Association between genotype at an exonic SNP in DISC1 and normal cognitive aging

Cataloging the potential SNPs (single nucleotide polymorphisms) associated with quantitative traits, viz. BMI (body mass index), IQ (intelligence quotient) and BP (blood pressure): an updated review

Background

Single nucleotide polymorphism (SNP) variants are abundant, persistent and widely distributed across the genome and are frequently linked to the development of genetic diseases. Identifying SNPs that underpin complex diseases can aid scientists in the discovery of disease-related genes by allowing for early detection, effective medication and eventually disease prevention.

Main body

Various SNP or polymorphism-based studies were used to categorize different SNPs potentially related to three quantitative traits: body mass index (BMI), intelligence quotient (IQ) and blood pressure, and then uncovered common SNPs for these three traits. We employed SNPedia, RefSNP Report, GWAS Catalog, Gene Cards (Data Bases), PubMed and Google Scholar search engines to find relevant material on SNPs associated with three quantitative traits. As a result, we detected three common SNPs for all three quantitative traits in global populations: SNP rs6265 of the BDNF gene on chromosome 11p14.1, SNP rs131070325 of the SL39A8 gene on chromosome 4p24 and SNP rs4680 of the COMT gene on chromosome 22q11.21.

Conclusion

In our review, we focused on the prevalent SNPs and gene expression activities that influence these three quantitative traits. These SNPs have been used to detect and map complex, common illnesses in communities for homogeneity testing and pharmacogenetic studies. High blood pressure, diabetes and heart disease, as well as BMI, schizophrenia and IQ, can all be predicted using common SNPs. Finally, the results of our work can be used to find common SNPs and genes that regulate these three quantitative features across the genome.

Effect of DISC1 Polymorphisms on the Long-term Course of Neurocognitive Deficits in Non-affective Psychosis

Neurocognitive deficits are core symptoms of schizophrenia that determine a poorer outcome. High variability in the progression of neuropsychological deficits in schizophrenia has been described. It is still unknown whether genetic variations can affect the course of cognitive deficits. Variations in the Disrupted in Schizophrenia 1 (DISC1) gene have previously been associated with neurocognitive deficits. This study investigated the association between 3 DISC1 polymorphisms (rs6675281 (Leu607Phe), rs1000731, and rs821616 (Ser704Cys)) and long-term (3 years) cognitive performance. One-hundred-thirty-three Caucasian drug-naive patients experiencing a first episode of non-affective psychosis were genotyped. Cognitive function was assessed at baseline and after 3 years of initiating treatment. Other clinical and socio-demographic variables were recorded to eliminate potential confounding effects. Patients carrying the A allele of rs1000731 exhibited a significant improvement in Working Memory and Attention domains, and the homozygosity of the A allele of rs821616 showed a significant improvement in Motor Dexterity performance over 3 years of follow-up. In conclusion, DISC1 gene variations may affect the course of cognitive deficits found in patients suffering from the first episode of non-affective psychosis.

Genetic Effects of DISC1 and G72 (DAOA) on Visual Learning of Patients with Schizophrenia

BACKGROUND

Visual learning plays an important role in general populations and patients with schizophrenia. Genetic influences on visual learning remain unknown. Two functional single nucleotide polymorphisms (SNPs), Ser704Cys of the DISC1 gene and M24 (rs1421292) of the G72 gene, are strongly associated with pathogenesis and pathophysiology of schizophrenia. This study examined these two SNPs' effects on visual learning in schizophrenia patients.

METHODS

Two hundred seventy-one patients (mean age, 37.0 years [SD = 9.3]; 159 men) with chronic schizophrenia were genotyped for the DISC1 Ser704Cys and G72 M24 SNPs and assessed for visual learning with Visual Reproduction II (delayed reproduction) of Wechsler Memory Scale - III (WMS-III). For comparison, verbal learning (using Word list II of WMS-III) and attention (by Continuous Performance Test) were also measured.

RESULTS

The DISC1 Ser carriers excelled DISC1 Cys/Cys homozygotes in visual learning (p=0.004, effect size: 0.43), but not in other cognitive functions. G72 M24 A-allele carriers and G72 M24 T/T homozygotes performed similarly (effect size: 0.07). In SNP-SNP interaction analysis, the patients with Ser carrier_T/T had better visual learning than those with Cys/Cys_T/T (p=0.004, effect size: 0.70) and those with Cys/Cys_A-allele carrier (p=0.003, effect size: 0.65). Education had a positive effect (p=0.007), while negative symptoms had a negative effect (p<0.001) on visual learning.

CONCLUSION

The findings suggest that genetic variations in DISC1 Ser704Cys and G72 M24 affect visual learning in schizophrenia patients. The effect sizes of SNP-SNP interaction surpassed the sum (0.50) of effect sizes from two individual genes, suggesting synergistic DISC1-G72 interaction.

Additive sex-specific influence of common non-synonymous DISC1 variants on amygdala, basal ganglia, and white cortical surface area in healthy young adults

The disrupted-in-schizophrenia-1 (DISC1) gene is known for its role in the development of mental disorders. It is also involved in neurodevelopment, cognition, and memory. To investigate the association between DISC1 variants and brain morphology, we analyzed the influence of the three common non-synonymous polymorphisms in DISC1 on specific brain structures in healthy young adults. The volumes of brain regions were determined in 145 subjects by magnetic resonance imaging and automated analysis using FreeSurfer. Genotyping was performed by high resolution melting of amplified products. In an additive genetic model, rs6675281 (Leu607Phe), rs3738401 (Arg264Gln), and rs821616 (Ser704Cys) significantly explained the volume variance of the amygdala (p = 0.007) and the pallidum (p = 0.004). A higher cumulative portion of minor alleles was associated with larger volumes of the amygdala (p = 0.005), the pallidum (p = 0.001), the caudate (p = 0.024), and the putamen (p = 0.007). Sex-stratified analysis revealed a strong genetic effect of rs6675281 on putamen and pallidum in females but not in males and an opposite influence of rs3738401 on the white cortical surface in females compared to males. The strongest single association was found for rs821616 and the amygdala volume in male subjects (p < 0.001). No effect was detected for the nucleus accumbens. We report-to our knowledge-for the first time a significant and sex-specific influence of common DISC1 variants on volumes of the basal ganglia, the amygdala and on the cortical surface area. Our results demonstrate that the additive model of all three polymorphisms outperforms their single analysis.

