-like cell formation from P19 cells. Inhibiting Akt resulted in a reduction in parvalbumin-positive neuron-like cells. In Akt1^−/− and wild-type mice, seizures induced using pentylenetetrazol (a GABA_AR antagonist) were measured, and GABA_AR expression and GABAergic interneuron abundance in the brain were examined. Female Akt1^−/− mice, but not male Akt1^−/− mice, exhibited less pentylenetetrazol-induced convulsive activity than their corresponding wild-type controls. Reduced parvalbumin-positive interneuron abundance and GABA_AR subunit expression, especially in the hippocampus, were also observed in female Akt1^−/− mice compared to female wild-type mice. Neuromorphometric analyses revealed significantly reduced neurite complexity in hippocampal pyramidal neurons. Additionally, female Akt1^−/− mice displayed increased hippocampal oscillation power and impaired spatial memory compared to female wild-type mice. Our findings suggest that Akt1 deficiency modulates GABAergic interneurons and GABA_AR expression, contributing to hippocampus-dependent cognitive functional impairment.

Striatal dopamine release in a schizophrenia mouse model measured by electrochemical amperometry in vivo

Schizophrenia is a severely devastating mental disorder, the pathological process of which is proposed to be associated with the dysfunction of dopaminergic transmission. Our previous results have demonstrated slower kinetics of transmitter release (glutamate release in hippocampus and norepinephrine release in adrenal slice) in a schizophrenia model, dysbindin null-sandy mice. However, whether dopaminergic transmission in the nigrostriatal pathway contributes to the pathology of dysbindin-/- mice remains unknown. Here, we have provided a step-by-step protocol to be applied in the in vivo amperometric recording of dopamine (DA) release from the mouse striatum evoked by an action potential (AP) pattern. With this protocol, AP pattern-dependent DA release was recorded from dysbindin-/- mice striatum in vivo. On combining amperometric recording in slices and electrophysiology, we found that in dysbindin-/- mice, (1) presynaptically, AP-pattern dependent dopamine overflow and uptake were intact in vivo; (2) the recycling of the dopamine vesicle pool remained unchanged. (3) Postsynaptically, the excitability of medium spiny neuron (MSN) was also normal, as revealed by patch-clamp recordings in striatal slices. Taken together, in contrast to reduced norepinephrine release in adrenal chromaffin cells, the dopaminergic transmission remains unchanged in the nigrostriatal pathway in dysbindin-/- mice, providing a new insight into the functions of the schizophrenia susceptibility gene dysbindin.

Investigation of gene effects and epistatic interactions between Akt1 and neuregulin 1 in the regulation of behavioral phenotypes and social functions in genetic mouse models of schizophrenia

Accumulating evidence from human genetic studies has suggested several functional candidate genes that might contribute to susceptibility to schizophrenia, including AKT1 and neuregulin 1 (NRG1). Recent findings also revealed that NRG1 stimulates the PI3-kinase/AKT signaling pathway, which might be involved in the functional outcomes of some schizophrenic patients. The aim of this study was to evaluate the effect of Akt1-deficiency and Nrg1-deficiency alone or in combination in the regulation of behavioral phenotypes, cognition, and social functions using genetically modified mice as a model. Male Akt1^+/−, Nrg1^+/−, and double mutant mice were bred and compared with their wild-type (WT) littermate controls. In Experiment 1, general physical examination revealed that all mutant mice displayed a normal profile of body weight during development and a normal brain activity with microPET scan. In Experiment 2, no significant genotypic differences were found in our basic behavioral phenotyping, including locomotion, anxiety-like behavior, and sensorimotor gating function. However, both Nrg1^+/− and double mutant mice exhibited impaired episodic-like memory. Double mutant mice also had impaired sociability. In Experiment 3, a synergistic epistasis between Akt1 and Nrg1 was further confirmed in double mutant mice in that they had impaired social interaction compared to the other 3 groups, especially encountering with a novel male or an ovariectomized female. Double mutant and Nrg1^+/− mice also emitted fewer female urine-induced ultrasonic vocalization calls. Collectively, our results indicate that double deficiency of Akt1 and Nrg1 can result in the impairment of social cognitive functions, which might be pertinent to the pathogenesis of schizophrenia-related social cognition.

Signaling mechanisms regulating myelination in the central nervous system

The precise and coordinated production of myelin is essential for proper development and function of the nervous system. Diseases that disrupt myelin, including multiple sclerosis, cause significant functional disability. Current treatment aims to reduce the inflammatory component of the disease, thereby preventing damage resulting from demyelination. However, therapies are not yet available to improve natural repair processes after damage has already occurred. A thorough understanding of the signaling mechanisms that regulate myelin generation will improve our ability to enhance repair. in this review, we summarize the positive and negative regulators of myelination, focusing primarily on central nervous system myelination. Axon-derived signals, extracellular signals from both diffusible factors and the extracellular matrix, and intracellular signaling pathways within myelinating oligodendrocytes are discussed. Much is known about the positive regulators that drive myelination, while less is known about the negative regulators that shift active myelination to myelin maintenance at the appropriate time. Therefore, we also provide new data on potential negative regulators of CNS myelination.

