Schizophrenia and affective disorders--cosegregation with a translocation at chromosome 1q42 that directly disrupts brain-expressed genes: clinical and P300 findings in a family

Wnt and lithium: a common destiny in the therapy of nervous system pathologies?

Wnt signaling is required for neurogenesis, the fate of neural progenitors, the formation of neuronal circuits during development, neuron positioning and polarization, axon and dendrite development and finally for synaptogenesis. This signaling pathway is also implicated in the generation and differentiation of glial cells. In this review, we describe the mechanisms of action of Wnt signaling pathways and their implication in the development and correct functioning of the nervous system. We also illustrate how a dysregulated Wnt pathway could lead to psychiatric, neurodegenerative and demyelinating pathologies. Lithium, used for the treatment of bipolar disease, inhibits GSK3β, a central enzyme of the Wnt/β-catenin pathway. Thus, lithium could, to some extent, mimic Wnt pathway. We highlight the possible dialogue between lithium therapy and modulation of Wnt pathway in the treatment of the diseases of the nervous system.

Resting EEG in psychosis and at-risk populations--a possible endophenotype?

BACKGROUND

Finding reliable endophenotypes for psychosis could lead to an improved understanding of aetiology, and provide useful alternative phenotypes for genetic association studies. Resting quantitative electroencephalography (QEEG) activity has been shown to be heritable and reliable over time. However, QEEG research in patients with psychosis has shown inconsistent and even contradictory findings, and studies of at-risk populations are scarce. Hence, this study aimed to investigate whether resting QEEG activity represents a candidate endophenotype for psychosis.

METHOD

QEEG activity at rest was compared in four frequency bands (delta, theta, alpha, and beta), between chronic patients with psychosis (N=48), first episode patients (N=46), at-risk populations ("at risk mental state", N=33; healthy relatives of patients, N=45), and healthy controls (N=107).

RESULTS

Results showed that chronic patients had significantly increased resting QEEG amplitudes in delta and theta frequencies compared to healthy controls. However, first episode patients and at-risk populations did not differ from controls in these frequency bands. There were no group differences in alpha or beta frequency bands.

CONCLUSION

Since no abnormalities were found in first episode patients, ARMS, or healthy relatives, resting QEEG activity in the frequency bands examined is unlikely to be related to genetic predisposition to psychosis. Rather than endophenotypes, the low frequency abnormalities observed in chronic patients are probably related to illness progression and/or to the long-term effects of treatments.

Transcriptome profiling of human hippocampus dentate gyrus granule cells in mental illness

This study is, to the best of our knowledge, the first application of whole transcriptome sequencing (RNA-seq) to cells isolated from postmortem human brain by laser capture microdissection. We investigated the transcriptome of dentate gyrus (DG) granule cells in postmortem human hippocampus in 79 subjects with mental illness (schizophrenia, bipolar disorder, major depression) and nonpsychiatric controls. We show that the choice of normalization approach for analysis of RNA-seq data had a strong effect on results; under our experimental conditions a nonstandard normalization method gave superior results. We found evidence of disrupted signaling by miR-182 in mental illness. This was confirmed using a novel method of leveraging microRNA genetic variant information to indicate active targeting. In healthy subjects and those with bipolar disorder, carriers of a high- vs those with a low-expressing genotype of miR-182 had different levels of miR-182 target gene expression, indicating an active role of miR-182 in shaping the DG transcriptome for those subject groups. By contrast, comparing the transcriptome between carriers of different genotypes among subjects with major depression and schizophrenia suggested a loss of DG miR-182 signaling in these conditions.

DISC1 complexes with TRAK1 and Miro1 to modulate anterograde axonal mitochondrial trafficking

Disrupted-In-Schizophrenia 1 (DISC1) is a candidate risk factor for schizophrenia, bipolar disorder and severe recurrent depression. Here, we demonstrate that DISC1 associates robustly with trafficking-protein-Kinesin-binding-1 which is, in turn, known to interact with the outer mitochondrial membrane proteins Miro1/2, linking mitochondria to the kinesin motor for microtubule-based subcellular trafficking. DISC1 also associates with Miro1 and is thus a component of functional mitochondrial transport complexes. Consistent with these observations, in neuronal axons DISC1 promotes specifically anterograde mitochondrial transport. DISC1 thus participates directly in mitochondrial trafficking, which is essential for neural development and neurotransmission. Any factor affecting mitochondrial DISC1 function is hence likely to have deleterious consequences for the brain, potentially contributing to increased risk of psychiatric illness. Intriguingly, therefore, a rare putatively causal human DISC1 sequence variant, 37W, impairs the ability of DISC1 to promote anterograde mitochondrial transport. This is likely related to a number of mitochondrial abnormalities induced by expression of DISC1-37W, which redistributes mitochondrial DISC1 and enhances kinesin mitochondrial association, while also altering protein interactions within the mitochondrial transport complex.

The emerging molecular architecture of schizophrenia, polygenic risk scores and the clinical implications for GxE research

Schizophrenia is a devastating mental disorder. The level of risk in the general population is sustained by the persistence of social, environmental and biological factors, as well as their interactions. Socio-environmental risk factors for schizophrenia are well established and robust. The same can belatedly be said of genetic risk factors for the disorder. Recent progress in schizophrenia genetics is primarily fuelled by genome-wide association, which is able to leverage substantial proportions of additional explained variance previously classified as 'missing'. Here, we provide an outline of the emerging genetic landscape of schizophrenia and demonstrate how this knowledge can be turned into a simple empirical measure of genetic risk, known as a polygenic risk score. We highlight the statistical framework used to assess the clinical potential of the new score and finally, draw relevance to and discuss the clinical implications for the study of gene-environment interaction.