A single exercise bout enhances the manufacture of viral-specific T-cells from healthy donors: implications for allogeneic adoptive transfer immunotherapy

Cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections remain a major cause of morbidity and mortality after allogeneic hematopoietic stem cell transplantation (HSCT). The adoptive transfer of donor-derived viral-specific cytotoxic T-cells (VSTs) is an effective treatment for controlling CMV and EBV infections after HSCT; however, new practical methods are required to augment the ex vivo manufacture of multi-VSTs from healthy donors. This study investigated the effects of a single exercise bout on the ex vivo manufacture of multi-VSTs. PBMCs isolated from healthy CMV/EBV seropositive participants before (PRE) and immediately after (POST) 30-minutes of cycling exercise were stimulated with CMV (pp65 and IE1) and EBV (LMP2A and BMLF1) peptides and expanded over 8 days. The number (fold difference from PRE) of T-cells specific for CMV pp65 (2.6), EBV LMP2A (2.5), and EBV BMLF1 (4.4) was greater among the VSTs expanded POST. VSTs expanded PRE and POST had similar phenotype characteristics and were equally capable of MHC-restricted killing of autologous target cells. We conclude that a single exercise bout enhances the manufacture of multi-VSTs from healthy donors without altering their phenotype or function and may serve as a simple and economical adjuvant to boost the production of multi-VSTs for allogeneic adoptive transfer immunotherapy.

Copy Number Variations in DISC1 and DISC1-Interacting Partners in Major Mental Illness

Robust statistical, genetic and functional evidence supports a role for DISC1 in the aetiology of major mental illness. Furthermore, many of its protein-binding partners show evidence for involvement in the pathophysiology of a range of neurodevelopmental and psychiatric disorders. Copy number variants (CNVs) are suspected to play an important causal role in these disorders. In this study, CNV analysis of DISC1 and its binding partners PAFAH1B1, NDE1, NDEL1, FEZ1, MAP1A, CIT and PDE4B in Scottish and Northern Swedish population-based samples was carried out using multiplex amplicon quantification. Here, we report the finding of rare CNVs in DISC1, NDE1 (together with adjacent genes within the 16p13.11 duplication), NDEL1 (including the overlapping MYH10 gene) and CIT. Our findings provide further evidence for involvement of DISC1 and its interaction partners in neuropsychiatric disorders and also for a role of structural variants in the aetiology of these devastating diseases.

DISC1 regulates trafficking and processing of APP and Aβ generation

We report the novel regulation of proteolytic processing of amyloid precursor protein (APP) by DISC1, a major risk factor for psychiatric illnesses, such as depression and schizophrenia. RNAi knockdown of DISC1 in mature primary cortical neurons led to a significant increase in the levels of intracellular α-C-terminal fragment of APP (APP-CTFα) and the corresponding N-terminal-secreted ectodomain product sAPPα. DISC1 knockdown also elicited a significant decrease in the levels of amyloid beta (Aβ)42 and Aβ40. These aberrant proteolytic events were successfully rescued by co-expression of wild-type DISC1, but not by mutant DISC1 lacking the amino acids required for the interaction with APP, suggesting that APP-DISC1 protein interactions are crucial for the regulation of the C-terminal proteolysis. In a genetically engineered model in which a major full-length DISC1 isoform is depleted, consistent changes in APP processing were seen: an increase in APP-CTFα and decrease in Aβ42 and Aβ40 levels. Finally, we found that knockdown of DISC1 increased the expression of APP at the cell surface and decreased its internalization. The presented DISC1 mechanism of APP proteolytic processing and Aβ peptide generation, which is central to Alzheimer's disease pathology, suggests a novel interface between neurological and psychiatric conditions.

The Disrupted-in-Schizophrenia-1 Ser704Cys polymorphism and brain neurodevelopmental markers in schizophrenia and healthy subjects

Increasing evidence has implicated the role of Disrupted-in-Schizophrenia-1 (DISC1), a potential susceptibility gene for schizophrenia, in early neurodevelopmental processes. However, the effect of its genotype variation on brain morphologic changes related to neurodevelopmental abnormalities in schizophrenia remains largely unknown. This magnetic resonance imaging study examined the association between DISC1 Ser704Cys polymorphism and a range of brain neurodevelopmental markers [cavum septi pellucidi (CSP), adhesio interthalamica (AI), olfactory sulcus depth, and sulcogyral pattern (Types I, II, III, and IV) in the orbitofrontal cortex (OFC)] in an all Japanese sample of 75 schizophrenia patients and 87 healthy controls. The Cys carriers had significantly larger CSP than the Ser homozygotes for both schizophrenia patients and healthy controls. The Cys carriers also exhibited a reduction in the Type I pattern of the right OFC in the healthy controls, but not in the schizophrenia patients. The DISC1 Ser704Cys polymorphism did not affect the AI and olfactory sulcus depth in either group. These results suggested a possible role of the DISC1 genotype in the early neurodevelopment of human brains, but failed to show its specific role in the neurodevelopmental pathology of schizophrenia.

Peripheral DISC1 protein levels as a trait marker for schizophrenia and modulating effects of nicotine

The Disrupted-in-Schizophrenia 1 (DISC1) protein plays a key role in behavioral control and vulnerability for mental illnesses, including schizophrenia. In this study we asked whether peripheral DISC1 protein levels in lymphocytes of patients diagnosed with schizophrenia can serve as a trait marker for the disease. Since a prominent comorbidity of schizophrenia patients is nicotine abuse or addiction, we also examined modulation of lymphocyte DISC1 protein levels in smokers, as well as the relationship between nicotine and DISC1 solubility status. We show decreased DISC1 levels in patients diagnosed with schizophrenia independent of smoking, indicating its potential use as a trait marker of this disease. In addition, lymphocytic DISC1 protein levels were decreased in smoking, mentally healthy individuals but not to the degree of overriding the trait level. Since DISC1 protein has been reported to exist in different solubility states in the brain, we also investigated DISC1 protein solubility in brains of rats treated with nicotine. Sub-chronic treatment with progressively increasing doses of nicotine from 0.25mg/kg to 1mg/kg for 15 days led to a decrease of insoluble DISC1 in the medial prefrontal cortex. Our results demonstrate that DISC1 protein levels in human lymphocytes are correlated with the diagnosis of schizophrenia independent of smoking and thus present a potential biomarker. Reduced DISC1 protein levels in lymphocytes of healthy individuals exposed to nicotine suggest that peripheral DISC1 could have potential for monitoring the effects of psychoactive substances.

