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

Disrupted-in-Schizophrenia-1

Chromosomal abnormalities can be powerful tools to identify genes that influence disease risk. The study of a chromosome translocation that segregated with severe psychiatric illness in a large family led directly to the discovery of a gene disrupted by a chromosomal breakpoint. Disrupted-in-Schizophrenia-1 (DISC1) is now an important candidate risk gene for schizophrenia and affective disorders. We review the work that led up to this discovery and the evidence that it is important in the wider population with schizophrenia and affective disorders. We also discuss the latest findings on the neuronal functions of the protein DISC1 encoded by the gene.

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.

Association study of brain-derived neurotrophic factor and apolipoprotein E polymorphisms and cognitive function in aged males without dementia

Genetic factors for inter-individual variation in cognition have been arousing great interest among researchers. Among the many associated genes, brain-derived neurotrophic factor (BDNF) and apolipoprotein E (APOE), as two of the most frequently studied, might be good prospects for cognitive genetics. Thus, the aim of this study was to investigate both the isolated and cooperative effect of BDNF and APOE on normal cognitive ageing. A homogeneous population of Chinese aged males (N=161) were genotyped for functional genetic variants of BDNF (BDNF-G196A) and APOE (APOE-epsilon4) and assessed by a comprehensive neuropsychological measurement (Cognitive Abilities Screening Instrument Chinese version; CASI C-2.0). Thereafter genotypic group differences of BDNF and APOE in CASI cognitive profiles were tested. Results from the present study suggest the possible influence of APOE on specific cognitive domains (CASI orientation and language domains; p=0.010 and 0.028, respectively), whereas there was no significant role of BDNF, either solely or with APOE, in cognition in the elderly. Our findings suggest a possible association between APOE-epsilon4 and specific cognitive domains in the aged male, whereas the functional genetic variant of BDNF (BDNF-G196A) played no significant role in normal cognitive ageing.

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.

The Lothian Birth Cohort 1936: a study to examine influences on cognitive ageing from age 11 to age 70 and beyond

BACKGROUND

Cognitive ageing is a major burden for society and a major influence in lowering people's independence and quality of life. It is the most feared aspect of ageing. There are large individual differences in age-related cognitive changes. Seeking the determinants of cognitive ageing is a research priority. A limitation of many studies is the lack of a sufficiently long period between cognitive assessments to examine determinants. Here, the aim is to examine influences on cognitive ageing between childhood and old age.

METHODS/DESIGN

The study is designed as a follow-up cohort study. The participants comprise surviving members of the Scottish Mental Survey of 1947 (SMS1947; N = 70,805) who reside in the Edinburgh area (Lothian) of Scotland. The SMS1947 applied a valid test of general intelligence to all children born in 1936 and attending Scottish schools in June 1947. A total of 1091 participants make up the Lothian Birth Cohort 1936. They undertook: a medical interview and examination; physical fitness testing; extensive cognitive testing (reasoning, memory, speed of information processing, and executive function); personality, quality of life and other psycho-social questionnaires; and a food frequency questionnaire. They have taken the same mental ability test (the Moray House Test No. 12) at age 11 and age 70. They provided blood samples for DNA extraction and testing and other biomarker analyses. Here we describe the background and aims of the study, the recruitment procedures and details of numbers tested, and the details of all examinations.

DISCUSSION

The principal strength of this cohort is the rarely captured phenotype of lifetime cognitive change. There is additional rich information to examine the determinants of individual differences in this lifetime cognitive change. This protocol report is important in alerting other researchers to the data available in the cohort.

Functional genomics and schizophrenia: endophenotypes and mutant models

This article summarizes the rationale, methods, and results of gene discovery programs in schizophrenia research and describes functional methods of investigating potential candidate genes. It focuses next on the most prominent current candidate genes and describes (1) evidence for their association with schizophrenia and research into the function of each gene; (2) investigation of the clinical phenotypes and endophenotypes associated with each gene, at the levels of psychopathologic, neurocognitive, electrophysiologic, neuroimaging, and neuropathologic findings; and (3) research into the ethologic, cognitive, social, and psychopharmacologic phenotype of mutants with targeted deletion of each gene. It examines gene-gene and gene-environment interactions. Finally, it looks at future directions for research.

Update on psychiatric genetics

Genetic factors play a fundamental role in the genesis of many mental disorders. The identification of the underlying genetic variation will therefore transform parts of psychiatry toward a neuroscience-based discipline. With the sequence of the human genome now available, the majority of common variations identified, and new high-throughput technologies arriving in academic research laboratories, the identification of genes is expected to explain a large proportion of the risk of developing mental disorders. So far, a number of risk genes have been identified, but no major gene has emerged. The majority of these genes participate in the regulation of biogenic amines that play critical roles in affect modulation and reward systems. The identification of genetic variations associated with mental disorders should provide an approach to evaluate risk for mental disorders, adjust pharmacotherapy on the individual level, and even allow for preventive interactions. New targets for the development of treatment are anticipated to derive from results of genetic studies. In this review, we summarize the current state of psychiatric genetics, underscore current discussions, and predict where the field is expected to move in the near future.