Drug discovery based on genetic and metabolic findings in schizophrenia

Recent progress in the genetics of schizophrenia provides the rationale for re-evaluating causative factors and therapeutic strategies for this disease. Here, we review the major candidate susceptibility genes and relate the aberrant function of these genes to defective regulation of energy metabolism in the schizophrenic brain. Disturbances in energy metabolism potentially lead to neurodevelopmental deficits, impaired function of the mature nervous system and failure to maintain neurites/dendrites and synaptic connections. Current antipsychotic drugs do not specifically address these underlying deficits; therefore, a new generation of more effective medications is urgently needed. Novel targets for future drug discovery are identified in this review. The coordinated application of structure-based drug design, systems biology and research on model organisms may greatly facilitate the search for next-generation antipsychotic drugs.

Revitalizing psychiatric therapeutics

Despite high prevalence and enormous unmet medical need, the pharmaceutical industry has recently de-emphasized neuropsychiatric disorders as 'too difficult' a challenge to warrant major investment. Here I describe major obstacles to drug discovery and development including a lack of new molecular targets, shortcomings of current animal models, and the lack of biomarkers for clinical trials. My major focus, however, is on new technologies and scientific approaches to neuropsychiatric disorders that give promise for revitalizing therapeutics and may thus answer industry's concerns.

Postmortem brain: an underutilized substrate for studying severe mental illness

We propose that postmortem tissue is an underutilized substrate that may be used to translate genetic and/or preclinical studies, particularly for neuropsychiatric illnesses with complex etiologies. Postmortem brain tissues from subjects with schizophrenia have been extensively studied, and thus serve as a useful vehicle for illustrating the challenges associated with this biological substrate. Schizophrenia is likely caused by a combination of genetic risk and environmental factors that combine to create a disease phenotype that is typically not apparent until late adolescence. The complexity of this illness creates challenges for hypothesis testing aimed at understanding the pathophysiology of the illness, as postmortem brain tissues collected from individuals with schizophrenia reflect neuroplastic changes from a lifetime of severe mental illness, as well as treatment with antipsychotic medications. While there are significant challenges with studying postmortem brain, such as the postmortem interval, it confers a translational element that is difficult to recapitulate in animal models. On the other hand, data derived from animal models typically provide specific mechanistic and behavioral measures that cannot be generated using human subjects. Convergence of these two approaches has led to important insights for understanding molecular deficits and their causes in this illness. In this review, we discuss the problem of schizophrenia, review the common challenges related to postmortem studies, discuss the application of biochemical approaches to this substrate, and present examples of postmortem schizophrenia studies that illustrate the role of the postmortem approach for generating important new leads for understanding the pathophysiology of severe mental illness.

Emerging epigenetic mechanisms of long non-coding RNAs

Long non-coding RNAs (lncRNAs) have been increasingly appreciated as an integral component of gene regulatory networks. Genome-wide features of their origin and expression patterns ascribed a prominent role for lncRNAs to the regulation of protein-coding genes, and also suggest a potential link to many human diseases. Recent studies have begun to unravel the intricate regulatory mechanism of lncRNAs occurring at multiple levels. The brain is one of the richest sources of lncRNAs, many of which have already shown a close relationship with genes or genetic loci implicated in a wide range of neurological disorders. This review describes recently emerging mechanistic principles of lncRNA functions to provide neuroscientists with molecular insights that will help future research on lncRNAs in the brain.

Role of neuropeptides in anxiety, stress, and depression: from animals to humans

Major depression, with its strikingly high prevalence, is the most common cause of disability in communities of Western type, according to data of the World Health Organization. Stress-related mood disorders, besides their deleterious effects on the patient itself, also challenge the healthcare systems with their great social and economic impact. Our knowledge on the neurobiology of these conditions is less than sufficient as exemplified by the high proportion of patients who do not respond to currently available medications targeting monoaminergic systems. The search for new therapeutical strategies became therefore a "hot topic" in neuroscience, and there is a large body of evidence suggesting that brain neuropeptides not only participate is stress physiology, but they may also have clinical relevance. Based on data obtained in animal studies, neuropeptides and their receptors might be targeted by new candidate neuropharmacons with the hope that they will become important and effective tools in the management of stress related mood disorders. In this review, we attempt to summarize the latest evidence obtained using animal models for mood disorders, genetically modified rodent models for anxiety and depression, and we will pay some attention to previously published clinical data on corticotropin releasing factor, urocortin 1, urocortin 2, urocortin 3, arginine-vasopressin, neuropeptide Y, pituitary adenylate-cyclase activating polypeptide, neuropeptide S, oxytocin, substance P and galanin fields of stress research.

Role of disrupted in schizophrenia 1 (DISC1) in stress-induced prefrontal cognitive dysfunction

Recent genetic studies have linked mental illness to alterations in disrupted in schizophrenia 1 (DISC1), a multifunctional scaffolding protein that regulates cyclic adenosine monophosphate (cAMP) signaling via interactions with phosphodiesterase 4 (PDE4). High levels of cAMP during stress exposure impair function of the prefrontal cortex (PFC), a region gravely afflicted in mental illness. As stress can aggravate mental illness, genetic insults to DISC1 may worsen symptoms by increasing cAMP levels. The current study examined whether viral knockdown (KD) of the Disc1 gene in rat PFC increases susceptibility to stress-induced PFC dysfunction. Rats were trained in a spatial working memory task before receiving infusions of (a) an active viral construct that knocked down Disc1 in PFC (DISC1 KD group), (b) a 'scrambled' construct that had no effect on Disc1 (Scrambled group), or (c) an active construct that reduced DISC1 expression dorsal to PFC (Anatomical Control group). Data were compared with an unoperated Control group. Cognitive performance was assessed following mild restraint stress that had no effect on normal animals. DISC1 KD rats were impaired by 1  h restraint stress, whereas Scrambled, Control, and Anatomical Control groups were unaffected. Thus, knocking down Disc1 in PFC reduced the threshold for stress-induced cognitive dysfunction, possibly through disinhibited cAMP signaling at neuronal network synapses. These findings may explain why patients with DISC1 mutations may be especially vulnerable to the effects of stress.