A Disrupted-in-Schizophrenia 1 Gene Variant is Associated with Clinical Symptomatology in Patients with First-Episode Psychosis

OBJECTIVE

DISC1 gene is one of the main candidate genes for schizophrenia since it has been associated to the illness in several populations. Moreover, variations in several DISC1 polymorphisms, and in particular Ser704Cys SNP, have been associated in schizophrenic patients to structural and functional modifications in two brain areas (pre-frontal cortex and hippocampus) that play a central role in the genesis of psychotic symptoms. This study tested the association between Ser704Cys DISC1 polymorphism and the clinical onset of psychosis.

METHODS

Two hundred and thirteen Caucasian drug-naive patients experiencing a first episode of non-affective psychosis were genotyped for rs821616 (Ser704Cys) SNP of the DISC1 gene. The clinical severity of the illness was assessed using SAPS and SANS scales. Other clinical and socio-demographic variables were recorded to rule out possible confounding effects.

RESULTS

Patients homozygous for the Ser allele of the Ser704Cys DISC1 SNP had significantly (p<0.05) higher rates at the positive symptoms dimension (SAPS-SANS scales) and hallucinations item, compared to Cys carriers.

CONCLUSION

DISC1 gene variations may modulate the clinical severity of the psychosis at the onset of the disorder.

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.

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.

Involvement of PTPN5, the gene encoding the striatal-enriched protein tyrosine phosphatase, in schizophrenia and cognition

OBJECTIVE

Striatal-enriched protein tyrosine phosphatase (STEP) is a brain-specific member of the protein tyrosine phosphatase (PTP) family that has been implicated in learning and memory. In this study, we examined the association of the protein tyrosine phosphatase non-receptor 5 (PTPN5) gene, which encodes for STEP, with both schizophrenia and cognitive functioning in the Israeli Jewish population.

METHODS

A schizophrenia (SZ) case-control study of 868 participants was carried out (286 patients and 582 controls). Eleven PTPN5 tagging single-nucleotide polymorphisms (SNPs) were selected and single markers and haplotype association analyses were carried out. A cognitive variability study included 437 healthy women who completed a computerized cognitive battery. We performed univariate associations between the SNPs and cognitive performance. The possible functional role of these variants was examined by studying their association with gene expression levels in the brain.

RESULTS

In the SZ study, we found a nominal association in the whole sample between rs4075664 and SZ. Male patients with SZ showed a more significant association for three SNPs (rs4075664, rs2278732, and rs4757710). Haplotypes of the studied SNPs were associated with SZ both in the overall sample and within the male subsample. Expression analysis provided some support for the effects of the associated SNPs on PTPN5 expression level. The cognitive variability study showed positive associations between PTPN5 SNPs and different cognitive subtests. Principal component analysis showed an 'attention index' neurocognitive component that was associated with two SNP pairs (rs10832983 × rs10766504 and rs7932938 × rs4757718).

CONCLUSION

The results imply a model in which PTPN5 may play a role in normal cognitive functioning and contribute to aspects of the neuropathology of SZ.

DISC1 as a therapeutic target for mental illnesses

INTRODUCTION

Many genetic studies have indicated that DISC1 is not merely "disrupted-in-schizophrenia," but is more generally implicated in various brain dysfunctions associated with aberrant neurodevelopment and intracellular signaling pathways. Thus, the DISC1 gene is mildly associated with a variety of brain disorders, including schizophrenia, mood disorders, and autism. This novel concept fits with the results from biological studies of DISC1, which include cell and animal models.

AREAS COVERED

We review the molecular structure and functions of DISC1, particularly those in conjunction with its important interactors. Functions of these interacting proteins are also introduced under the concept of the "DISC1 interactome." Finally, we discuss how the DISC1 interactome can provide potential therapeutic targets for mental illnesses.

EXPERT OPINION

Modulation of DISC1 stability and post-transcriptional modifications may be key targets to address DISC1-related pathology. In addition, modulation of DISC1 interactors and the mechanisms of their interactions with DISC1 may also provide drug targets. Disc1 rodent models can subsequently be used as templates for in vivo validations of compounds designed for DISC1 and its interacting proteins. Furthermore, these rodents will serve as genetic models for schizophrenia and related conditions, especially in conjunction with their pathologies during the neurodevelopmental trajectory.

Molecular genetics of the psychosis phenotype

OBJECTIVE

Relative to recent successes in elucidating the genetic mechanisms associated with complex diseases, including macular degeneration, diabetes mellitus, type 2, heart disease, and cancer, molecular genetic approaches to psychiatric illness have met with more limited success. While factors such as small allelic effects, allelic heterogeneity, and variation in population substructure have received considerable attention in attempt to explain the paucity of significant results in psychiatric genetics, significantly less focus has been directed toward phenotypic factors.

METHOD

Data derived from molecular genetic studies of the psychosis phenotype in patients with a range of psychiatric illnesses are reviewed.

RESULTS

Available data suggest that genes do not respect the boundaries of the current diagnostic system but may confer risk for symptom-based phenotypic variation that traverses those boundaries.

CONCLUSIONS

Molecular genetic studies offer convincing evidence for a relation between genetic variation and symptom-based phenotypic variation within psychiatric illness. These data may provide novel insights into the pathophysiology of schizophrenia and other related disorders. The exploration of relations between genetic variation and symptom variation that traverses traditional diagnostic boundaries may ultimately lead to more refined classification systems that more closely reflect the genetic etiology of psychiatric illness.