Association of distinct allelic haplotypes of DISC1 with psychotic and bipolar spectrum disorders and with underlying cognitive impairments

Bipolar disorder (BPD) and schizophrenia (SCZ) have at least a partially convergent aetiology and thus may share genetic susceptibility loci. Multiple lines of evidence emphasize the role of disrupted-in-schizophrenia-1 (DISC1) gene in psychotic disorders such as SCZ. We monitored the association of allelic variants of translin-associated factor X (TSNAX)/DISC1 gene cluster using 13 single-nucleotide polymorphisms (SNPs) in 723 members of 179 Finnish BPD families. Consistent with an earlier finding in Finnish SCZ families, the haplotype T-A of rs751229 and rs3738401 at the 5' end of DISC1 was over-transmitted to males with psychotic disorder (P = 0.008; for an extended haplotype P = 0.0007 with both genders). Haplotypes at the 3' end of DISC1 associated with bipolar spectrum disorder (P = 0.0002 for an under-transmitted haplotype T-T of rs821616 and rs1411771, for an extended haplotype P = 0.0001), as did a two-SNP risk haplotype at the 5' end of TSNAX (P = 0.007). The risk haplotype for psychotic disorder also associated to perseverations (P = 0.035; for rs751229 alone P = 0.0012), and a protective haplotype G-T-G with rs1655285 in addition to auditory attention (P = 0.0059). The 3' end variants associated with several cognitive traits, with the most robust signal for rs821616 and verbal fluency and rs980989 and psychomotor processing speed (P = 0.011 for both). These results support involvement of DISC1 in the genetic aetiology of BPD and suggest that its distinct variants contribute to variation in the dimensional features of psychotic and bipolar spectrum disorders. Finding of alternative associating haplotypes in the same set of BPD families gives evidence for allelic heterogeneity within DISC1, eventually leading to heterogeneity in the clinical outcome as well.

Hippocampal CA1 pyramidal cell size is reduced in bipolar disorder

1. Schizophrenia and bipolar disorder are neurodevelopmental disorders with significant genetic vulnerabilities. Several trophic genes and/or proteins have been implicated in the causation for both disorders.2. We hypothesized that these genes and/or proteins may impact neuronal growth in both disorders.3. Hippocampal tissue sections from CA1 area of schizophrenic, bipolar, depressed, and controls subjects, matched for age, sex, PMI, drug exposure, and brain pH were prepared for cell size determination using the Stanley Medical Research Foundation postmortem brain collection.4. Quantification of hippocampal CA1 pyramidal neuron size showed a significant 12% reduction in cell size (p < 0.05) in bipolar subjects vs. controls. There were nonsignificant trends for reduction in cell size in both schizophrenic and depressed subjects vs. controls.5. These results indicate for the first time that pyramidal cell atrophy is present in hippocampus of subjects with bipolar disorder.

Positive association of the Disrupted-in-Schizophrenia-1 gene (DISC1) with schizophrenia in the Chinese Han population

Disrupted-in-Schizophrenia-1 (DISC1) is located on 1q42.1, one of the most promising susceptibility loci in schizophrenia linkage studies. A non-synonymous genetic variation rs821616 (Ser704Cys) in DISC1, has recently been shown to be associated with schizophrenia in family-based study [Callicott et al. (2005); Proc Natl Acad Sci USA 102: 8627-8632]. In order to further confirm this issue, we examined four single nucleotide polymorphisms (SNPs) in a chromosomal region spanning 42 kb of this gene, namely rs821616, rs821597, rs4658971, and rs843979, in Chinese sample of 313 schizophrenia patients and 317 healthy controls. Our results showed that two SNPs had strong associations with schizophrenia (rs821616: Allele A > T, chi(2) = 7.8006, df = 1, P = 0.0052; Genotype, chi(2) = 7.7935, df = 2, P = 0.0203; rs821597: Allele A > G, chi(2) = 9.5404, df = 1, P = 0.0020; Genotype, chi(2) = 12.2780, df = 2, P = 0.0022). When haplotypes were constructed with two, three, and four markers, a number of haplotype combinations, especially those including rs821616 and rs821597, were significantly associated with schizophrenia. Furthermore, there was a strong evidence for association in a four-marker haplotype analysis (chi(2) = 7.686, df = 4, P = 0.005581, corrected P = 0.006199). Although the case-control and family-based association studies both suggest that DISC1 gene may play a role in genetic susceptibility to schizophrenia, the risk haplotypic combinations have subtle differences in the two studies. Our findings provide further evidence for DISC1 as a predisposing gene involved in schizophrenia in the Chinese Han Population.