An updated overview of animal models in neuropsychiatry

Animal models are vital tools to study the genetic, molecular, cellular, and environmental parameters involved in several neuropsychiatric disorders. Over the years, these models have expanded our understanding of the pathogenesis of many neuropsychiatric disorders and neurodegenerative diseases. Although animal models have been widely used in psychiatry, and despite several years of extensive research with these models, their validity is still being investigated and presents a challenge to both investigators and clinicians as well. In this concise review, we will describe the most common animal models utilized in neuropsychiatry, including animal models of depression, anxiety, and psychosis. In addition, we will also discuss the validity and reliability of these models and current challenges in this domain. Furthermore, this work will discuss the role of gene-environment interaction as an additional contributing factor that modulates neuropsychological outcome and its implication on animal models. This overview will give a succinct summary of animal models in psychiatry which will be useful both to the seasoned researcher, as well as novices in the field.

Association study between the rs165599 catechol-O-methyltransferase genetic polymorphism and schizophrenia in a Brazilian sample

Schizophrenia is a severe psychiatric disorder with frequent recurrent psychotic relapses and progressive functional impairment. It results from a poorly understood gene-environment interaction. The gene encoding catechol-O-methyltransferase (COMT) is a likely candidate for schizophrenia. Its rs165599 (A/G) polymorphism has been shown to be associated with alteration of COMT gene expression. Therefore, the present study aimed to investigate a possible association between schizophrenia and this polymorphism. The distribution of the alleles and genotypes of this polymorphism was investigated in a Brazilian sample of 245 patients and 834 controls. The genotypic frequencies were in Hardy-Weinberg equilibrium and no statistically significant differences were found between cases and controls when analyzed according to gender or schizophrenia subtypes. There was also no difference in homozygosis between cases and controls. Thus, in the sample studied, there was no evidence of any association between schizophrenia and rs165599 (A/G) polymorphism in the non-coding region 3' of the COMT gene.

Both chronic treatments by epothilone D and fluoxetine increase the short-term memory and differentially alter the mood status of STOP/MAP6 KO mice

Recent evidence underlines the crucial role of neuronal cytoskeleton in the pathophysiology of psychiatric diseases. In this line, the deletion of STOP/MAP6 (Stable Tubule Only Polypeptide), a microtubule-stabilizing protein, triggers various neurotransmission and behavioral defects, suggesting that STOP knockout (KO) mice could be a relevant experimental model for schizoaffective symptoms. To establish the predictive validity of such a mouse line, in which the brain serotonergic tone is dramatically imbalanced, the effects of a chronic fluoxetine treatment on the mood status of STOP KO mice were characterized. Moreover, we determined the impact, on mood, of a chronic treatment by epothilone D, a taxol-like microtubule-stabilizing compound that has previously been shown to improve the synaptic plasticity deficits of STOP KO mice. We demonstrated that chronic fluoxetine was either antidepressive and anxiolytic, or pro-depressive and anxiogenic, depending on the paradigm used to test treated mutant mice. Furthermore, control-treated STOP KO mice exhibited paradoxical behaviors, compared with their clear-cut basal mood status. Paradoxical fluoxetine effects and control-treated STOP KO behaviors could be because of their hyper-reactivity to acute and chronic stress. Interestingly, both epothilone D and fluoxetine chronic treatments improved the short-term memory of STOP KO mice. Such treatments did not affect the serotonin and norepinephrine transporter densities in cerebral areas of mice. Altogether, these data demonstrated that STOP KO mice could represent a useful model to study the relationship between cytoskeleton, mood, and stress, and to test innovative mood treatments, such as microtubule-stabilizing compounds.

Association study of GRIK1 gene polymorphisms in schizophrenia: case-control and family-based studies

Glutamatergic function is one of the major hypotheses for schizophrenia. Within the glutamate system, the glutamate receptor ionotropic kainate-1 (GRIK1) gene is thought to be particularly involved in schizophrenia because of the reported reduction of GRIK1 in the dorsolateral prefrontal cortex of patients.

OBJECTIVE

We examined single-nucleotide polymorphisms (SNPs) in the GRIK1 gene for possible association with schizophrenia.

METHODS

We analyzed eight SNPs across the GRIK1 gene in 202 case-control pairs and 108 small nuclear families.

RESULTS

For the case-control study, we found nominal significant associations in the analysis of rs469472 (p = 0.028) and its haplotypes. In the family-based study, nominal significant association was also observed for rs469472 (p = 0.046), as well as rs455892 (p = 0.024). The marker rs469472 was associated with schizophrenia when we combined the case-control and family samples (p = 0.027). The association findings did not survive correction for multiple testing.

CONCLUSIONS

Because we observed similar association findings with marker rs469472 in two independent samples, further analyses in larger samples are warranted.

Case-control association study for 10 genes in patients with schizophrenia: influence of 5HTR1A variation rs10042486 on schizophrenia and response to antipsychotics

The aim of this study is to investigate possible associations between a set of single-nucleotide polymorphisms (SNPs) within 10 genes with Schizophrenia (SCZ) and response to antipsychotics in Korean in-patients treated with antipsychotics. Two hundred and twenty-one SCZ in-patients and 170 psychiatrically healthy controls were genotyped for 42 SNPs within ABCB1, ABCB4, TAP2, CLOCK, CPLX1, CPLX2, SYN2, NRG1, 5HTR1A and GPRIN2. Baseline and final clinical measures, including the Positive and Negative Symptoms Scale (PANSS), were recorded. Rs10042486 within 5HTR1A was associated with both SCZ and clinical improvement on PANSS total scores as well as on PANSS positive and PANSS negative scores. The haplotype analyses focusing on the four, three and two blocks' haplotypes within 5HTR1A confirmed such findings as well. We did not observe any significant association between the remaining genetic variants under investigation in this study and clinical outcomes. Our preliminary findings suggest that rs10042486 within 5HTR1A promoter region could be associated with SCZ and with clinical improvement on PANSS total, positive and negative scores in Korean patients with SCZ. However, taking into account the several limitations of our study, further research is needed to draw more definitive conclusions.