Aggregated proteins in schizophrenia and other chronic mental diseases: DISC1opathies

Chronic mental diseases (CMD) like the schizophrenias are progressive diseases of heterogenous but poorly understood biological origin. An imbalance in proteostasis is a hallmark of dysfunctional neurons, leading to impaired clearance and abnormal deposition of protein aggregates. Thus, it can be hypothesized that unbalanced proteostasis in such neurons may also lead to protein aggregates in schizophrenia. These protein aggregates, however, would be more subtle then in the classical neurodegenerative diseases and as such have not yet been detected. The DISC1 (Disrupted-in-schizophrenia 1) gene is considered among the most promising candidate genes for CMD having been identified as linked to CMD in a Scottish pedigree and having since been found to associate to various phenotypes of CMD. We have recently demonstrated increased insoluble DISC1 protein in the cingular cortex in approximately 20% of cases of CMD within the widely used Stanley Medical Research Institute Consortium Collection. Surprisingly, in vitro, DISC1 aggregates were cell-invasive, i.e., purified aggresomes or recombinant DISC1 fragments where internalized at an efficiency comparable to that of α-synuclein. Intracellular DISC1 aggresomes acquired gain-of-function properties in recruiting otherwise soluble proteins such as the candidate schizophrenia protein dysbindin. Disease-associated DISC1 polymorphism S704C led to a higher oligomerization tendency of DISC1. These findings justify classification of DISC1-dependent brain disorders as protein conformational disorders which we have tentatively termed DISC1opathies. The notion of disturbed proteostasis and protein aggregation as a mechanism of mental diseases is thus emerging. The yet unidentified form of neuronal impairment in CMD is more subtle than in the classical neurodegenerative diseases without leading to massive cell death and as such present a different kind of neuronal dysfunctionality, eventually confined to highly selective CNS subpopulations.

DISC1 and Striatal Volume: A Potential Risk Phenotype For mental Illness

Disrupted-in-schizophrenia 1 was originally discovered in a large Scottish family with abnormally high rates of severe mental illness, including schizophrenia, bipolar disorder, and depression. An accumulating body of evidence from genetic, postmortem, and animal data supports a role for DISC1 in different forms of mental illness. DISC1 may play an important role in determining structure and function of several brain regions. One brain region of particular importance for several mental disorders is the striatum, and DISC1 mutant mice have demonstrated an increase in dopamine (D2) receptors in this structure. However, association between DISC1 functional polymorphisms and striatal structure have not been examined in humans. We, therefore hypothesized that there would be a relationship between human striatal volume and DISC1 genotype, specifically in the Leu607Phe (rs6675281) and Ser704Cys (rs821618) single nucleotide polymorphisms. We tested our hypothesis by automatically identifying the striatum in 54 healthy volunteers recruited for this study. We also performed an exploratory analysis of cortical thickness, cortical surface area, and structure volume. Our results demonstrate that Phe allele carriers have larger striatal volume bilaterally (left striatum: p = 0.017; right striatum: p = 0.016). From the exploratory analyses we found that the Phe carriers also had larger left hemisphere volumes (p = 0.0074) and right occipital lobe surface area (p = 0.014) compared to LeuLeu homozygotes. However, these exploratory findings do not survive a conservative correction for multiple comparisons. Our findings demonstrate that a functional DISC1 variant influences striatal volumes. Taken together with animal data that this gene influences D2 receptor levels in striatum, a key risk pathway for mental illnesses such as schizophrenia and bipolar disorder may be conferred via DISC1's effects on the striatum.

DISC1 Pathway in Brain Development: Exploring Therapeutic Targets for Major Psychiatric Disorders

Genetic risk factors for major psychiatric disorders play key roles in neurodevelopment. Thus, exploring the molecular pathways of risk genes is important not only for understanding the molecular mechanisms underlying brain development, but also to decipher how genetic disturbances affect brain maturation and functioning relevant to major mental illnesses. During the last decade, there has been significant progress in determining the mechanisms whereby risk genes impact brain development. Nonetheless, given that the majority of psychiatric disorders have etiological complexities encompassing multiple risk genes and environmental factors, the biological mechanisms of these diseases remain poorly understood. How can we move forward to our research for discovery of the biological markers and novel therapeutic targets for major mental disorders? Here we review recent progress in the neurobiology of disrupted in schizophrenia 1 (DISC1), a major risk gene for major mental disorders, with a particular focus on its roles in cerebral cortex development. Convergent findings implicate DISC1 as part of a large, multi-step pathway implicated in various cellular processes and signal transduction. We discuss links between the DISC1 pathway and environmental factors, such as immune/inflammatory responses, which may suggest novel therapeutic targets. Existing treatments for major mental disorders are hampered by a limited number of pharmacological targets. Consequently, elucidation of the DISC1 pathway, and its association with neuropsychiatric disorders, may offer hope for novel treatment interventions.

DISC1: Structure, Function, and Therapeutic Potential for Major Mental Illness

Disrupted in schizophrenia 1 (DISC1) is well established as a genetic risk factor across a spectrum of psychiatric disorders, a role supported by a growing body of biological studies, making the DISC1 protein interaction network an attractive therapeutic target. By contrast, there is a relative deficit of structural information to relate to the myriad biological functions of DISC1. Here, we critically appraise the available bioinformatics and biochemical analyses on DISC1 and key interacting proteins, and integrate this with the genetic and biological data. We review, analyze, and make predictions regarding the secondary structure and propensity for disordered regions within DISC1, its protein-interaction domains, subcellular localization motifs, and the structural and functional implications of common and ultrarare DISC1 variants associated with major mental illness. We discuss signaling pathways of high pharmacological potential wherein DISC1 participates, including those involving phosphodiesterase 4 (PDE4) and glycogen synthase kinase 3 (GSK3). These predictions and priority areas can inform future research in the translational and potentially guide the therapeutic processes.

Impact of DISC1 variation on neuroanatomical and neurocognitive phenotypes

Although disrupted in schizophrenia 1 (DISC1) has been implicated in many psychiatric disorders, including schizophrenia, bipolar disorder, schizoaffective disorder and major depression, its biological role in these disorders is unclear. To better understand this gene and its role in psychiatric disease, we conducted transcriptional profiling and genome-wide association analysis in 1232 pedigreed Mexican-American individuals for whom we have neuroanatomic images, neurocognitive assessments and neuropsychiatric diagnoses. SOLAR was used to determine heritability, identify gene expression patterns and perform association analyses on 188 quantitative brain-related phenotypes. We found that the DISC1 transcript is highly heritable (h(2)=0.50; P=1.97 × 10(-22)), and that gene expression is strongly cis-regulated (cis-LOD=3.89) but is also influenced by trans-effects. We identified several DISC1 polymorphisms that were associated with cortical gray matter thickness within the parietal, temporal and frontal lobes. Associated regions affiliated with memory included the entorhinal cortex (rs821639, P=4.11 × 10(-5); rs2356606, P=4.71 × 10(-4)), cingulate cortex (rs16856322, P=2.88 × 10(-4)) and parahippocampal gyrus (rs821639, P=4.95 × 10(-4)); those affiliated with executive and other cognitive processing included the transverse temporal gyrus (rs9661837, P=5.21 × 10(-4); rs17773946, P=6.23 × 10(-4)), anterior cingulate cortex (rs2487453, P=4.79 × 10(-4); rs3738401, P=5.43 × 10(-4)) and medial orbitofrontal cortex (rs9661837; P=7.40 × 10(-4)). Cognitive measures of working memory (rs2793094, P=3.38 × 10(-4)), as well as lifetime history of depression (rs4658966, P=4.33 × 10(-4); rs12137417, P=4.93 × 10(-4)) and panic (rs12137417, P=7.41 × 10(-4)) were associated with DISC1 sequence variation. DISC1 has well-defined genetic regulation and clearly influences important phenotypes related to psychiatric disease.