Family history of psychosis moderates early auditory cortical response abnormalities in non-psychotic bipolar disorder

OBJECTIVES

Bipolar I disorder is a disabling illness affecting 1% of people worldwide. Family and twin studies suggest that psychotic bipolar disorder (BDP) represents a homogeneous subgroup with an etiology distinct from non-psychotic bipolar disorder (BDNP) and partially shared with schizophrenia. Studies of auditory electrophysiology [e.g., paired-stimulus and oddball measured with electroencephalography (EEG)] consistently report deviations in psychotic groups (schizophrenia, BDP), yet such studies comparing BDP and BDNP are sparse and, in some cases, conflicting. Auditory EEG responses are significantly reduced in unaffected relatives of psychosis patients, suggesting that they may relate to both psychosis liability and expression.

METHODS

While 64-sensor EEGs were recorded, age- and gender-matched samples of 70 BDP, 35 BDNP {20 with a family history of psychosis [BDNP(+)]}, and 70 psychiatrically healthy subjects were presented with typical auditory paired-stimuli and auditory oddball paradigms.

RESULTS

Oddball P3b reductions were present and indistinguishable across all patient groups. P2s to paired stimuli were abnormal only in BDP and BDNP(+). Conversely, N1 reductions to stimuli in both paradigms and P3a reductions were present in both BDP and BDNP(-) groups but were absent in BDNP(+).

CONCLUSIONS

Although nearly all auditory neural response components studied were abnormal in BDP, BDNP abnormalities at early- and mid-latencies were moderated by family psychosis history. The relationship between psychosis expression, heritable psychosis risk, and neurophysiology within bipolar disorder, therefore, may be complex. Consideration of such clinical disease heterogeneity may be important for future investigations of the pathophysiology of major psychiatric disturbance.

Disorders and borders: psychiatric genetics and nosology

Over the past century, the definition and classification of psychiatric disorders has evolved through a combination of historical trends, clinical observations, and empirical research. The current nosology, instantiated in the DSM-5 and ICD-10, rests on descriptive criteria agreed upon by a consensus of experts. While the development of explicit criteria has enhanced the reliability of diagnosis, the validity of the current diagnostic categories has been the subject of debate and controversy. Genetic studies have long been regarded as a key resource for validating the boundaries among diagnostic categories. Genetic epidemiologic studies have documented the familiality and heritability of clinically defined psychiatric disorders and molecular genetic studies have begun to identify specific susceptibility variants. At the same time, there is growing evidence from family, twin and genomic studies that genetic influences on psychiatric disorders transcend clinical boundaries. Here I review this evidence for cross-disorder genetic effects and discuss the implications of these findings for psychiatric nosology. Psychiatric genetic research can inform a bottom-up reappraisal of psychopathology that may help the field move beyond a purely descriptive classification and toward an etiology-based nosology.

Association analysis of the DISC1 gene with schizophrenia in the Japanese population and DISC1 immunoreactivity in the postmortem brain

The Disrupted-in-Schizophrenia 1 (DISC1) gene plays a role in the regulation of neural development. Previous evidence from genetic association and biological studies implicates the DISC1 gene as having a role in the pathophysiology of schizophrenia. In the present study, we explored the association between DISC1 missense mutation rs821616 (Ser704Cys) single nucleotide polymorphism (SNP) and four other SNPs (rs1772702, rs1754603, rs821621, rs821624) in the related haplotype block and schizophrenia in the Japanese population. We could not find a significant association of selected SNPs with schizophrenia after correction for multiple testing. We performed a meta-analysis of the Ser704Cys variant in schizophrenia using data from the present study and five previous Japanese population studies, and found no association with schizophrenia. We also examined DISC1 immunoreactivity in postmortem prefrontal cortex specimens of schizophrenia patients compared to control samples. The immunoreactivity revealed a significant decrease of DISC1 protein expression in the schizophrenia samples after ruling out potential confounding factors. However, the Ser704Cys variant did not show effects on DISC1 immunoreactivity. These results provide evidence that this functional genetic variation of DISC1 do not underlie the pathophysiology of schizophrenia in the Japanese population.

DISC1 mouse models as a tool to decipher gene-environment interactions in psychiatric disorders

DISC1 was discovered in a Scottish pedigree in which a chromosomal translocation that breaks this gene segregates with psychiatric disorders, mainly depression and schizophrenia. Linkage and association studies in diverse populations support DISC1 as a susceptibility gene to a variety of neuropsychiatric disorders. Many Disc1 mouse models have been generated to study its neuronal functions. These mouse models display variable phenotypes, some of them relevant to schizophrenia, others to depression. The Disc1 mouse models are popular genetic models for studying gene-environment interactions in schizophrenia. Five different Disc1 models have been combined with environmental factors. The environmental stressors employed can be classified as either early immune activation or later social paradigms. These studies cover major time points along the neurodevelopmental trajectory: prenatal, early postnatal, adolescence, and adulthood. Various combinations of molecular, anatomical and behavioral methods have been used to assess the outcomes. Additionally, three of the studies sought to rescue the resulting abnormalities. Here we provide background on the environmental paradigms used, summarize the results of these studies combining Disc1 mouse models with environmental stressors and discuss what we can learn and how to proceed. A major question is how the genetic and environmental factors determine which psychiatric disorder will be clinically manifested. To address this we can take advantage of the many Disc1 models available and expose them to the same environmental stressor. The complementary experiment would be to expose the same model to different environmental stressors. DISC1 is an ideal gene for this approach, since in the Scottish pedigree the same chromosomal translocation results in different psychiatric conditions.