Influence of GRIA1, GRIA2 and GRIA4 polymorphisms on diagnosis and response to antipsychotic treatment in patients with schizophrenia

The present study is aimed at exploring whether some single nucleotide polymorphisms (SNPs) within GRIA1, GRIA2 and GRIA4 could be associated with schizophrenia and whether they could predict clinical outcomes in Korean in-patients treated with antipsychotics. One hundred forty five patients with MD, 221 in-patients with schizophrenia and 170 psychiatrically healthy controls were genotyped for 17 SNPs within GRIA1, GRIA2 and GRIA4. Baseline and final clinical measures, including the Positive and Negative Symptoms Scale (PANSS), were recorded. No significant association was found with the diagnosis of schizophrenia. We observed an association between rs3813296 genotype and improvement on PANSS negative scores. Our findings provide no evidence for an association between SNPs within GRIA1, GRIA2 and GRIA4 under investigation and schizophrenia susceptibility, although rs3813296 (GRIA2) could be associated with improvement on PANSS negative scores. However, taking into account the several limitations of our study, further research is needed to draw more definitive conclusions.

Genetic association studies of antioxidant pathway genes and schizophrenia

The endogenous production of highly reactive oxidation species is an inherent by-product of cellular energy metabolism. Cellular antioxidant defense systems (AODS) comprising various antioxidants counter these damaging effects. Several lines of evidence, including postmortem studies, suggest increased oxidative stress in patients with schizophrenia. Some genetic association studies and gene-expression studies suggest that patients also may have altered ability to mount antioxidative mechanisms. As the genetic associations may provide etiologic evidence in support of the oxidative-stress hypothesis of schizophrenia, a focused review has been conducted. We also suggest avenues for further research.

Pharmacogenetic approaches to cognitive enhancement in schizophrenia

Research in the area of pharmacogenetics in psychiatry is aimed at identifying clinically relevant genetic variations that can predict treatment response. Ultimately, the goal is to individualize treatment in order to optimize outcome in disorders in which incomplete treatment response is common. Positive symptoms in patients with schizophrenia appear to be the most amenable to the currently available agents; however, negative symptoms and cognitive deficits frequently persist even when frank psychosis is well controlled. Given the relationship between these persistent traits and functional disability in schizophrenia, efforts are under way to directly target cognitive impairment and negative symptoms pharmacologically in order to improve quality of life. To date, most pharmacogenetic studies of schizophrenia have been focused on predicting clinical efficacy and side effects. In this review, we discuss the potential use of cognition as a primary outcome measure of interest in future pharmacogenetic trials of schizophrenia.

The contribution of epidemiology to defining the most appropriate approach to genetic research on schizophrenia

Psychosis is thought to have a strong genetic component, but many efforts to discover the underlying putative schizophrenia genes have yielded disappointing results. In fact, no strong associations emerged in the first genome-wide association studies in psychiatry and weakly observed associations were not related to the candidate genes identified in previous studies. These partially successful findings may be explained by the fact that genetic research in psychiatry suffers from confounding issues related to phenotype definition, the considerable degree of phenotypic variability and diagnostic uncertainty, absence of specific neuropathological features and environmental influences. To make progress it is first necessary to deconstruct psychosis based on symptomatology, and then to correlate particular phenotypes with genetic variants. Moreover, it is time to conduct studies that define persistent aspects of the schizophrenic profile that are more likely to represent an underlying biological pathogenesis, as opposed to fluctuating symptoms that are possibly environmentally mediated. In fact, progress in understanding the etiology of schizophrenia will depend upon the availability of good measures of genetic liability as well as relevant environmental exposures during critical periods of an individual's life. If environmental and/or genetic factors are not precisely measured, it is impossible to study their independent effects or interactions.

Dissecting the many genetic faces of schizophrenia

Recent genome-wide association studies in schizophrenia have provided strongest evidence for association and this strengthened when the affected phenotype included bipolar disorder suggesting that genes may not always associate with operationalised diagnostic entities. Several further large Genome Wide Association (GWA) studies on schizophrenia are under way and identified and replicated further loci in well-powered cohorts. The last 2 years have also witnessed an explosion of interest in human Copy Number Variants (CNVs). Deletions recently identified in schizophrenia (1q21.1; 2p16.3; 15q11.2; 15q13.3) have also been most recently found in further neurodevelopmental diseases. Thus, a significant fraction of individuals with neurodevelopmental diseases including schizophrenia carry CNVs and many will be defined as “genomic disorders” in the coming years. These findings could represent a decisive step towards understanding the causes of this severe mental disorder as well as developing new potential treatments. There is new hope that these new avenues will help understanding the neurobiology of schizophrenia in more depth leading to the development of new innovative diagnostic tools and therapies as was the case after the discovery of rare APP and presenilin 1 and 2 mutations in Alzheimer's disease.