Common functional polymorphisms of DISC1 and cortical maturation in typically developing children and adolescents

Disrupted-in-schizophrenia-1 (DISC1), contains two common non-synonymous single-nucleotide polymorphisms (SNPs)--Leu607Phe and Ser704Cys--that modulate (i) facets of DISC1 molecular functioning important for cortical development, (ii) fronto-temporal cortical anatomy in adults and (iii) risk for diverse psychiatric phenotypes that often emerge during childhood and adolescence, and are associated with altered fronto-temporal cortical development. It remains unknown, however, if Leu607Phe and Ser704Cys influence cortical maturation before adulthood, and whether each SNP shows unique or overlapping effects. Therefore, we related genotype at Leu607Phe and Ser704Cys to cortical thickness (CT) in 255 typically developing individuals aged 9-22 years on whom 598 magnetic resonance imaging brain scans had been acquired longitudinally. Rate of cortical thinning varied with DISC1 genotype. Specifically, the rate of cortical thinning was attenuated in Phe-carrier compared with Leu-homozygous groups (in bilateral superior frontal and left angular gyri) and accelerated in Ser-homozygous compared with Cys-carrier groups (in left anterior cingulate and temporal cortices). Both SNPs additively predicted fixed differences in right lateral temporal CT, which were maximal between Phe-carrier/Ser-homozygous (thinnest) vs Leu-homozygous/Cys-carrier (thickest) groups. Leu607Phe and Ser704Cys genotype interacted to predict the rate of cortical thinning in right orbitofrontal, middle temporal and superior parietal cortices, wherein a significantly reduced rate of CT loss was observed in Phe-carrier/Cys-carrier participants only. Our findings argue for further examination of Leu607Phe and Ser704Cys interactions at a molecular level, and suggest that these SNPs might operate (in concert with other genetic and environmental factors) to shape risk for diverse phenotypes by impacting on the early maturation of fronto-temporal cortices.

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

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

Sequencing of DISC1 pathway genes reveals increased burden of rare missense variants in schizophrenia patients from a northern Swedish population

In recent years, DISC1 has emerged as one of the most credible and best supported candidate genes for schizophrenia and related neuropsychiatric disorders. Furthermore, increasing evidence--both genetic and functional--indicates that many of its protein interaction partners are also involved in the development of these diseases. In this study, we applied a pooled sample 454 sequencing strategy, to explore the contribution of genetic variation in DISC1 and 10 of its interaction partners (ATF5, Grb2, FEZ1, LIS-1, PDE4B, NDE1, NDEL1, TRAF3IP1, YWHAE, and ZNF365) to schizophrenia susceptibility in an isolated northern Swedish population. Mutation burden analysis of the identified variants in a population of 486 SZ patients and 514 control individuals, revealed that non-synonymous rare variants with a MAF<0.01 were significantly more present in patients compared to controls (8.64% versus 4.7%, P = 0.018), providing further evidence for the involvement of DISC1 and some of its interaction partners in psychiatric disorders. This increased burden of rare missense variants was even more striking in a subgroup of early onset patients (12.9% versus 4.7%, P = 0.0004), highlighting the importance of studying subgroups of patients and identifying endophenotypes. Upon investigation of the potential functional effects associated with the identified missense variants, we found that ∼90% of these variants reside in intrinsically disordered protein regions. The observed increase in mutation burden in patients provides further support for the role of the DISC1 pathway in schizophrenia. Furthermore, this study presents the first evidence supporting the involvement of mutations within intrinsically disordered protein regions in the pathogenesis of psychiatric disorders. As many important biological functions depend directly on the disordered state, alteration of this disorder in key pathways may represent an intriguing new disease mechanism for schizophrenia and related neuropsychiatric diseases. Further research into this unexplored domain will be required to elucidate the role of the identified variants in schizophrenia etiology.

DISC1 exon 11 rare variants found more commonly in schizoaffective spectrum cases than controls

We previously performed a linkage study using families identified through probands meeting criteria for DSM-IV schizoaffective disorder, bipolar type (SABP) and observed a genome-wide significant signal (LOD = 3.54) at chromosome 1q42 close to DISC1. An initial sequencing study of DISC1 using 14 unrelated DSM-IV SABP samples from the linkage study identified 2 non-synonymous coding SNPs in exon 11 in 2 separate individuals. Here we provide evidence of additional rare coding SNPs within exon 11. In sequencing exon 11 in 506 cases and 1,211 controls for variants that occurred only once, 4 additional rare variants were found in cases (P-value = 0.008, Fisher's exact trend test).

The effects of DISC1 risk variants on brain activation in controls, patients with bipolar disorder and patients with schizophrenia

Three risk variants (rs1538979, rs821577, and rs821633) in the Disrupted-in-Schizophrenia-1 (DISC1) gene have previously been associated with both schizophrenia and bipolar disorder in a recent collaborative analysis of European cohorts. In this study we examined the effects of these risk variants on brain activation during functional magnetic resonance imaging (fMRI) of the Hayling Sentence Completion Task (HSCT) in healthy volunteers (n=33), patients with schizophrenia (n=20) and patients with bipolar disorder (n=36). In the healthy controls the risk associated allele carriers of SNPs rs1538979 and rs821633 demonstrated decreased activation of the cuneus. Moreover, there was an effect of SNP rs1538979 in the pre/postcentral gyrus with decreased activation in healthy controls and increased activation in patients with schizophrenia. In the bipolar group there was decreased activation in the risk carriers of SNP rs821633 in the inferior parietal lobule and left cingulate cortex. Clusters in the precentral gyrus, left middle temporal gyrus and left cerebellum were found to be significant on examining the group × genotype interactions. These findings may provide a better understanding of the neural effects of DISC1 variants and on the pathophysiology of schizophrenia and bipolar disorder.

