The genetics and biology of DISC1--an emerging role in psychosis and cognition.

In the developing field of biological psychiatry, DISC1 stands out by virtue of there being credible evidence, both genetic and biological, for a role in determining susceptibility to schizophrenia and related disorders. We highlight the methodologic paradigm that led to identification of DISC1 and review the supporting genetic and biological evidence. The original finding of DISC1 as a gene disrupted by a balanced translocation on chromosome 1q42 that segregates with schizophrenia, bipolar disorder, and recurrent major depression has sparked a number of confirmatory linkage and association studies. These indicate that DISC1 is a generalizable genetic risk factor for psychiatric illness that also influences cognition in healthy subjects. DISC1 has also been shown to interact with a number of proteins with neurobiological pedigrees, including Ndel1 (NUDEL), a key regulator of neuronal migration with endo-oligopeptidase activity, and PDE4B, a phosphodiesterase that is critical for cyclic adenosine monophosphate signaling and that is directly linked to learning, memory, and mood. Both are potential "drug" targets. DISC1 has thus emerged as a key molecular player in the etiology of major mental illness and in normal brain processes.     

DISC1 in schizophrenia: genetic mouse models and human genomic imaging

Schizophrenia and related disorders have a major genetic component. Several large-scale studies have uncovered a number of possible candidate genes, but these have yet to be consistently replicated and their underlying biological function remains elusive. One exception is 'Disrupted in schizophrenia 1' (DISC1), a gene locus originally identified in a large Scottish family, showing a heavy burden of major mental illnesses associated with a balanced t(1;11)(q42.1;q14.3) chromosome translocation. Substantial genetic and biological research on DISC1 has been reported in the intervening 10 years: DISC1 is now recognized as a genetic risk factor for a spectrum of psychiatric disorders and DISC1 impacts on many aspects of central nervous system (CNS) function, including neurodevelopment, neurosignaling, and synaptic functioning. Evidence has emerged from genetic studies showing a relationship between DISC1 and quantitative traits, including working memory, cognitive aging, gray matter volume in the prefrontal cortex, and abnormalities in hippocampal structures and function. DISC1 interacts with numerous proteins also involved in neuronal migration, neurite outgrowth, cytoskeletal modulation, and signal transduction, some of which have been reported as independent genetic susceptibility factors for psychiatric morbidity. Here, we focus on the growing literature relating genetic variation in the DISC1 pathway to functional and structural studies of the brain in humans and in the mouse.     

A review of Disrupted-In-Schizophrenia-1 (DISC1): neurodevelopment, cognition, and mental conditions.

Disrupted-In-Schizophrenia-1 (DISC1) is a promising candidate gene for schizophrenia (SZ) and bipolar disorder (BP), but its basic biology remains to be elucidated. Accumulating genetic evidence supports that DISC1 is associated with some aspects of cognitive functions relevant to SZ and BP. Here, we provide a summary of the current updates in biological studies of DISC1. Disrupted-In-Schizophrenia-1, preferentially expressed in the forebrain, has multiple isoforms with potential posttranslational modifications. Disrupted-In-Schizophrenia-1 protein occurs in multiple subcellular compartments, which include the centrosome, microtubule fractions, postsynaptic densities, actin cytoskeletal fractions, the mitochondria, and the nucleus. Recent studies have clarified that DISC1 mediates at least centrosome-dynein cascade and cyclic adenosine monophosphate (cAMP) signaling. Furthermore, both cytogenetic and cell biological studies consistently suggest that an overall loss of DISC1 function (either haploinsufficiency or dominant-negative, or both) may be associated with SZ and BP. On the basis of these findings, production of DISC1 genetically engineered mice is proposed as a promising animal model for SZ and BP. Several groups are currently generating DISC1 mice and starting to characterize them. In this review, the advantages and disadvantages of each animal model are discussed.     