Role of DISC1 in neural development and schizophrenia

How can we hope to explain mechanistically the schizophrenic phenotype? Perhaps through the reductionist approach of genetics, which is beginning to yield biological clues. Growing evidence supports the view that the well-established genetic risk factor DISC1 plays an important role in schizophrenia biology by interacting with FEZ1 and NDEL1 during neurodevelopment and with the phosphodiesterase PDE4B in neuronal cell signalling. Thus, DISC1 and its pathways support the neurodevelopmental hypothesis of schizophrenia and provide a mechanistic explanation for the characteristic cognitive deficits. Genetic variants of DISC1 also predispose to related affective (mood) disorders. As a consequence, we can speculate on the mechanisms of DISC1 action and possible routes to treatment for these common, debilitating brain disorders.

Disrupted in Schizophrenia 1 Interactome: evidence for the close connectivity of risk genes and a potential synaptic basis for schizophrenia

Disrupted in Schizophrenia 1 (DISC1) is a schizophrenia risk gene associated with cognitive deficits in both schizophrenics and the normal ageing population. In this study, we have generated a network of protein-protein interactions (PPIs) around DISC1. This has been achieved by utilising iterative yeast-two hybrid (Y2H) screens, combined with detailed pathway and functional analysis. This so-called 'DISC1 interactome' contains many novel PPIs and provides a molecular framework to explore the function of DISC1. The network implicates DISC1 in processes of cytoskeletal stability and organisation, intracellular transport and cell-cycle/division. In particular, DISC1 looks to have a PPI profile consistent with that of an essential synaptic protein, which fits well with the underlying molecular pathology observed at the synaptic level and the cognitive deficits seen behaviourally in schizophrenics. Utilising a similar approach with dysbindin (DTNBP1), a second schizophrenia risk gene, we show that dysbindin and DISC1 share common PPIs suggesting they may affect common biological processes and that the function of schizophrenia risk genes may converge.

Are some genetic risk factors common to schizophrenia, bipolar disorder and depression? Evidence from DISC1, GRIK4 and NRG1

Depression is common in patients with schizophrenia and it is well established from family studies that rates of depression are increased among relatives of probands with schizophrenia, making it likely that the phenotypes described under the categories of affective and non-affective psychoses share some genetic risk factors. Family linkage studies have identified several chromosomal regions likely to contain risk genes for schizophrenia and bipolar disorder, suggesting common susceptibility loci. Candidate gene association studies have provided further evidence to suggest that some genes including two of the most studied candidates, Disrupted in Schizophrenia 1 (DISC1) and Neuregulin 1 (NRG1) may be involved in both types of psychosis. We have recently identified another strong candidate for a role in both schizophrenia and affective disorders, GRIK4 a glutamate receptor mapped to chromosome 11q23 [Glutamate Receptor, Ionotropic, Kainate, type 4]. This gene is disrupted by a translocation breakpoint in a patient with schizophrenia, and case control studies show significant association of GRIK4 with both schizophrenia and bipolar disorder. Identifying genes implicated in the psychoses may eventually provide the basis for classification based on biology rather than symptoms, and suggest novel treatment strategies for these complex brain disorders.

Schizophrenia in translation: disrupted in schizophrenia (DISC1): integrating clinical and basic findings

The disrupted in schizophrenia 1 (DISC1) gene has been linked to schizophrenia and other serious mental illnesses in multiple pedigrees. This article will review the neurobiology of DISC1 in normal developing and adult brain and the putative role of the mutant form in major mental illness, particularly schizophrenia. The initial genetic finding of an association between DISC1 and schizophrenia in a Scottish population has now been replicated in Finnish, American, Japanese, and Taiwanese populations. DISC1 is present throughout the brain of a variety of species during development and adulthood, including many of the brain regions known to be abnormal in schizophrenia, such as the prefrontal cortex, hippocampus, and thalamus. The functions of DISC1 in the developing brain include neuronal migration, neurite outgrowth, and neurite extension. In the adult, DISC1 has been identified in multiple populations of neurons and in structures associated with synaptic function, suggesting that one of its adult functions may be synaptic plasticity. DISC1 is associated with numerous cognitive functions that are abnormal in schizophrenia. Converging evidence from cell culture, mice mutants, postmortem brain, and genetics implicates mutant DISC1 in the pathophysiology of schizophrenia and other mental illnesses.