Association study between Disrupted-in-Schizophrenia-1 (DISC1) and Japanese patients with treatment-resistant schizophrenia (TRS)

Treating the 20-30% of patients with schizophrenia whose symptoms are resistant to antipsychotic treatment, a condition known as treatment-resistant schizophrenia (TRS), can be problematic. Recently, an association between Disrupted-in-Schizophrenia-1 (DISC1), a candidate susceptibility gene for schizophrenia, and TRS was reported. Associations between three missense SNPs, rs3738401 (Q264R), rs6675281 (L607F), and rs821616 (S704C) in DISC1, especially rs3738401, showed strong significance. Thus, the main aim of our current study was to examine if the reported possible functional polymorphisms in DISC1 were related to Japanese TRS. First, DISC1 was re-investigated in 485 Japanese patients with schizophrenia and 660 healthy controls with a case-control study using four candidate SNPs, rs751229, rs3738401, rs821597, and rs821616. DISC1 was not associated with schizophrenia in the Japanese population. Second, we investigated whether these SNPs contributed to TRS in 127 inpatients with schizophrenia (35 patients; TRS and 92 patients; non-TRS). The genotypic distributions of these four SNPs were not significantly different between TRS and non-TRS in either genotypic or recessive models of minor alleles. In addition, clinical variables, such as improvement in clinical symptoms, duration of hospitalization, and total antipsychotics dose amounts, were not different among the genotypes of these SNPs. Taken together, results showed that DISC1 had no apparent degree of association with Japanese patients with schizophrenia as a candidate susceptibility gene for disease per se or TRS.

Neuroplasticity signaling pathways linked to the pathophysiology of schizophrenia

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

No association of Disrupted-in-Schizophrenia-1 variation with prefrontal function in patients with schizophrenia and bipolar disorder

The Disrupted-in-Schizophrenia-1 (DISC1) gene has been implicated in both schizophrenia and bipolar disorder by linkage and genetic association studies. Altered prefrontal cortical function is a pathophysiological feature of both disorders, and we have recently shown that variation in DISC1 modulates prefrontal activation in healthy volunteers. Our goal was to examine the influence of the DISC1 polymorphism Cys704Ser on prefrontal function in schizophrenia and bipolar disorder. From 2004 to 2008, patients with schizophrenia (N = 44), patients with bipolar disorder (N = 35) and healthy volunteers (N = 53) were studied using functional magnetic resonance imaging while performing a verbal fluency task. The effect of Cys704Ser on cortical activation was compared between groups as Cys704 carriers vs. Ser704 homozygotes. In contrast to the significant effect on prefrontal activation we had previously found in healthy subjects, no significant effect of Cys704Ser was detected in this or any other region in either the schizophrenia or bipolar groups. When controls were compared with patients with schizophrenia, there was a diagnosis by genotype interaction in the left middle/superior frontal gyrus [family-wise error (FWE) P = 0.002]. In this region, Ser704/ser704 controls activated more than Cys704 carriers, and there was a trend in the opposite direction in schizophrenia patients. In contrast to its effect in healthy subjects, variation in DISC1 Cys704Ser704 genotype was not associated with altered prefrontal activation in patients with schizophrenia or bipolar disorder. The absence of an effect in patients may reflect interactions of the effects of DISC1 genotype with the effects of other genes associated with these disorders, and/or with the effects of the disorders on brain function.

Between destiny and disease: genetics and molecular pathways of human central nervous system aging

Aging of the human brain is associated with "normal" functional, structural, and molecular changes that underlie alterations in cognition, memory, mood and motor function, amongst other processes. Normal aging also imposes a robust constraint on the onset of many neurological diseases, ranging from late onset neurodegenerative diseases, such as Alzheimer's (AD) and Parkinson's diseases (PD), to early onset psychiatric disorders, such as bipolar disorder (BPD) and schizophrenia (SCZ). The molecular mechanisms and genetic underpinnings of age-related changes in the brain are understudied, and, while they share some overlap with peripheral mechanisms of aging, many are unique to the largely non-mitotic brain. Hence, understanding mechanisms of brain aging and identifying associated modulators may have profound consequences for the prevention and treatment of age-related impairments and diseases. Here we review current knowledge on age-related functional and structural changes, their molecular and genetic underpinnings, and discuss how these pathways may contribute to the vulnerability to develop age-related neurological diseases. We highlight recent findings from human post-mortem brain microarray studies, which we hypothesize, point to a potential genetically controlled transcriptional program underlying molecular changes and age-gating of neurological diseases. Finally, we discuss the implications of this model for understanding basic mechanisms of brain aging and for the future investigation of therapeutic approaches.

The DISC1 Ser704Cys substitution affects centrosomal localization of its binding partner PCM1 in glia in human brain

Disrupted-in-schizophrenia 1 (DISC1) has been genetically associated with schizophrenia, and with brain phenotypes including grey matter volume and working memory performance. However, the molecular and cellular basis for these associations remains to be elucidated. One potential mechanism may be via an altered interaction of DISC1 with its binding partners. In this context, we previously demonstrated that one DISC1 variant, Leu607Phe, influenced the extent of centrosomal localization of pericentriolar material 1 (PCM1) in SH-SY5Y cells. The current study extends this work to human brain, and includes another DISC1 coding variant, Ser704Cys. Using immunohistochemistry, we first characterized the distribution of PCM1 in human superior temporal gyrus (STG). PCM1 immunoreactivity was localized to the centrosome in glia, but not in neurons, which showed widespread immunoreactivity. We quantified centrosomal PCM1 immunoreactivity in STG glia of 81 controls and 67 subjects with schizophrenia, genotyped for the two polymorphisms. Centrosomal PCM1 immunoreactive area was smaller in Cys704 carriers than in Ser704 homozygotes, with a similar trend in Phe607 homozygotes compared with Leu607 carriers, replicating the finding in SH-SY5Y cells. No differences were seen between controls and subjects with schizophrenia. These findings confirm in vivo that DISC1 coding variants modulate centrosomal PCM1 localization, highlight a role for DISC1 in glial function and provide a possible cellular mechanism contributing to the association of these DISC1 variants with psychiatric phenotypes. Whether this influence of DISC1 genotype extends to other centrosomal proteins and DISC1 binding partners remains to be determined.