The DISC locus in psychiatric illness

The DISC locus is located at the breakpoint of a balanced t(1;11) chromosomal translocation in a large and unique Scottish family. This translocation segregates in a highly statistically significant manner with a broad diagnosis of psychiatric illness, including schizophrenia, bipolar disorder and major depression, as well as with a narrow diagnosis of schizophrenia alone. Two novel genes were identified at this locus and due to the high prevalence of schizophrenia in this family, they were named Disrupted-in-Schizophrenia-1 (DISC1) and Disrupted-in-Schizophrenia-2 (DISC2). DISC1 encodes a novel multifunctional scaffold protein, whereas DISC2 is a putative noncoding RNA gene antisense to DISC1. A number of independent genetic linkage and association studies in diverse populations support the original linkage findings in the Scottish family and genetic evidence now implicates the DISC locus in susceptibility to schizophrenia, schizoaffective disorder, bipolar disorder and major depression as well as various cognitive traits. Despite this, with the exception of the t(1;11) translocation, robust evidence for a functional variant(s) is still lacking and genetic heterogeneity is likely. Of the two genes identified at this locus, DISC1 has been prioritized as the most probable candidate susceptibility gene for psychiatric illness, as its protein sequence is directly disrupted by the translocation. Much research has been undertaken in recent years to elucidate the biological functions of the DISC1 protein and to further our understanding of how it contributes to the pathogenesis of schizophrenia. These data are the main subject of this review; however, the potential involvement of DISC2 in the pathogenesis of psychiatric illness is also discussed. A detailed picture of DISC1 function is now emerging, which encompasses roles in neurodevelopment, cytoskeletal function and cAMP signalling, and several DISC1 interactors have also been defined as independent genetic susceptibility factors for psychiatric illness. DISC1 is a hub protein in a multidimensional risk pathway for major mental illness, and studies of this pathway are opening up opportunities for a better understanding of causality and possible mechanisms of intervention.     

How has DISC1 enabled drug discovery?

Growing genetic and clinical evidence has shown that disrupted-in-schizophrenia 1 (DISC1) is one of the most compelling risk genes for schizophrenia and other major mental disorders. The understanding of the role that DISC1 plays in neuronal development and cell signaling has been greatly enhanced by the identification of DISC1 binding partners, an appreciation of its expression during development and functional studies using RNA interference. But what is the impact of this explosion of data for psychiatric drug discovery? Though we are at a very early stage of our understanding of DISC1 biology, it is an important time to review what has already been achieved and to discuss its impact. DISC1 biology has enabled the identification of new therapeutic targets in the form of DISC1 binding partners and other molecules found within a large DISC1 interaction network, the so-called 'DISC1 interactome'. We will review the better characterized of these interactions and also emphasize the richness of potential targets in the more poorly studied areas of the interactome. Furthermore, DISC1 has encouraged the development of new animal models for psychiatric disorders, which is critical for the study of disease biology. Thus, DISC1 may have the potential to not only point us in the direction of novel drug targets but also provide more relevant animal models for compound testing.     

Genes and schizophrenia: beyond schizophrenia: the role of DISC1 in major mental illness

Schizophrenia and related disorders have a major genetic component, but despite much effort and many claims, few genes have been consistently replicated and fewer have biological support. One recent exception is "Disrupted in Schizophrenia 1" (DISC1), which was identified at the breakpoint on chromosome 1 of the balanced translocation (1;11)(q42.1;q14.3) that co-segregated in a large Scottish family with a wide spectrum of major mental illnesses. Since then, genetic analysis has implicated DISC1 in schizophrenia, schizoaffective disorder, bipolar affective disorder, and major depression. Importantly, evidence is emerging from genetic studies for a causal relationship between DISC1 and directly measurable trait variables such as working memory, cognitive aging, and decreased gray matter volume in the prefrontal cortex, abnormalities in hippocampal structure and function, and reduction in the amplitude of the P300 event-related potential. Further, DISC1 binds a number of proteins known to be involved in essential processes of neuronal function, including neuronal migration, neurite outgrowth, cytoskeletal modulation, and signal transduction. Thus, both genetic and functional data provide evidence for a critical role for DISC1 in schizophrenia and related disorders, supporting the neurodevelopmental hypothesis for the molecular pathogenesis of these devastating illnesses.     

Interactions of human truncated DISC1 proteins: implications for schizophrenia

Numerous genetic linkage and association reports have implicated the Disrupted-in-Schizophrenia (DISC1) gene in psychiatric illness. The Scottish family translocation, predicted to encode a C-terminus-truncated protein, suggests involvement of short isoforms in the pathophysiology of mental disorders. We recently reported complex alternative splicing patterns for the DISC1 gene and found that short isoforms are overexpressed in the brains of patients with schizophrenia and in carriers of risk-associated alleles. Investigation into the protein–protein interactions of alternative DISC1 isoforms may provide information about the functional consequences of overexpression of truncated forms in mental illness. Human embryonic kidney (HEK293) cells were transiently co-transfected with human epitope-tagged DISC1 variants and epitope-tagged NDEL1, FEZ1, GSK3β and PDE4B constructs. Co-immunoprecipitation assays demonstrated that all truncated DISC1 variants formed complexes with full-length DISC1. Short DISC1 splice variants LΔ78, LΔ3 and Esv1 showed reduced or no binding to NDEL1 and PDE4B proteins, but fully interacted with FEZ1 and GSK3β. The temporal expression pattern of GSK3β in the human postmortem tissue across the lifespan closely resembled that of the truncated DISC1 variants, suggesting the possibility of interactions between these proteins in the human brain. Our results suggest that complexes of full-length DISC1 with truncated DISC1 variants may result in cellular disturbances critical to DISC1 function.     