Cognitive and motivational deficits together with prefrontal oxidative stress in a mouse model for neuropsychiatric illness

Guided by features of molecular, cellular, and circuit dysfunction affecting the prefrontal cortex in clinical investigations, we targeted prefrontal cortex in studies of a model for neuropsychiatric illness using transgenic mice expressing a putative dominant-negative disrupted in schizophrenia 1 (DN-DISC1). We detected marked augmentation of GAPDH-seven in absentia homolog Siah protein binding in the DISC1 mice, a major hallmark of a nuclear GAPDH cascade that is activated in response to oxidative stress. Furthermore, deficits were observed in well-defined tests for the cognitive control of adaptive behavior using reversal learning and reinforcer devaluation paradigms. These deficits occurred even though DN-DISC1 mice showed intact performance in simple associative learning and normal responses in consumption of reward. In an additional series of assessments, motivational functions also were impoverished in DN-DISC1 mice, including tests of the dynamic modulation of reward value by effortful action, progressive ratio performance, and social behavior. Augmentation of an oxidative stress-associated cascade (e.g., a nuclear GAPDH cascade) points to an underlying condition that may contribute to the profile of cognitive and motivational impairments in DN-DISC1 mice by affecting the functional integrity of the prefrontal cortex and dysfunction within its connected networks. As such, this model should be useful for further preclinical research and drug discovery efforts relevant to the burden of prefrontal dysfunction in neuropsychiatric illness.

Prolonged Ketamine Effects in Sp4 Hypomorphic Mice: Mimicking Phenotypes of Schizophrenia

It has been well established that schizophrenia patients display impaired NMDA receptor (NMDAR) functions as well as exacerbation of symptoms in response to NMDAR antagonists. Abnormal NMDAR signaling presumably contributes to cognitive deficits which substantially contribute to functional disability in schizophrenia. Establishing a mouse genetic model will help investigate molecular mechanisms of hypoglutmatergic neurotransmission in schizophrenia. Here, we examined the responses of Sp4 hypomorphic mice to NMDAR antagonists in electroencephalography and various behavioral paradigms. Sp4 hypomorphic mice, previously reported to have reduced NMDAR1 expression and LTP deficit in hippocampal CA1, displayed increased sensitivity and prolonged responses to NMDAR antagonists. Molecular studies demonstrated reduced expression of glutamic acid decarboxylase 67 (GAD67) in both cortex and hippocampus, consistent with abnormal gamma oscillations in Sp4 hypomorphic mice. On the other hand, human SP4 gene was reported to be deleted in schizophrenia. Several human genetic studies suggested the association of SP4 gene with schizophrenia and other psychiatric disorders. Therefore, elucidation of the Sp4 molecular pathway in Sp4 hypomorphic mice may provide novel insights to our understanding of abnormal NMDAR signaling in schizophrenia.

Mouse models of gene-environment interactions in schizophrenia

Gene-environment interactions (GEIs) likely play significant roles in the pathogenesis of schizophrenia and underlie differences in pathological, behavioral, and clinical presentations of the disease. Findings from epidemiology and psychiatric genetics have assisted in the generation of animal models of GEI relevant to schizophrenia. These models may provide a foundation for elucidating the molecular, cellular, and circuitry mechanisms that mediate GEI in schizophrenia. Here we critically review current mouse models of GEI related to schizophrenia, describe directions for their improvement, and propose endophenotypes to provide a more tangible basis for molecular studies of pathways of GEI and facilitate the identification of novel therapeutic targets.

Human brain imaging studies of DISC1 in schizophrenia, bipolar disorder and depression: a systematic review

Disrupted-in-Schizophrenia 1 (DISC1) is a well researched candidate gene for schizophrenia and affective disorders with a range of functions relating to neurodevelopment. Several human brain imaging studies investigating correlations between common and rare variants in DISC1 and brain structure and function have shown conflicting results. A meta-analysis of case/control data showed no association between schizophrenia and any common SNP in DISC1. Therefore it is timely to review the literature to plan the direction of future studies. Twenty-two human brain imaging studies have examined the influence of DISC1 variants in health, schizophrenia, bipolar disorder or depression. The most studied common SNPs are Ser704Cys (rs821616) and Leu607Phe (rs6675281). Some imaging-genomic studies report effects on frontal, temporal and hippocampal structural indices in health and illness and a volumetric longitudinal study supports a putative role for these common SNPs in neurodevelopment. Callosal agenesis is described in association with rare deletions at 1q42 which include DISC1 and rare sequence variants at DISC1 itself. DISC1 interactions with translin-associated factor X (TRAX) and neuregulin have been shown to influence several regional volumes. In the first study involving neonates, a role for Ser704Cys (rs821616) has been highlighted in prenatal brain development with large clusters of reduced grey matter reported in the frontal lobes. Functional MRI studies examining associations between Ser704Cys (rs821616) and Leu607Phe (rs6675281) with prefrontal and hippocampal activation have also given inconsistent results. Prefrontal function was reported to be associated with interaction between DISC1 and CITRON (CIT) in health. Preliminary magnetic resonance spectroscopy and diffusion tensor data support the influence of Ser704Cys (rs821616) status on grey and white matter integrity. The glutamate system remains uninvestigated. Associations between rare sequence variants and structural changes in brain regions including the corpus callosum and effects of gene-gene interactions on brain structure and function are promising areas for future study.

Biomarkers of bipolar disorder: specific or shared with schizophrenia?

Kraepelin's observations of the differences in the course and outcome of dementia praecox and manic depression fundamentally influenced thinking about bipolar disorder (BP) and schizophrenia (SZ) for over a century. In modern times, there is increasing awareness that a greater understanding of the similarities between these two highly prevalent and disabling conditions can teach us as many lessons about the pathophysiology of severe mental disorders as does the pursuit of differentiating factors. We review publications on developmental, genetic, epidemiological, and outcome research that challenges the Kraepelian dichotomy. We highlight the increasing evidence of the overlap in genetic susceptibility. Neuro-developmental studies provide evidence of shared early pathological processes, whilst neurophysiological investigations also suggest that different genes may have a role in the development of both phenotypes. There is also evidence of overlapping neurocognitive phenotypes. It has become increasingly clear that a simple binary classification of these disorders represents an oversimplification. It may be more apposite to think in terms of genetic influences on six continuous symptom dimensions: neurobiological, cognitive, positive, negative, depressive and manic symptoms.