Glutamate signaling in the pathophysiology and therapy of schizophrenia

Glutamatergic neurotransmission, particularly through the N-methyl-d-aspartate (NMDA) receptor, has drawn attention for its role in the pathophysiology of schizophrenia. This paper reviews the neurodevelopmental origin and genetic susceptibility of schizophrenia relevant to NMDA neurotransmission, and discusses the relationship between NMDA hypofunction and different domains of symptom in schizophrenia as well as putative treatment modality for the disorder. A series of clinical trials and a meta-analysis which compared currently available NMDA-enhancing agents suggests that glycine, d-serine, and sarcosine are more efficacious than d-cycloserine in improving the overall psychopathology of schizophrenia without side effect or safety concern. In addition, enhancing glutamatergic neurotransmission via activating the AMPA receptor, metabotropic glutamate receptor or inhibition of d-amino acid oxidase (DAO) is also reviewed. More studies are needed to determine the NMDA vulnerability in schizophrenia and to confirm the long-term efficacy, functional outcome, and safety of these NMDA-enhancing agents in schizophrenic patients, particularly those with refractory negative and cognitive symptoms, or serious adverse effects while taking the existing antipsychotic agents.

Developments in schizophrenia genetics: from linkage to microchips, deletions and duplications

BACKGROUND

There is strong evidence for significant contributions of genetic factors to the risk of schizophrenia. In the past 10 years, studies employing linkage and association approaches have identified multiple putative schizophrenia risk genes. For most of these, the evidence for association with schizophrenia remains weak and attempts of replication not always successful nor easy to interpret.

AIM

To give an overview of new developments in genetic research of schizophrenia.

METHODS

The present literature on schizophrenia genetics was reviewed with special emphasis on new developments such as genome-wide association studies (GWAS), associations of copy number variations (CNVs) with schizophrenia and the role of endophenotypes in genetic research.

RESULTS

The first GWAS of schizophrenia have identified new putative candidate risk genes and opened avenues for investigating how multiple genes may act in functional biological pathways forming the genetic basis of schizophrenia and other complex diseases. There is growing evidence that rare de novo CNVs as well as some inherited CNVs contribute to the susceptibility to several neuropsychiatric disorders including schizophrenia. Schizophrenia endophenotypes, which possibly better represent biological phenomena than the complex clinical phenotype, are turning out to be helpful for investigating neurobiological pathways of putative risk genes.

CONCLUSIONS

Recent studies suggest that individual common gene variants make relatively small contributions to risk of schizophrenia but some rare CNVs may be associated with much higher risk when present. Future studies employing new technologies for identifying common and rare risk markers are likely to deepen our understanding of the genetic architecture of schizophrenia.

Association between the SLC6A3 A1343G polymorphism and schizophrenia

Epidemiological studies have demonstrated that the genetic component is an important risk factor for the development of schizophrenia. The genes that codify the different compounds of the dopaminergic system have created interest for molecular investigations in patients with schizophrenia because the antipsychotic drugs, especially those of first generation, act on this cerebral system. Thus the aim of the present study was to investigate the possible association between a new single nucleotide polymorphism (rs6347) located in exon 9 of the protein transporter (SLC6A3) and schizophrenia. The distribution of the alleles and genotypes of the studied polymorphism was investigated in a sample of 235 patients and 834 controls matched by gender and age. There were statistical differences in the allelic (χ²= 5.97, 1d.f. , p = 0.01, OR = 1.33-1.05 < OR < 1.69) and genotypic (χ² = 6.56, 2d.f. , p = 0.03) distributions between patients and controls. Thus the SLC6A3 A1343G polymorphism was associated to the SCZ phenotype in the investigated sample.

Do COMT, BDNF and NRG1 polymorphisms influence P50 sensory gating in psychosis?

BACKGROUND

Auditory P50 sensory gating deficits correlate with genetic risk for schizophrenia and constitute a plausible endophenotype for the disease. The well-supported role of catechol-O-methyltransferase (COMT), brain-derived neurotrophic factor (BDNF) and neuregulin 1 (NRG1) genes in neurodevelopment and cognition make a strong theoretical case for their influence on the P50 endophenotype.

METHOD

The possible role of NRG1, COMT Val158Met and BDNF Val66Met gene polymorphisms on the P50 endophenotype was examined in a large sample consisting of psychotic patients, their unaffected relatives and unrelated healthy controls using linear regression analyses.

RESULTS

Although P50 deficits were present in patients and their unaffected relatives, there was no evidence for an association between NRG1, COMT Val158Met or BDNF Val66Met genotypes and the P50 endophenotype.

CONCLUSIONS

The evidence from our large study suggests that any such association between P50 indices and NRG1, COMT Val158Met or BDNF Val66Met genotypes, if present, must be very subtle.

Toward personalized medicine in the neuropsychiatric field

There are great expectations for the personalized medicine approach to address the therapeutic needs of patients in the twenty-first century. Advances in human genome science and molecular innovations in neuroscience have encouraged the pharmaceutical industry to focus beyond broad spectrum population therapeutics--the driving force behind the "blockbuster" product concept--to personalized medicine. For central nervous system (CNS) therapeutics, repeated failures in converting scientific discoveries to clinical trial successes and regulatory approvals have precipitated a drug pipeline crisis and eroded confidence in the industry. This chapter describes how innovations in genomics and translational medicine can impact the future of neuropsychiatry and deconvolute the complexity of psychiatric diseases from symptoms biology. A targeted and consistent investment is needed to restore confidence in translating science into clinical success.