Oligomer assembly of the C-terminal DISC1 domain (640-854) is controlled by self-association motifs and disease-associated polymorphism S704C

Genetic studies have established a role of disrupted-in-schizophrenia-1 (DISC1) in chronic mental diseases (CMD). Limited experimental data are available on the domain structure of the DISC1 protein although multiple interaction partners are known including a self-association domain within the middle part of DISC1 (residues 403-504). The DISC1 C-terminal domain is deleted in the original Scottish pedigree where DISC1 harbors two coiled-coil domains and disease-associated polymorphisms at 607 and 704, as well as the important nuclear distribution element-like 1 (NDEL1) binding site at residues 802-839. Here, we performed mutagenesis studies of the C-terminal domain of the DISC1 protein (residues 640-854) and analyzed the expressed constructs by biochemical and biophysical methods. We identified novel DISC1 self-association motifs and the necessity of their concerted action for orderly assembly: the region 765-854 comprising a coiled-coil domain is a dimerization domain and the region 668-747 an oligomerization domain; dimerization was found to be a prerequisite for orderly assembly of oligomers. Consistent with this, disease-associated polymorphism C704 displayed a slightly higher oligomerization propensity. The heterogeneity of DISC1 multimers in vitro was confirmed with a monoclonal antibody binding exclusively to HMW multimers. We also identified C-terminal DISC1 fragments in human brains, suggesting that C-terminal fragments could carry out DISC1-dependent functions. When the DISC1 C-terminal domain was transiently expressed in cells, it assembled into a range of soluble and insoluble multimers with distinct fractions selectively binding NDEL1, indicating functionality. Our results suggest that assembly of the C-terminal domain is controlled by distinct domains including the disease-associated polymorphism 704 and is functional in vivo.

DISC1 association, heterogeneity and interplay in schizophrenia and bipolar disorder

Disrupted in schizophrenia 1 (DISC1) has been associated with risk of schizophrenia, schizoaffective disorder, bipolar disorder, major depression, autism and Asperger syndrome, but apart from in the original translocation family, true causal variants have yet to be confirmed. Here we report a harmonized association study for DISC1 in European cohorts of schizophrenia and bipolar disorder. We identify regions of significant association, demonstrate allele frequency heterogeneity and provide preliminary evidence for modifying interplay between variants. Whereas no associations survived permutation analysis in the combined data set, significant corrected associations were observed for bipolar disorder at rs1538979 in the Finnish cohorts (uncorrected P=0.00020; corrected P=0.016; odds ratio=2.73+/-95% confidence interval (CI) 1.42-5.27) and at rs821577 in the London cohort (uncorrected P=0.00070; corrected P=0.040; odds ratio=1.64+/-95% CI 1.23-2.19). The rs821577 single nucleotide polymorphism (SNP) showed evidence for increased risk within the combined European cohorts (odds ratio=1.27+/-95% CI 1.07-1.51), even though significant corrected association was not detected (uncorrected P=0.0058; corrected P=0.28). After conditioning the European data set on the two risk alleles, reanalysis revealed a third significant SNP association (uncorrected P=0.00050; corrected P=0.025). This SNP showed evidence for interplay, either increasing or decreasing risk, dependent upon the presence or absence of rs1538979 or rs821577. These findings provide further support for the role of DISC1 in psychiatric illness and demonstrate the presence of locus heterogeneity, with the effect that clinically relevant genetic variants may go undetected by standard analysis of combined cohorts.

Association between genes of Disrupted in schizophrenia 1 (DISC1) interactors and schizophrenia supports the role of the DISC1 pathway in the etiology of major mental illnesses

BACKGROUND

Disrupted in Schizophrenia 1 (DISC1) is currently one of the most interesting candidate genes for major mental illness, having been demonstrated to associate with schizophrenia, bipolar disorder, major depression, autism, and Asperger's syndrome. We have previously reported a DISC1 haplotype, HEP3, and an NDE1 spanning tag haplotype to associate to schizophrenia in Finnish schizophrenia families. Because both DISC1 and NDE1 display association in our study sample, we hypothesized that other genes interacting with DISC1 might also have a role in the etiology of schizophrenia.

METHODS

We selected 11 additional genes encoding components of the "DISC1 pathway" and studied these in our study sample of 476 families including 1857 genotyped individuals. We performed single nucleotide polymorphism (SNP) and haplotype association analyses in two independent sets of families. For markers and haplotypes found to be consistently associated in both sets, the overall significance was tested with the combined set of families.

RESULTS

We identified three SNPs to be associated with schizophrenia in PDE4D (rs1120303, p = .021), PDE4B (rs7412571, p = .018), and NDEL1 (rs17806986, p = .0038). Greater significance was observed with allelic haplotypes of PDE4D (p = .00084), PDE4B (p = .0022 and p = .029), and NDEL1 (p = .0027) that increased or decreased schizophrenia susceptibility.

CONCLUSIONS

Our findings with other converging lines of evidence support the underlying importance of DISC1-related molecular pathways in the etiology of schizophrenia and other major mental illnesses.

Research review: crossing syndrome boundaries in the search for brain endophenotypes

The inherent imprecision of behavioral phenotyping is the single most important factor contributing to the failure to discover the biological factors that are involved in psychiatric and neurodevelopmental disorders (e.g., Bearden & Freimer, 2006). In this review article we argue that in addition to an appreciation of the inherent complexity at the biological level, a rather urgent task facing behavioral scientists involves a reconsideration of the role that clinical syndromes play in psychological theorizing, as well as in research into the biological basis of cognition and personality. Syndrome heterogeneity, cross-syndrome similarities and syndrome comorbidities question the relevance of syndromes to biological research. It is suggested that the search for brain endophenotypes, intermediate between genes and behavior, should be based on cross-syndrome, trait classification. Cohort selection should rest on behavioral homogeneity, enabling, when necessary, syndrome heterogeneity.