Phenotypic characterization of C57BL/6J mice carrying the Disc1 gene from the 129S6/SvEv strain

Disruption of disrupted-in-schizophrenia 1 (DISC1), a candidate susceptibility gene for schizophrenia, was first identified in a large Scottish family in which many members suffered from various psychiatric disorders, including schizophrenia. To model the Scottish DISC1 truncation, we established a Disc1 mutant mouse line in which the 129S6/SvEv 25-bp deletion variant was transferred into the C57BL/6J strain by backcrossing. A battery of behavioral tasks was conducted to evaluate the basic behaviors and cognitive function of these mice. In heterozygote and homozygote Disc1 mutant (Het and Homo) mice, behavioral impairments were noted in working memory test which is thought to be mediated by the function of the medial prefrontal cortex (mPFC). The properties of mPFC neurons were characterized in both morphological and physiological aspects. The dendritic diameters were decreased in layer II/III mPFC pyramidal neurons of Het and Homo mice, whereas a significant reduction in spine density was observed in Homo mice. Neuronal excitability was declined in layer II/III mPFC pyramidal neurons of Het and Homo mice, yet increased transmitter release was identified in Homo mice. Thus, the structural and functional alterations of the mPFC in Het and Homo mice might account for their cognitive impairment. Since most of the gene knockout mice are generated from 129 substrain-derived embryonic stem cells, potential Disc1 deficiency should be considered.

Personalized medicine in psychiatry: problems and promises

The central theme of personalized medicine is the premise that an individual's unique physiologic characteristics play a significant role in both disease vulnerability and in response to specific therapies. The major goals of personalized medicine are therefore to predict an individual's susceptibility to developing an illness, achieve accurate diagnosis, and optimize the most efficient and favorable response to treatment. The goal of achieving personalized medicine in psychiatry is a laudable one, because its attainment should be associated with a marked reduction in morbidity and mortality. In this review, we summarize an illustrative selection of studies that are laying the foundation towards personalizing medicine in major depressive disorder, bipolar disorder, and schizophrenia. In addition, we present emerging applications that are likely to advance personalized medicine in psychiatry, with an emphasis on novel biomarkers and neuroimaging.

Brain vs behavior: an effect size comparison of neuroimaging and cognitive studies of genetic risk for schizophrenia

Genetic variants associated with increased risk for schizophrenia (SZ) are hypothesized to be more penetrant at the level of brain structure and function than at the level of behavior. However, to date the relative sensitivity of imaging vs cognitive measures of these variants has not been quantified. We considered effect sizes associated with cognitive and imaging studies of 9 robust SZ risk genes (DAOA, DISC1, DTNBP1, NRG1, RGS4, NRGN, CACNA1C, TCF4, and ZNF804A) published between January 2005-November 2011. Summary data was used to calculate estimates of effect size for each significant finding. The mean effect size for each study was categorized as small, medium, or large and the relative frequency of each category was compared between modalities and across genes. Random effects meta-analysis was used to consider the impact of experimental methodology on effect size. Imaging studies reported mostly medium or large effects, whereas cognitive investigations commonly reported small effects. Meta-analysis confirmed that imaging studies were associated with larger effects. Effect size estimates were negatively correlated with sample size but did not differ as a function of gene nor imaging modality. These observations support the notion that SZ risk variants show larger effects, and hence greater penetrance, when characterized using indices of brain structure and function than when indexed by cognitive measures. However, it remains to be established whether this holds true for individual risk variants, imaging modalities, or cognitive functions, and how such effects may be mediated by a relationship with sample size and other aspects of experimental variability.

An emerging role for Wnt and GSK3 signaling pathways in schizophrenia

Schizophrenia is a disabling illness with limited treatment options. The underlying pathophysiology remains unknown, partially due to its heterogeneous nature, and a lack of understanding of the biological functions of genetic risk factors. Several signaling pathways have been implicated, however, with the varying degrees of support. In this article, I will focus on the converging evidence supporting a prominent role for Wnt and glycogen synthase kinase 3 (GSK3) signaling in the biological bases of schizophrenia. This includes current pharmacological therapies that target GSK3, animal model and cell-based studies, and recent human genetic findings that implicate Wnt and GSK3 signaling.

Improving myelin/oligodendrocyte-related dysfunction: a new mechanism of antipsychotics in the treatment of schizophrenia?

Schizophrenia is a severe psychiatric disorder with complex clinical manifestations and its aetiological factors remain unclear. During the past decade, the oligodendrocyte-related myelin dysfunction was proposed as a hypothesis for schizophrenia, supported initially by a series of neuroimaging studies and genetic evidence. Recently, the effects of antipsychotics on myelination and oligodendroglial lineage development and their underlying molecular mechanisms were evaluated. Data from those studies suggest that the antipsychotics-resulting improvement in myelin/oligodendrocyte-related dysfunction may contribute, at least in part, to their therapeutic effect on schizophrenia. Importantly, these findings may provide the basis for a new insight into the therapeutic strategy by targeting the oligodendroglia lineage cells against schizophrenia.

Effects of the adverse life events and Disrupted in Schizophrenia-1 (DISC1) gene polymorphisms on acute symptoms of schizophrenia

The aim of this study was to evaluate the effects of traumatic childhood events and recent adverse life events, as well as the Disrupted in Schizophrenia-1 (DISC1) gene polymorphisms on types of last acute symptoms of patients with schizophrenia. Hundred patients with schizophrenia were given the Childhood Trauma Questionnaire, the Social Readjustment Rating Scale, Scale for Assessment of Positive Symptoms (SAPS), Scale for Assessment of Negative Symptoms (SANS), Brief Psychiatric Rating Scale (BPRS), and Calgary Depression Scale for Schizophrenia (CDSS). The patients' and healthy controls' DISC1 gene was evaluated for the -274G>C, c.791G>A, and c.2110A>T polymorphisms. There was no statistically significant difference with regard to the DISC1 gene polymorphisms between patient and healthy control groups. No significant relationship was found between the -274G>C, c.791G>A, and c.2110A>T haplotypes and development of different acute symptoms of schizophrenia. Having a recent stressful life event significantly affected SAPS (95% confidence interval [CI]=-67.547, -21.473; p=0.00) and BPRS-1 scores (95% CI=-51.405, -6.885; p=0.01), whereas emotional abuse at childhood significantly affected SANS scores (95% CI=-37.300, -10.401; p=0.00). This study shows that features of acute symptoms in schizophrenia are not influenced by the polymorphisms on the DISC1 gene, but are influenced by recent adverse life events and emotional abuse at childhood.