The importance of systematic genetic approach to familial schizophrenia cases and discussion of cryptic mosaic X chromosome aneuploidies in schizophrenia pathogenesis

Abstract Objective. The aim of this study is to contribute to the understanding of schizophrenia genetics by using efficient algorithmic examination techniques including dysmorphic examination, karyotyping, and Fluoresence in situ hybridization (FISH). Methods. In this study we have investigated 20 familial schizophrenia patients from Turkey who had an affected first-degree relative. Dysmorphic examination of the schizophrenia cases and their relatives have been performed. High resolution banding (HRB), specific centromeric, subtelomeric and 22q11.2 region FISH probes were used for genotyping of patients. Results. Dysmorphic examination revealed ear, palate, nose, columella anomalies, and obesity in contributing patients, and the pale skin was noticed. The medical histories and clinical findings of two schizophrenia twins were almost identical. HRB study demonstrated the presence of 46,XX[55]/47,XXX[4]/48,XXXX[1] constitution in a paranoid schizophrenia case and 46,XX[67]/45,X[5] karyotype in her mother. FISH studies aiming subtelomeric chromosomal regions revealed no rearrangements and 22q11.2 regions were intact in all of the patients. Conclusions. The parental gonadal mosaicism lying at the origin of the mitotic aneuploidy may be the reason for mosaic X chromosome aneuploidies in our mother-daughter schizophrenia couple. Mosaic X chromosome aneuploidies may accompany schizophrenia cases and may contribute to pathogenesis of familial schizophrenia.

Neuregulin-1, the fetal endothelium, and brain damage in preterm newborns

OBJECTIVE

To assess the potential role for Neuregulin-1 (NRG1) as a systemic endogenous protector in the setting of perinatal inflammatory brain damage.

METHODS

We measured NRG1-protein and mRNA levels in human umbilical venous endothelial cells (HUVECs) of different gestational ages at various durations of exposure to lipopolysaccharide (LPS). In parallel, we genotyped the donor individuals for SNP8NRG221533, a disease-related single nucleotide polymorphism in the 5' region upstream of the NRG1 sequence. Intracellular NRG1 localization was visualized by confocal microscopy. Furthermore we analyzed the relationship between SNP8NRG221533 genotype and neurodevelopmental outcome in children born preterm.

RESULTS

We observed a positive dose-response-relationship between NRG1-mRNA and intracellular protein levels with both advancing gestational age and duration of LPS exposure in HUVECs. The presence of allele C at the SNP8NRG221533 locus was associated with an increased cellular production of NRG1 in HUVECs, and with a significantly reduced risk for cerebral palsy and developmental delay in children born preterm.

INTERPRETATION

In conclusion, our data indicate that gestational age, duration of LPS exposure, and the SNP8NRG221533 genotype affect NRG1 levels. Our results support the hypothesis that NRG1 may qualify as an endogenous protector during fetal development.

The dopamine D4 receptor: biochemical and signalling properties

Dopamine is an important neurotransmitter that regulates several key functions in the brain, such as motor output, motivation and reward, learning and memory, and endocrine regulation. Dopamine does not mediate fast synaptic transmission, but rather modulates it by triggering slow-acting effects through the activation of dopamine receptors, which belong to the G-protein-coupled receptor superfamily. Besides activating different effectors through G-protein coupling, dopamine receptors also signal through interaction with a variety of proteins, collectively termed dopamine receptor-interacting proteins. We focus on the dopamine D4 receptor, which contains an important polymorphism in its third intracellular loop. This polymorphism has been the subject of numerous studies investigating links with several brain disorders, such as attention-deficit hyperactivity disorder and schizophrenia. We provide an overview of the structure, signalling properties and regulation of dopamine D4 receptors, and briefly discuss their physiological and pathophysiological role in the brain.

Can the role of genetic factors in schizophrenia be enlightened by studies of candidate gene mutant mice behaviour?

Schizophrenia is one of the most severe psychiatric disorders. Despite the knowledge accumulated over years, aetiology and pathophysiology remain uncertain. Research on families and twins suggests that genetic factors are largely responsible for the disease and implies specific genes as risk factors. Genetic epidemiology indicates a complex transmission mode, compatible with a multi-locus model, with single genes accounting for specific traits rather than for the entire phenotype. To better understand every single gene contribution to schizophrenia, the use of intermediate endophenotypes has been proposed. A straight communication between preclinical and clinical researchers could facilitate research on the association between genes and endophenotypes. Many behavioural tasks are available for humans and animals to measure endophenotypes. Here, firstly, we reviewed the most promising mouse behavioural tests modelling human behavioural tasks altered in schizophrenia. Secondly, we systematically reviewed animal models availability for a selection of candidate genes, derived from linkage and association studies. Thirdly, we systematically reviewed the studies which tested mutant mice in the above behavioural tasks. Results indicate a large mutant mice availability for schizophrenia candidate genes but they have been insufficiently tested in behavioural tasks. On the other hand, multivariate and translational approach should be implemented in several behavioural domains.