Genetic and pharmacological evidence for schizophrenia‐related Disc1 interaction with GSK‐3

Recent studies have identified disrupted‐in‐schizophrenia‐1 (DISC1) as a strong genetic risk factor associated with schizophrenia. Previously, we have reported that a mutation in the second exon of the DISC1 gene [leucine to proline at amino acid position 100, L100P] leads to the development of schizophrenia‐related behaviors in mice. Glycogen synthase kinase‐3 (GSK‐3) is a serine/threonine protein kinase that interacts with the N‐terminal region of DISC1 (aa 1–220) and has been implicated as an important downstream component in the etiology of schizophrenia. Here, for the first time, we show that pharmacological and genetic inactivation of GSK‐3 reverse prepulse inhibition and latent inhibition deficits as well as normalizing the hyperactivity of Disc1‐L100P mutants. In parallel to these observations, interaction between DISC1 and GSK‐3α and β is reduced in Disc1‐L100P mutants. Our data provide genetic, biochemical, and behavioral evidence for a molecular link between DISC1 and GSK‐3 in relation to psychopathology and highlights the value of missense mutations in dissecting the underlying and complex molecular mechanisms of neurological disorders. Synapse, 2010. © 2010 Wiley‐Liss, Inc.     

Disruption of exploratory and habituation behavior in mice with mutation of DISC1: an ethologically based analysis

Disrupted-in-schizophrenia-1 (DISC1) is a gene that has been functionally linked with neurodevelopmental processes and structural plasticity in the brain. Clinical genetic investigations have implicated DISC1 as a genetic risk factor for schizophrenia and related psychoses. Studies using mutant mouse models of DISC1 gene function have demonstrated schizophrenia-related anatomical and behavioral endophenotypes. In the present study, ethologically based assessment of exploratory and habituation behavior in the open field was conducted in DISC1 (L100P), wild-type (WT), heterozygous (HET), and homozygous (HOM) mutant mice of both sexes. Ethological assessment was conducted in an open-field environment to explore specific topographies of murine exploratory behavior across the extended course of interaction from initial exploration through subsequent habituation (the ethogram). During initial exploration, HET and HOM DISC1 mutants evidenced increased levels of locomotion and rearing to wall compared with WT. A HOM-specific increase in total rearing and a HET-specific increase in sifting behavior and reduction in rearing seated were also observed. Over subsequent habituation, locomotion, sniffing, total rearing, rearing to wall, rearing free, and rearing seated were increased in HET and HOM mutants vs. WT. Overall, grooming was increased in HOM relative to other genotypes. HET mice displayed a selective decrease in habituation of sifting behavior. These data demonstrate impairment in both initial exploratory and habituation of exploration in a novel environment in mice with mutation of DISC1. This is discussed in the context of the functional role of the gene vis à vis a schizophrenia phenotype as well as the value of ethologically based approaches to behavioral phenotyping.     

A haplotype within the DISC1 gene is associated with visual memory functions in families with a high density of schizophrenia

We have previously reported evidence of linkage and association between markers on 1q42 and schizophrenia in a study sample of 498 multiply affected Finnish nuclear families, leading to the recent identification of four significantly associated haplotypes that specifically implicate the Translin-Associated Factor X (TRAX) and Disrupted in Schizophrenia 1 and 2 (DISC1 and DISC2) genes in the genetic etiology of schizophrenia. Previously, the DISC genes were found to be disrupted by a balanced translocation (1;11)(q42.1;q14.3) that cosegregated with schizophrenia and related disorders in a large Scottish pedigree. Interestingly, we also reported earlier suggestive linkage between endophenotypic quantitative traits of visual and verbal memory and microsatellite markers in close proximity to TRAX/DISC, on 1q41. Here, we tested if the identified allelic haplotypes of TRAX/DISC would be associated with visual and/or verbal memory function impairments that are known to aggregate with schizophrenia in families. One haplotype of DISC1, HEP3, displayed association with poorer performance on tests assessing short-term visual memory and attention. Analysis of affected and unaffected offspring separately revealed that both samples contribute to the observed association to visual working memory. These results provide genetic support to the view that the DISC1 gene contributes to sensitivity to schizophrenia and associated disturbances and affects short-term visual memory functions. This finding should stimulate studies aiming at the molecular characterization of how the specific alleles of DISC1 affect the visual memory functions and eventually participates in the development of schizophrenia.     