A balanced translocation truncates Neurotrimin in a family with intracranial and thoracic aortic aneurysm

BACKGROUND

Balanced chromosomal rearrangements occasionally have strong phenotypic effects, which may be useful in understanding pathobiology. However, conventional strategies for characterising breakpoints are laborious and inaccurate. We present here a proband with a thoracic aortic aneurysm (TAA) and a balanced translocation t(10;11) (q23.2;q24.2). Our purpose was to sequence the chromosomal breaks in this family to reveal a novel candidate gene for aneurysm.

METHODS AND RESULTS

Intracranial aneurysm (IA) and TAAs appear to run in the family in an autosomal dominant manner: After exploring the family history, we observed that the proband's two siblings both died from cerebral haemorrhage, and the proband's parent and parent's sibling died from aortic rupture. After application of a genome-wide paired-end DNA sequencing method for breakpoint mapping, we demonstrate that this translocation breaks intron 1 of a splicing isoform of Neurotrimin at 11q25 in a previously implicated candidate region for IAs and AAs (OMIM 612161).

CONCLUSIONS

Our results demonstrate the feasibility of genome-wide paired-end sequencing for the characterisation of balanced rearrangements and identification of candidate genes in patients with potentially disease-associated chromosome rearrangements. The family samples were gathered as a part of our recently launched National Registry of Reciprocal Balanced Translocations and Inversions in Finland (n=2575), and we believe that such a registry will be a powerful resource for the localisation of chromosomal aberrations, which can bring insight into the aetiology of related phenotypes.

Cognitive endophenotypes in a family with bipolar disorder with a risk locus on chromosome 4

OBJECTIVES

  We studied cognitive function in high-risk relatives belonging to a single extended family showing linkage of bipolar disorder to a locus on chromosome 4. High-risk relatives were defined as those that carried the risk haplotype of polymorphic markers, identified in a previous linkage study. This family provided a rare opportunity to characterize a neuropsychological endophenotype in a homogeneous sample of relatives with a common genetic risk factor.

METHODS

  Fifteen family members carrying the risk haplotype (eight diagnosed with bipolar disorder or depression and seven with no psychiatric diagnosis), unrelated patients with bipolar disorder (n = 36) and major depressive disorder (n = 40), and healthy control subjects (n = 33) were administered the California Verbal Learning Test, Verbal Fluency Test, Hayling Sentence Completion Test, and Brixton Spatial Anticipation Test to assess verbal memory, verbal fluency, and executive function.

RESULTS

  Compared with healthy controls, family members carrying the risk haplotype were impaired in indices of memory and executive function. There were no significant differences between unaffected and affected haplotype-carrying family members in any cognitive measure. Pronounced deficits in the encoding stage of verbal memory and category verbal fluency were evident in individuals with the risk haplotype.

CONCLUSIONS

  Verbal learning and semantic verbal fluency impairments may represent a cognitive endophenotype for both bipolar disorder and major depression in relatives of bipolar disorder patients, as impairment was also present in high-risk relatives who had not developed any affective disorder symptoms. These findings suggest that impairment in semantic organization may be linked to the genetic aetiology of bipolar disorder.

Deletion at the SLC1A1 glutamate transporter gene co-segregates with schizophrenia and bipolar schizoaffective disorder in a 5-generation family

Growing evidence for genetic overlap between schizophrenia (SCZ) and bipolar disorder (BPD) suggests that causal variants of large effect on disease risk may cross traditional diagnostic boundaries. Extended multigenerational families with both SCZ and BPD cases can be a valuable resource for discovery of shared biological pathways because they can reveal the natural evolution of the underlying genetic disruptions and their phenotypic expression. We investigated a deletion at the SLC1A1 glutamate transporter gene originally identified as a copy number variant exclusively carried by members of a 5-generation Palauan family. Using an expanded sample of 21 family members, quantitative PCR confirmed the deletion in all seven individuals with psychosis, three "obligate-carrier" parents and one unaffected sibling, while four marry-in parents were non-carriers. Linkage analysis under an autosomal dominant model generated a LOD-score of 3.64, confirming co-segregation of the deletion with psychosis. For more precise localization, we determined the approximate deletion end points using alignment of next-generation sequencing data for one affected deletion-carrier and then designed PCR amplicons to span the entire deletion locus. These probes established that the deletion spans 84,298 bp, thus eliminating the entire promoter, the transcription start site, and the first 59 amino acids of the protein, including the first transmembrane Na(2+)/dicarboxylate symporter domain, one of the domains that perform the glutamate transport action. Discovery of this functionally relevant SLC1A1 mutation and its co-segregation with psychosis in an extended multigenerational pedigree provides further support for the important role played by glutamatergic transmission in the pathophysiology of psychotic disorders.

DISC1 (disrupted-in-schizophrenia 1) is associated with cortical grey matter volumes in the human brain: a voxel-based morphometry (VBM) study

DISC1 (Disrupted-In-Schizophrenia 1), one of the top candidate genes for schizophrenia, has been associated with a range of major mental illnesses over the last two decades. DISC1 is crucially involved in neurodevelopmental processes of the human brain. Several haplotypes and single nucleotide polymorphisms of DISC1 have been associated with changes of grey matter volumes in brain regions known to be altered in schizophrenia and other psychiatric disorders. The aim of the present study was to investigate the effects of two single nucleotide polymorphisms (SNPs) of DISC1 on grey matter volumes in human subjects using voxel-based morphometry (VBM). 114/113 participating subjects (psychiatric patients and healthy controls) were genotyped with respect to two at-risk SNPs of DISC1, rs6675281 and rs821616. All participants underwent structural magnetic resonance imaging (MRI). MRI data was statistically analyzed using voxel-based morphometry. We found significant alterations of grey matter volumes in prefrontal and temporal brain regions in association with rs6675281 and rs821616. These effects of DISC1 polymorphisms on brain morphology provide further support for an involvement of DISC1 in the neurobiology of major psychiatric disorders such as schizophrenia.