DTNBP1 is associated with imaging phenotypes in schizophrenia

Dystrobrevin binding protein 1 (DTNBP1) has been identified as putative schizophrenia susceptibility gene, but it remains unknown whether polymorphisms relate to altered cerebral structure. We examined relationships between a previously implicated DTNBP1 risk variant [P1578] and global and segmented brain tissue volumes and regional cortical thickness in schizophrenia (n = 62; 24 risk carriers) and healthy subjects (n = 42; 11 risk carriers), across ethnic groups and within Caucasians. Schizophrenia patients showed similar brain volumes, but significantly reduced brain-size adjusted gray matter and CSF volumes and cortical thinning in a widespread neocortical distribution compared to controls. DTNBP1 risk was found associated with reduced brain volume, but not with tissue sub-compartments. Cortical thickness, which was weakly associated with brain size, showed regional variations in association with genetic risk, although effects were dominated by highly significant genotype by diagnosis interactions over broad areas of cortex. Risk status was found associated with regional cortical thinning in patients, particularly in temporal networks, but with thickness increases in controls. DTNBP1 effects for brain volume and cortical thickness appear driven by different neurobiological processes. Smaller brain volumes observed in risk carriers may relate to previously reported DTNBP1/cognitive function relationships irrespective of diagnosis. Regional cortical thinning in patient, but not in control risk carriers, may suggest that DTNBP1 interacts with other schizophrenia-related risk factors to affect laminar thickness. Alternatively, DTNBP1 may influence neural processes for which individuals with thicker cortex are less vulnerable. Although DTNBP1 relates to cortical thinning in schizophrenia, morphological changes in the disorder are influenced by additional genetic and/or environmental factors.

Animal models of schizophrenia

Schizophrenia may well represent one of the most heterogenous mental disorders in human history. This heterogeneity encompasses (1) etiology; where numerous putative genetic and environmental factors may contribute to disease manifestation, (2) symptomatology; with symptoms characterized by group; positive--behaviors not normally present in healthy subjects (e.g. hallucinations), negative--reduced expression of normal behaviors (e.g. reduced joy), and cognitive--reduced cognitive capabilities separable from negative symptoms (e.g. impaired attention), and (3) individual response variation to treatment. The complexity of this uniquely human disorder has complicated the development of suitable animal models with which to assay putative therapeutics. Moreover, the development of animal models is further limited by a lack of positive controls because currently approved therapeutics only addresses psychotic symptoms, with minor negative symptom treatment. Despite these complexities however, many animal models of schizophrenia have been developed mainly focusing on modeling individual symptoms. Validation criteria have been established to assay the utility of these models, determining the (1) face, (2) predictive, (3) construct, and (4) etiological validities, as well as (5) reproducibility of each model. Many of these models have been created following the development of major hypotheses of schizophrenia, including the dopaminergic, glutamatergic, and neurodevelopmental hypotheses. The former two models have largely consisted of manipulating these neurotransmitter systems to produce behavioral abnormalities with some relevance to symptoms or putative etiology of schizophrenia. Given the serotonergic link to hallucinations and cholinergic link to attention, other models have manipulated these systems also. Finally, there has also been a drive toward creating mouse models of schizophrenia utilizing transgenic technology. Thus, there are opportunities to combine both environmental and genetic factors to create more suitable models of schizophrenia. More sophisticated animal tasks are also being created with which to ascertain whether these models produce behavioral abnormalities consistent with patients with schizophrenia. While animal models of schizophrenia continue to be developed, we must be cognizant that (1) validating these models are limited to the degree by which Clinicians can provide relevant information on the behavior of these patients, and (2) any putative treatments that are developed are also likely to be given with concurrent antipsychotic treatment. While our knowledge of this devastating disorder increases and our animal models and tasks with which to measure their behaviors become more sophisticated, caution must still be taken when validating these models to limit complications when introducing putative therapeutics to human trials.

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.

Association of tagging single nucleotide polymorphisms on 8 candidate genes in dopaminergic pathway with schizophrenia in Croatian population

AIM

To perform a comprehensive evaluation of association of common genetic variants in candidate genes in the dopaminergic pathway with schizophrenia in a sample from Croatian population.

METHODS

A case-control association study was performed on 104 unrelated patients with schizophrenia recruited from a psychiatric hospital in Zagreb and 131 phenotypically normal Croatian subjects. Forty-nine tagging single nucleotide polymorphisms (tagSNPs) in 8 candidate genes in the dopaminergic pathway were identified from the HapMap database and tested for association. Genotyping was performed using the SNPlex platform. Statistical analysis was conducted to assess allelic and genotypic associations between cases and controls using a goodness of fit chi(2) test and trend test, respectively; adjustment for multiple testing was done by permutation based analysis.

RESULTS

Significant allele frequency differences between schizophrenia cases and controls were observed at 4 tagSNPs located in the genes DRD5, HTR1B1, DBH, and TH1 (P<0.005). A trend test also confirmed the genotypic association (P<0.001) of these 4 tagSNPs. Additionally, moderate association (P<0.05) was observed with 8 tagSNPs on SLC6A3, DBH, DRD4, SLC6A4, and COMT.

CONCLUSIONS

Common genetic variants in genes involved in the dopaminergic pathway are associated with schizophrenia in the populations of Caucasian descent.

Neighborhood differences in psychoses: prevalence of psychotic disorders in two socially-differentiated metropolitan areas of Barcelona

INTRODUCTION

The prevalence of schizophrenia and other psychoses can vary between close geographic locations and can be biased by the use of epidemiological designs. With data derived from a public mental health centre with close relations to primary care teams we have compared the distribution of psychotic disorders in two neighborhoods in Barcelona with marked psycho-social differences.

METHODS

Using a computerized database from Barcelona's National Health Service covering 5 basic health-care areas with a total population of 103,615 inhabitants, we have accessed case records showing any psycho-pathology between the years of 1982 and 2000.