Disrupted-in-Schizophrenia-1 SNPs and Susceptibility to Schizophrenia: Evidence from Malaysia

Objective

Even though the role of the DICS1 gene as a risk factor for schizophrenia is still unclear, there is substantial evidence from functional and cell biology studies that supports the connection of the gene with schizophrenia. The studies associating the DISC1 gene with schizophrenia in Asian populations are limited to East-Asian populations. Our study examined several DISC1 markers of schizophrenia that were identified in the Caucasian and East-Asian populations in Malaysia and assessed the role of rs2509382, which is located at 11q14.3, the mutual translocation region of the famous DISC1 translocation [t (1; 11) (p42.1; q14.3)].

Methods

We genotyped eleven single-neucleotide polymorphism (SNPs) within or related to DISC1 (rs821597, rs821616, rs4658971, rs1538979, rs843979, rs2812385, rs1407599, rs4658890, and rs2509382) using the PCR-RFLP methods.

Results

In all, there were 575 participants (225 schizophrenic patients and 350 healthy controls) of either Malay or Chinese ethnicity. The case-control analyses found two SNPs that were associated with schizophrenia [rs4658971 (p=0.030; OR=1.43 (1.35-1.99) and rs1538979-(p=0.036; OR=1.35 (1.02-1.80)] and rs2509382-susceptibility among the males schizophrenics [p=0.0082; OR=2.16 (1.22-3.81)]. This is similar to the meta-analysis findings for the Caucasian populations.

Conclusion

The study supports the notion that the DISC1 gene is a marker of schizophrenia susceptibility and that rs2509382 in the mutual DISC1 translocation region is a susceptibility marker for schizophrenia among males in Malaysia. However, the finding of the study is limited due to possible genetic stratification and the small sample size.     

Association of DISC1 with autism and Asperger syndrome

The DISC1 gene at 1q42 has generated considerable interest in various psychiatric diseases, since a balanced translocation interrupting the gene was found to cosegregate with schizophrenia and related mental illnesses in a large Scottish pedigree. To date, linkage and association findings to this locus have been replicated in several study samples ascertained for psychotic disorders. However, the biological function of DISC1 in neuronal development would suggest a potential role for this gene also in other, early onset neuropsychiatric disorders. Here we have addressed the allelic diversity of the DISC1, DISC2 and TRAX genes, clustered in 1q42, in Finnish families ascertained for infantile autism (97 families, n(affected)=138) and Asperger syndrome (29 families, n(affected)=143). We established association between autism and a DISC1 intragenic microsatellite (D1S2709; P=0.004). In addition, evidence for association to Asperger syndrome was observed with an intragenic single nucleotide polymorphism (SNP) of DISC1 (rs1322784; P=0.0058), as well as with a three-SNP haplotype (P=0.0013) overlapping the HEP3 haplotype, that was previously observed to associate with schizophrenia in Finnish families. The strongest associations were obtained with broad diagnostic categories for both disorders and with affected males only, in agreement with the previous sex-dependent effects reported for DISC1. These results would further support the involvement of DISC1 gene also in the etiopathogenesis of early onset neuropsychiatric disorders.     

Disrupted in schizophrenia 1 genotype and positive symptoms in schizophrenia.

BACKGROUND: Converging evidence has demonstrated an association between the Disrupted in Schizophrenia 1 (DISC1) gene and schizophrenia (SZ). Within the DISC1 gene, a single nucleotide polymorphism (SNP), Ser704Cys, has been associated with the structure and function of the hippocampus. Because positive symptoms in SZ have also been associated with hippocampal structure and function, we hypothesized that variation in a DISC1 haplotype containing Ser704Cys would be significantly associated with positive symptomatology in SZ. METHODS: We tested for an association between variation in a haplotype block within the DISC1 gene containing Ser704Cys and lifetime history of positive symptoms in 199 Caucasian patients with SZ. RESULTS: We detected significant associations between a DISC1 haplotype containing Ser704Cys and Ser704Cys genotype and lifetime severity of delusions in SZ. CONCLUSIONS: These data suggest that that the effect of DISC1 genetic variation might be associated with positive symptoms in patients with SZ.     