DISC1 genetics, biology and psychiatric illness

Psychiatric disorders are highly heritable, and in many individuals likely arise from the combined effects of genes and the environment. A substantial body of evidence points towards DISC1 being one of the genes that influence risk of schizophrenia, bipolar disorder and depression, and functional studies of DISC1 consequently have the potential to reveal much about the pathways that lead to major mental illness. Here, we review the evidence that DISC1 influences disease risk through effects upon multiple critical pathways in the developing and adult brain.

DISC1-related signaling pathways in adult neurogenesis of the hippocampus

Disrupted-in-schizophrenia 1 (DISC1) is a multifunctional scaffold protein which plays an important role in neurogenesis and neural development in the adult brain, especially in the dentate gyrus (DG) of the hippocampus. Accumulated research has unveiled the role of DISC1 in several aspects of neural development and neurogenesis, such as neuronal maturation, proliferation, migration, positioning, differentiation, dendritic growth, axonal outgrowth, and synaptic plasticity. Studies on the function of this protein have explored multiple facets, including variants and missense mutants in genetics, proteins interactivity and signaling pathways in molecular biology, and pathogenesis and treatment targets of major mental illness, and more. In this review, we present several signaling pathways discussed in recent research, such as the AKT signaling pathway, GABA signaling pathway, GSK3β signaling pathway, Wnt signaling pathway, and NMDA-R signaling pathway. DISC1 interacts, directly or indirectly, with these signaling pathways and they co-regulate the process of adult neurogenesis in the hippocampus.

Subcortical dopaminergic deficits in a DISC1 mutant model: a study in direct reference to human molecular brain imaging

Imaging of the human brain has been an invaluable aid in understanding neuropsychopharmacology and, in particular, the role of dopamine in the striatum in mental illness. Here, we report a study in a genetic mouse model for major mental illness guided by results from human brain imaging: a systematic study using small animal positron emission tomography (PET), autoradiography, microdialysis and molecular biology in a putative dominant-negative mutant DISC1 transgenic model. This mouse model showed augmented binding of radioligands to the dopamine D2 receptor (D2R) in the striatum as well as neurochemical and behavioral changes to methamphetamine administration. Previously we reported that this model displayed deficits in the forced swim test, a representative indicator of antidepressant efficacy. By combining the results of our two studies, we propose a working hypothesis for future studies that this model might represent a mixed condition of depression and psychosis. We hope that this study will also help bridge a major gap in translational psychiatry between basic characterization of animal models and clinico-pharmacological assessment of patients mainly through PET imaging.

DISC1: a key lead in studying cortical development and associated brain disorders

For the past decade, DISC1 has been studied as a promising lead to understand the biology underlying major mental illnesses, such as schizophrenia. Consequently, many review articles on DISC1 have been published. In this article, rather than repeating comprehensive overviews of research articles, we will introduce the utility of DISC1 in the study of cortical development in association with a wide range of developmental brain disorders. Cortical development involves cell autonomous and cell nonautonomous mechanisms as well as host responses to environmental factors, all of which involve DISC1 function. Thus, we will discuss the significance of DISC1 in forming an overall understanding of multiple mechanisms that orchestrate corticogenesis and can serve as therapeutic targets in diseases caused by abnormal cortical development.

The emerging spectrum of allelic variation in schizophrenia: current evidence and strategies for the identification and functional characterization of common and rare variants

After decades of halting progress, recent large genome-wide association studies (GWAS) are finally shining light on the genetic architecture of schizophrenia. The picture emerging is one of sobering complexity, involving large numbers of risk alleles across the entire allelic spectrum. The aims of this article are to summarize the key genetic findings to date and to compare and contrast methods for identifying additional risk alleles, including GWAS, targeted genotyping and sequencing. A further aim is to consider the challenges and opportunities involved in determining the functional basis of genetic associations, for instance using functional genomics, cellular models, animal models and imaging genetics. We conclude that diverse approaches will be required to identify and functionally characterize the full spectrum of risk variants for schizophrenia. These efforts should adhere to the stringent standards of statistical association developed for GWAS and are likely to entail very large sample sizes. Nonetheless, now more than any previous time, there are reasons for optimism and the ultimate goal of personalized interventions and therapeutics, although still distant, no longer seems unattainable.

Effect of DISC1 on the P300 waveform in psychosis

INTRODUCTION

Abnormalities in the neurophysiological measures P300 amplitude and latency constitute endophenotypes for psychosis. Disrupted-in-Schizophrenia-1 (DISC1) has been proposed as a promising susceptibility gene for schizophrenia, and a previous study has suggested that it is associated with P300 deficits in schizophrenia.

METHODS

We examined the role of variation in DISC1 polymorphisms on the P300 endophenotype in a large sample of patients with schizophrenia or psychotic bipolar disorder (n = 149), their unaffected relatives (n = 130), and unrelated healthy controls (n = 208) using linear regression and haplotype analysis.

RESULTS

Significant associations between P300 amplitude and latency and DISC1 polymorphisms/haplotypes were found. Those homozygous for the A allele of single-nucleotide polymorphism (SNP) rs821597 displayed significantly reduced P300 amplitudes in comparison with homozygous for the G allele (P = .009) and the heterozygous group (P = .018). Haplotype analysis showed a significant association for DISC1 haplotypes (rs3738401|rs6675281|rs821597|rs821616|rs967244|rs980989) and P300 latency. Haplotype GCGTCG and ACGTTT were associated with shorter latencies.