RESULTS

From the case records of 21,536 registered patients showing any psycho-pathology, and using strict diagnostic, clinical and assistance criteria, we found that there were 476 patients diagnosed as "schizophrenic" and 362 that were "affected by other psychoses." Despite being evaluated by the same mental health personal, the same research team using identical criteria and over the same period of time (thus precluding operator and selection bias) the prevalence of these disorders was twice as high in La Mina (a district with a marked accumulation of psycho-social risk-factors) as compared to the neighboring district of La Verneda.

CONCLUSIONS

When assessing prevalence of psychoses, it is necessary to consider the impact of social and psycho-social factors, even in neighboring communities.

Association between the DRD2-141C Insertion/Deletion polymorphism and schizophrenia

Epidemiological studies have demonstrated that the genetic component is an important risk factor for the development of schizophrenia. The genes that codify the different compounds of the dopaminergic system have created interest for molecular investigations in patients with schizophrenia because the antipsychotic drugs, especially those of first generation, act on this cerebral system. Thus the aim of the present study was to investigate the possible association between the -141 Ins/Del (rs1799732) polymorphism of the dopamine receptor type 2 (DRD2) and schizophrenia. The distribution of the alleles and genotypes of the studied polymorphism was investigated in a sample of 229 patients and 733 controls. There were statistical differences in the allelic (χ2=9.78; p=0.001) and genotypic genotypic (χ2=12.74; p=0.001) distributions between patients and controls. Thus the -141C Ins/Del polymorphism of the DRD2 gene (allele Ins) was associated to the SCZ phenotype in the investigated sample.

Gene expression in the prefrontal cortex during adolescence: implications for the onset of schizophrenia

Background

Many critical maturational processes take place in the human brain during postnatal development. In particular, the prefrontal cortex does not reach maturation until late adolescence and this stage is associated with substantial white matter volume increases. Patients with schizophrenia and other major psychiatric disorders tend to first present with overt symptoms during late adolescence/early adulthood and it has been proposed that this developmental stage represents a "window of vulnerability".

Methods

In this study we used whole genome microarrays to measure gene expression in post mortem prefrontal cortex tissue from human individuals ranging in age from 0 to 49 years. To identify genes specifically altered in the late adolescent period, we applied a template matching procedure. Genes were identified which showed a significant correlation to a template showing a peak of expression between ages 15 and 25.

Results

Approximately 2000 genes displayed an expression pattern that was significantly correlated (positively or negatively) with the template. In the majority of cases, these genes in fact reached a plateau during adolescence with only subtle changes thereafter. These include a number of genes previously associated with schizophrenia including the susceptibility gene neuregulin 1 (NRG1). Functional profiling revealed peak expression in late adolescence for genes associated with energy metabolism and protein and lipid synthesis, together with decreases for genes involved in glutamate and neuropeptide signalling and neuronal development/plasticity. Strikingly, eight myelin-related genes previously found decreased in schizophrenia brain tissue showed a peak in their expression levels in late adolescence, while the single myelin gene reported increased in patients with schizophrenia was decreased in late adolescence.

Conclusion

The observed changes imply that molecular mechanisms critical for adolescent brain development are disturbed in schizophrenia patients.

Genomewide association studies: history, rationale, and prospects for psychiatric disorders

OBJECTIVE

The authors conducted a review of the history and empirical basis of genomewide association studies (GWAS), the rationale for GWAS of psychiatric disorders, results to date, limitations, and plans for GWAS meta-analyses.

METHOD

A literature review was carried out, power and other issues discussed, and planned studies assessed.

RESULTS

Most of the genomic DNA sequence differences between any two people are common (frequency >5%) single nucleotide polymorphisms (SNPs). Because of localized patterns of correlation (linkage disequilibrium), 500,000 to 1,000,000 of these SNPs can test the hypothesis that one or more common variants explain part of the genetic risk for a disease. GWAS technologies can also detect some of the copy number variants (deletions and duplications) in the genome. Systematic study of rare variants will require large-scale resequencing analyses. GWAS methods have detected a remarkable number of robust genetic associations for dozens of common diseases and traits, leading to new pathophysiological hypotheses, although only small proportions of genetic variance have been explained thus far and therapeutic applications will require substantial further effort. Study design issues, power, and limitations are discussed. For psychiatric disorders, there are initial significant findings for common SNPs and for rare copy number variants, and many other studies are in progress.

CONCLUSIONS

GWAS of large samples have detected associations of common SNPs and of rare copy number variants with psychiatric disorders. More findings are likely, since larger GWAS samples detect larger numbers of common susceptibility variants, with smaller effects. The Psychiatric GWAS Consortium is conducting GWAS meta-analyses for schizophrenia, bipolar disorder, major depressive disorder, autism, and attention deficit hyperactivity disorder. Based on results for other diseases, larger samples will be required. The contribution of GWAS will depend on the true genetic architecture of each disorder.