Possible association between Interleukin-1beta gene and schizophrenia in a Japanese population

Background

Disrupted-in-Schizophrenia 1 (DISC1) gene is one of the most promising candidate genes for major mental disorders. In a previous study, a Finnish group demonstrated that DISC1 polymorphisms were associated with autism and Asperger syndrome. However, the results were not replicated in Korean population. To determine whether DISC1 is associated with autism in Chinese Han population, we performed a family-based association study between DISC1 polymorphisms and autism.

Methods

We genotyped seven tag single nucleotide polymorphisms (SNPs) in DISC1, spanning 338 kb, in 367 autism trios (singleton and their biological parents) including 1,101 individuals. Single SNP association and haplotype association analysis were performed using the family-based association test (FBAT) and Haploview software.

Results

We found three SNPs showed significant associations with autism (rs4366301: G > C, Z = 2.872, p = 0.004; rs11585959: T > C, Z = 2.199, p = 0.028; rs6668845: A > G, Z = 2.326, p = 0.02). After the Bonferroni correction, SNP rs4366301, which located in the first intron of DISC1, remained significant. When haplotype were constructed with two-markers, three haplotypes displayed significant association with autism. These results were still significant after using the permutation method to obtain empirical p values.

Conclusions

Our study provided evidence that the DISC1 may be the susceptibility gene of autism. It suggested DISC1 might play a role in the pathogenesis of autism.     

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.     

Subcellular targeting of DISC1 is dependent on a domain independent from the Nudel binding site

Disrupted in schizophrenia 1 (DISC1) has been identified as a putative risk factor for schizophrenia and affective disorders through study of a Scottish family with a balanced (1;11) (q42.1;q14.3) translocation, which results in the disruption of the DISC1 locus and cosegregates with major psychiatric disease. Several other reports of genetic linkage and association between DISC1 and schizophrenia in a range of patient populations have added credibility to the DISC1-schizophrenia theory, but the function of the DISC1 protein is still poorly understood. Recent studies have suggested that DISC1 plays a role in neuronal outgrowth, possibly through reported interactions with the molecules Nudel and FEZ1. Here we have analyzed the DISC1 protein sequence to identify previously unknown regions that are important for the correct targeting of the protein and conducted imaging studies to identify DISC1 subcellular location. We have identified a central coiled-coil region and show it is critical for the subcellular targeting of DISC1. This domain is independent from the C-terminal Nudel binding domain highlighting the multidomain nature/functionality of the DISC1 protein. Furthermore, we have been able to provide the first direct evidence that DISC1 is localized to mitochondria in cultured cortical neurons that are dependent on an intact cytoskeleton. Surprisingly, Nudel is seen to differentially associate with mitochondrial markers in comparison to DISC1. Disruption of the cytoskeleton results in colocalization of Nudel and mitochondrial markers-the first observation of such a direct relationship. Mitochondrial dysfunction has been implicated to play a role in schizophrenia so we speculate that mutations in DISC1 or Nudel may impair mitochondrial transport or function, initiating a cascade of events culminating in psychiatric illness.     

Functional genomics in postmortem human brain: abnormalities in a DISC1 molecular pathway in schizophrenia

The disrupted in schizophrenia 1 (DISC1) gene has been identified as a schizophrenia susceptibility gene based on linkage and single nucleotide polymorphism (SNP) association studies and clinical data, suggesting that risk SNPs impact on hippocampal structure and function. We hypothesized that altered expression of DISC1 and/or its molecular partners (nuclear distribution element-like [NUDEL], fasciculation and elongation protein zeta-i [FEZ1], and lissencephaly 1 [LIS1]) may underlie its pathogenic role in schizophrenia and explain its genetic association. We examined the expression of DISC1 and its binding partners in the hippocampus and dorsolateral prefrontal cortex of postmortem human brains of schizophrenic patients and controls. We found no difference in the expression of DISC1 mRNA in schizophrenia, and no association with previously identified risk SNPs. However, the expression of NUDEL, FEZ1, and LIS1 was significantly reduced in tissue from schizophrenic subjects, and the expression of each showed association with high-risk DISC1 polymorphisms. These data suggest involvement of genetically linked abnormalities in the DISC1 molecular pathway in the pathophysiology of schizophrenia.