The Disrupted-in-Schizophrenia-1 Ser704Cys polymorphism and brain morphology in schizophrenia

The Disrupted-in-Schizophrenia-1 (DISC1) polymorphism is a strong candidate for a schizophrenia-susceptibility gene as it is widely expressed in cortical and limbic regions, but the effect of its genotype variation on brain morphology in schizophrenia is not well known. This study examined the association between the DISC1 Ser704Cys polymorphism and volumetric measurements for a broad range of fronto-parietal, temporal, and limbic-paralimbic regions using magnetic resonance imaging in a Japanese sample of 33 schizophrenia patients and 29 healthy comparison subjects. The Cys carriers had significantly larger volumes of the medial superior frontal gyrus and short insular cortex than the Ser homozygotes only for healthy comparison subjects. The Cys carriers tended to have a smaller supramarginal gyrus than the Ser homozygotes in schizophrenia patients, but not in healthy comparison subjects. The right medial superior frontal gyrus volume was significantly correlated with daily dosage of antipsychotic medication in Ser homozygote schizophrenia patients. These different genotype effects of the DISC1 Ser704Cys polymorphism on the brain morphology in schizophrenia patients and healthy comparison subjects suggest that variation in the DISC1 gene might be, at least partly, involved in the neurobiology of schizophrenia. Our findings also suggest that the DISC1 genotype variation might have some relevance to the medication effect on brain morphology in schizophrenia.

Association of the SerCys DISC1 polymorphism with human hippocampal formation gray matter and function during memory encoding

A common nonsynonymous single nucleotide polymorphism leading to a serine-to-cysteine substitution at amino acid 704 (Ser(704)Cys) in the DISC1 protein sequence has been recently associated with schizophrenia and with specific hippocampal abnormalities. Here, we used multimodal neuroimaging to investigate in a large sample of healthy subjects the putative association of the Ser(704)Cys DISC1 polymorphism with in vivo brain phenotypes including hippocampal formation (HF) gray matter volume and function (as assessed with functional MRI) as well as HF functional coupling with the neural network engaged during encoding of recognition memory. Individuals homozygous for DISC1 Ser allele relative to carriers of the Cys allele showed greater gray matter volume in the HF. Further, Ser/Ser subjects exhibited greater engagement of the HF together with greater HF-dorsolateral prefrontal cortex functional coupling during memory encoding, in spite of similar behavioral performance. These findings consistently support the notion that Ser(704)Cys DISC1 polymorphism is physiologically relevant. Moreover, they support the hypothesis that genetic variation in DISC1 may affect the risk for schizophrenia by modifying hippocampal gray matter and function.

Association of variants in DISC1 with psychosis-related traits in a large population cohort

CONTEXT

There is an abundance of data from human genetic studies and animal models that implies a role for the disrupted in schizophrenia 1 gene (DISC1) in the etiology of schizophrenia and other major mental illnesses.

OBJECTIVE

To study the effect of previously identified risk alleles of DISC1 on quantitative intermediate phenotypes for psychosis in an unselected population.

DESIGN

We examined 41 single-nucleotide polymorphisms within DISC1 and performed tests of association with 4 quantitative phenotypes.

SETTING

Academic research.

PARTICIPANTS

Individuals from an unselected birth cohort in Finland. Originally, everyone born in the catchment area in 1966 (N = 12 058) was included in the study. Of these, 4651 (38.6%) attended the 31-year follow-up and could be included in the study.

MAIN OUTCOME MEASURES

Scores on 4 psychometric instruments selected to function as proxies for positive and negative aspects of psychotic disorders, including the Perceptual Aberration Scale, Revised Social Anhedonia Scale, Revised Physical Anhedonia Scale, and Schizoidia Scale by Golden and Meehl.

RESULTS

Carriers of the minor allele of marker rs821577 had significantly higher scores on social anhedonia (P < .001). The minor allele of marker rs821633 was strongly associated with lower scores on social anhedonia when analyzed dependent on the absence of the minor alleles of markers rs1538979 and rs821577 (P < .001).

CONCLUSIONS

Variants in DISC1 affect the level of social anhedonia, a cardinal symptom of schizophrenia in the general population. DISC1 might be more central to human psychological functioning than previously thought, as it seems to affect the degree to which people enjoy social interactions.

Neurobiology of cognitive aging: insights from imaging genetics

Over the last several years, neuroscientists have been increasingly using neuroimaging techniques to unravel the neurobiology underlying cognitive aging, and in more recent years to explore the role of genes on the variability of the aging process. One of the primary goals of this research is to identify proteins involved in cognitive aging with the hope that this would facilitate the development of novel treatments to combat cognitive impairment. Further, it is likely with early identification of susceptible individuals, early intervention through life-style changes and other methods could increase an individual's resilience to the effects of aging.

Elucidating the relationship between DISC1, NDEL1 and NDE1 and the risk for schizophrenia: evidence of epistasis and competitive binding

DISC1 influences susceptibility to psychiatric disease and related phenotypes. Intact functions of DISC1 and its binding partners, NDEL1 and NDE1, are critical to neurodevelopmental processes aberrant in schizophrenia (SZ). Despite evidence of an NDEL1-DISC1 protein interaction, there have been no investigations of the NDEL1 gene or the relationship between NDEL1 and DISC1 in SZ. We genotyped six NDEL1 single-nucleotide polymorphisms (SNPs) in 275 Caucasian SZ patients and 200 controls and tested for association and interaction between the functional SNP Ser704Cys in DISC1 and NDEL1. We also evaluated the relationship between NDE1 and DISC1 genotype and SZ. Finally, in a series of in vitro assays, we determined the binding profiles of NDEL1 and NDE1, in relation to DISC1 Ser704Cys. We observed a single haplotype block within NDEL1; the majority of variation was captured by NDEL1 rs1391768. We observed a significant interaction between rs1391768 and DISC1 Ser704Cys, with the effect of NDEL1 on SZ evident only against the background of DISC1 Ser704 homozygosity. Secondary analyses revealed no direct relationship between NDE1 genotype and SZ; however, there was an opposite pattern of risk for NDE1 genotype when conditioned on DISC1 Ser704Cys, with NDE1 rs3784859 imparting a significant effect but only in the context of a Cys-carrying background. In addition, we report opposing binding patterns of NDEL1 and NDE1 to Ser704 versus Cys704, at the same DISC1 binding domain. These data suggest that NDEL1 significantly influences risk for SZ via an interaction with DISC1. We propose a model where NDEL1 and NDE1 compete for binding with DISC1.