TRIM32 is an E3 ubiquitin ligase for dysbindin

Mutations in the gene encoding tripartite motif protein 32 (TRIM32) cause two seemingly diverse diseases: limb-girdle muscular dystrophy type 2H (LGMD2H) or sarcotubular myopathy (STM) and Bardet–Biedl syndrome type 11(BBS11). Although TRIM32 is involved in protein ubiquitination, its substrates and the molecular consequences of disease-causing mutations are poorly understood. In this paper, we show that TRIM32 is a widely expressed ubiquitin ligase that is localized to the Z-line in skeletal muscle. Using the yeast two-hybrid system, we found that TRIM32 binds and ubiquitinates dysbindin, a protein implicated in the genetic aetiology of schizophrenia, augmenting its degradation. Small-interfering RNA-mediated knock-down of TRIM32 in myoblasts resulted in elevated levels of dysbindin. Importantly, the LGMD2H/STM-associated TRIM32 mutations, D487N and R394H impair ubiquitin ligase activity towards dysbindin and were mislocalized in heterologous cells. These mutants were able to self-associate and also co-immunoprecipitated with wild-type TRIM32 in transfected cells. Furthermore, the D487N mutant could bind to both dysbindin and its E2 enzyme but was defective in monoubiquitination. In contrast, the BBS11 mutant P130S did not show any biochemical differences compared with the wild-type protein. Our data identify TRIM32 as a regulator of dysbindin and demonstrate that the LGMD2H/STM mutations may impair substrate ubiquitination.

Linkage analysis of schizophrenia in African-American families

While many studies have sought a window into the genetics of schizophrenia, few have focused on African-American families. An exception is the Project among African-Americans to Explore Risks for Schizophrenia (PAARTNERS), which seeks to identify novel and known risk variation for schizophrenia by genetic analyses of African-American families. We report a linkage study of diagnostic status in 217 African-American families using the Illumina Linkage Panel. Due to assumed incomplete and time-dependent penetrance, we performed linkage analysis using two different treatments of diagnosis: (1) treating both affected and unaffected individuals as informative for linkage (using the program SIBPAL) and (2) treating only affected individuals as informative (using the program MERLIN). We also explore three definitions of affected status: narrowly defined schizophrenia; one broadened to include schizoaffective disorder; and another including all diagnoses indicating psychosis. Several regions show a decrease in the evidence for linkage as the definition broadens 8q22.1 (rs911, 99.26 cM; SIBPAL p-value [p] goes from 0.006 to 0.02), 16q24.3 (rs1006547, 130.48 cM; p from 0.00095 to 0.0085), and 20q13.2 (rs1022689, 81.73 cM; p from 0.00015 to 0.032). One region shows a substantial increase in evidence for linkage, 11p15.2 (rs722317, 24.27 cM; p from 0.0022 to 0.0000003); MERLIN results support the significance of the SIBPAL results (p=0.00001). Our linkage results overlap two broad, previously-reported linkage regions: 8p23.3-p12 found in studies sampling largely families of European ancestry; and 11p11.2-q22.3 reported by a study of African-American families. These results should prove quite useful for uncovering loci affecting risk for schizophrenia.

Using the MATRICS to guide development of a preclinical cognitive test battery for research in schizophrenia

Cognitive deficits in schizophrenia are among the core symptoms of the disease, correlate with functional outcome, and are not well treated with current antipsychotic therapies. In order to bring together academic, industrial, and governmental bodies to address this great 'unmet therapeutic need', the NIMH sponsored the Measurement and Treatment Research to Improve Cognition in Schizophrenia (MATRICS) initiative. Through careful factor analysis and consensus of expert opinion, MATRICS identified seven domains of cognition that are deficient in schizophrenia (attention/vigilance, working memory, reasoning and problem solving, processing speed, visual learning and memory, verbal learning and memory, and social cognition) and recommended a specific neuropsychological test battery to probe these domains. In order to move the field forward and outline an approach for translational research, there is a need for a "preclinical MATRICS" to develop a rodent test battery that is appropriate for drug development. In this review, we outline such an approach and review current rodent tasks that target these seven domains of cognition. The rodent tasks are discussed in terms of their validity for probing each cognitive domain as well as a brief overview of the pharmacology and manipulations relevant to schizophrenia for each task.

Fine mapping on chromosome 10q22-q23 implicates Neuregulin 3 in schizophrenia

Linkage studies have implicated 10q22-q23 as a schizophrenia (SZ) susceptibility locus in Ashkenazi Jewish (AJ) and Han Chinese from Taiwan populations. To further explore our previous linkage signal in the AJ population (NPL score: 4.27, empirical p = 2 x 10(-5)), we performed a peakwide association fine mapping study by using 1414 SNPs across approximately 12.5 Mb in 10q22-q23. We genotyped 1515 AJ individuals, including 285 parent-child trios, 173 unrelated cases, and 487 unrelated controls. We analyzed the binary diagnostic phenotype of SZ and 9 heritable quantitative traits derived from a principal components factor analysis of 73 items from our consensus diagnostic ratings and direct assessment interviews. Although no marker withstood multiple test correction for association with the binary SZ phenotype, we found strong evidence of association by using the "delusion" factor as the quantitative trait at three SNPs (rs10883866, rs10748842, and rs6584400) located in a 13 kb interval in intron 1 of Neuregulin 3 (NRG3). Our best p value from family-based association analysis was 7.26 x 10(-7). We replicated this association in the collection of 173 unrelated AJ cases (p = 1.55 x 10(-2)), with a combined p value of 2.30 x 10(-7). After performing 10,000 permutations of each of the phenotypes, we estimated the empirical study-wide significance across all 9 factors (90,000 permutations) to be p = 2.7 x 10(-3). NRG3 is primarily expressed in the central nervous system and is one of three paralogs of NRG1, a gene strongly implicated in SZ. These biological properties together with our linkage and association results strongly support NRG3 as a gene involved in SZ.