DISCUSSION

The P300 waveform appears to be modulated by variation in individual SNPs and haplotypes of DISC1. Because DISC1 is involved in neurodevelopment, one hypothesis is that disruption in neural connectivity impairs cognitive processes illustrated by P300 deficits observed in this sample.

Evidence for single nucleotide polymorphisms and their association with bipolar disorder

Bipolar disorder (BD) is a complex disorder with a number of susceptibility genes and environmental risk factors involved in its pathogenesis. In recent years, huge progress has been made in molecular techniques for genetic studies, which have enabled identification of numerous genomic regions and genetic variants implicated in BD across populations. Despite the abundance of genetic findings, the results have often been inconsistent and not replicated for many candidate genes/single nucleotide polymorphisms (SNPs). Therefore, the aim of the review presented here is to summarize the most important data reported so far in candidate gene and genome-wide association studies. Taking into account the abundance of association data, this review focuses on the most extensively studied genes and polymorphisms reported so far for BD to present the most promising genomic regions/SNPs involved in BD. The review of association data reveals evidence for several genes (SLC6A4/5-HTT [serotonin transporter gene], BDNF [brain-derived neurotrophic factor], DAOA [D-amino acid oxidase activator], DTNBP1 [dysbindin], NRG1 [neuregulin 1], DISC1 [disrupted in schizophrenia 1]) to be crucial candidates in BD, whereas numerous genome-wide association studies conducted in BD indicate polymorphisms in two genes (CACNA1C [calcium channel, voltage-dependent, L type, alpha 1C subunit], ANK3 [ankyrin 3]) replicated for association with BD in most of these studies. Nevertheless, further studies focusing on interactions between multiple candidate genes/SNPs, as well as systems biology and pathway analyses are necessary to integrate and improve the way we analyze the currently available association data.

Functional role of adult hippocampal neurogenesis as a therapeutic strategy for mental disorders

Adult neurogenesis, the process of generating new neurons from neural stem cells, plays significant roles in synaptic plasticity, memory, and mood regulation. In the mammalian brain, it continues to occur well into adulthood in discrete regions, namely, the hippocampus and olfactory bulb. During the past decade, significant progress has been made in understanding the mechanisms regulating adult hippocampal neurogenesis and its role in the etiology of mental disorders. In addition, adult hippocampal neurogenesis is highly correlated with the remission of the antidepressant effect. In this paper, we discuss three major psychiatric disorders, depression, schizophrenia, and drug addiction, in light of preclinical evidence used in establishing the neurobiological significance of adult neurogenesis. We interpret the significance of these results and pose questions that remain unanswered. Potential treatments which include electroconvulsive therapy, deep brain stimulation, chemical antidepressants, and exercise therapy are discussed. While consensus lacks on specific mechanisms, we highlight evidence which indicates that these treatments may function via an increase in neural progenitor proliferation and changes to the hippocampal circuitry. Establishing a significant role of adult neurogenesis in the pathogenicity of psychiatric disorders may hold the key to potential strategies toward effective treatment.

Wnt signaling: role in Alzheimer disease and schizophrenia

Wnt signaling function starts during the development of the nervous system and is crucial for synaptic plasticity in the adult brain. Clearly Wnt effects in synaptic and plastic processes are relevant, however the implication of this pathway in the prevention of neurodegenerative diseases that produce synaptic impairment, is even more interesting. Several years ago our laboratory found a relationship between the loss of Wnt signaling and the neurotoxicity of the amyloid-β-peptide (Aβ), one of the main players in Alzheimer's disease (AD). Moreover, the activation of the Wnt signaling cascade prevents Aβ-dependent cytotoxic effects. In fact, disrupted Wnt signaling may be a direct link between Aβ-toxicity and tau hyperphosphorylation, ultimately leading to impaired synaptic plasticity and/or neuronal degeneration, indicating that a single pathway can account for both neuro-pathological lesions and altered synaptic function. These observations, suggest that a sustained loss of Wnt signaling function may be a key relevant factor in the pathology of AD. On the other hand, Schizophrenia remains one of the most debilitating and intractable illness in psychiatry. Since Wnt signaling is important in organizing the developing brain, it is reasonable to propose that defects in Wnt signaling could contribute to Schizophrenia, particularly since the neuro-developmental hypothesis of the disease implies subtle dys-regulation of brain development, including some core components of the Wnt signaling pathways such as GSK-3β or Disrupted in Schizophrenia-1 (DISC-1). This review focuses on the relationship between Wnt signaling and its potential relevance for the treatment of neurodegenerative and neuropsychiatric diseases including AD and Schizophrenia.

A role for WNT/β-catenin signaling in the neural mechanisms of behavior

Wnt signaling pathways play a role in a variety of cellular processes including development, cell proliferation, cell fate, and motility. The Wnt/β-catenin pathway is among the most studied of the Wnt pathways and is highly conserved throughout evolution. Recent in vitro and slice physiology experiments have shown that this pathway also functions in synaptic transmission and activity-dependent synaptic plasticity. Since it has now been shown that many components of this signaling pathway are found in the adult brain, Wnt/β-catenin signaling may be important for maintaining and protecting neural connections throughout the lifespan. Here we summarize the role of Wnt/β-catenin signaling in the postnatal brain and discuss recent studies suggesting that deregulated Wnt signaling can result in altered behavior and cognitive disorders.

Losing your inhibition: linking cortical GABAergic interneurons to schizophrenia

GABAergic interneurons of the cerebral cortex (cINs) play crucial roles in many aspects of cortical function. The diverse types of cINs are classified into subgroups according to their morphology, intrinsic physiology, neurochemical markers and synaptic targeting. Recent advances in mouse genetics, imaging and electrophysiology techniques have greatly advanced our efforts to understand the role of normal cIN function and its dysfunction in neuropsychiatric disorders. In schizophrenia (SCZ), a wealth of data suggests that cIN function is perturbed, and that interneuron dysfunction may underlie key symptoms of the disease. In this review, we discuss the link between cINs and SCZ, focusing on the evidence for GABAergic signaling deficits from both SCZ patients and mouse models.