Families with the risk allele of DISC1 reveal a link between schizophrenia and another component of the same molecular pathway, NDE1

We have previously reported a robust association between an allelic haplotype of 'Disrupted in Schizophrenia 1' (DISC1) and schizophrenia in a nationwide collection of Finnish schizophrenia families. This specific DISC1 allele was later identified to associate with visual working memory, selectively in males. DISC1 association to schizophrenia has since been replicated in multiple independent study samples from different populations. In this study, we conditioned our sample of Finnish families for the presence of the Finnish tentative risk allele for DISC1 and re-analyzed our genome-wide scan data of 443 markers on the basis of this stratification. Two additional loci displayed an evidence of linkage (LOD > 3) and included a locus on 16p13, proximal to the gene encoding NDE1, which has been shown to biologically interact with DISC1. Although none of the observed linkages remained significant after multiple test correction through simulation, further analysis of NDE1 revealed an association between a tag-haplotype and schizophrenia (P = 0.00046) specific to females, which proved to be significant (P = 0.011) after multiple test correction. Our finding would support the concept that initial gene findings in multifactorial diseases will assist in the identification of other components of complex genetic etiology. Notably, this and other converging lines of evidence underline the importance of DISC1-related functional pathways in the etiology of schizophrenia.

DISC1–NDEL1/NUDEL protein interaction, an essential component for neurite outgrowth, is modulated by genetic variations of DISC1

Disrupted-In-Schizophrenia-1 (DISC1) is a unique susceptibility gene for major mental conditions, because of the segregation of its genetic variant with hereditary psychosis in a Scottish pedigree. Genetic association studies reproducibly suggest involvement of DISC1 in both schizophrenia and bipolar disorder in several ethnic groups. The DISC1 protein is multifunctional, and a pool of DISC1 in the dynein motor complex is required for neurite outgrowth in PC12 cells as well as proper neuronal migration and dendritic arborization in the developing cerebral cortex in vivo. Here, we show that a specific interaction between DISC1 and nuclear distribution element-like (NDEL1/NUDEL) is required for neurite outgrowth in differentiating PC12 cells. Among several components of the dynein motor complex, DISC1 and NDEL1 are selectively upregulated during neurite outgrowth upon differentiation in PC12 cells. The NDEL1 binding site of DISC1 was narrowed down to a small portion of exon 13, corresponding to amino acids 802-835 of DISC1. We demonstrate that genetic variants of DISC1, proximal to the NDEL1 binding site, affect the interaction between DISC1 and NDEL1.

Primate disrupted-in-schizophrenia-1 (DISC1): high divergence of a gene for major mental illnesses in recent evolutionary history

Here we analyze the species conservation of disrupted-in-schizophrenia-1 (DISC1) gene, a susceptibility gene for schizophrenia. We cloned cDNA of DISC1 and characterized DISC1 protein in monkey brains and compared their features with those in a variety of species, including humans, rodents and lower vertebrates. Sequences of human and monkey DISC1 are very similar for both nucleotides and amino acids, in sharp contrast to those of rodents; this is reminiscent of G72, another gene involved in major mental illnesses. Bioinformatic cross-species comparisons identified a portion of DISC1 sequences in chicken and Caenorhabditis elegans, but failed to find DISC1 in Drosophila. In contrast to sequence differences, the regional expression profile of DISC1 is well conserved between rodents and primates in that levels of DISC1 mRNA and protein are higher in the hippocampus and the cerebral cortex, and much lower in cerebellum in adult brains. The findings of this study may suggest overall patterns of evolution of genes for psychiatric disorders, and thus assist in production of genetically-engineered mice, and the interpretation of the underlying mechanisms of psychiatric conditions.

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.

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.

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.

Chromosomal abnormalities and psychosis

The search for susceptibility genes for schizophrenia and severe affective disorder has been enhanced by the study of cytogenetic abnormalities that disrupt genes directly. One such gene is DISCI and there is increasing evidence that it may be an important modulator of risk of psychosis.

Disrupted in schizophrenia 1: building brains and memories

Schizophrenia and bipolar affective disorder are common, debilitating, and poorly understood and treated disorders. Both conditions are highly heritable. Recent genetic studies have suggested that the gene disrupted in schizophrenia 1 (DISC1) is an important risk factor. DISC1 seems to have a key role in building the brain and memories by interacting with other proteins, including nuclear distribution E-like protein and phosphodiesterase 4B. Here, we review the current knowledge, highlight some key unanswered questions and propose ways forward towards a better understanding of normal and abnormal brain development and function. In the long term, this might lead to the discovery of drugs that are more efficacious and safer than currently available ones.

The brain-derived neurotrophic factor Val66Met polymorphism is associated with age-related change in reasoning skills

A polymorphism (Val66Met) in the gene encoding brain-derived neurotrophic factor (BDNF) has previously been associated with impaired hippocampal function and scores on the Logical Memory subtest of the Wechsler Memory Scale-Revised (WMS-R). Despite its widespread expression in the brain, there have been few studies examining the role of BDNF on cognitive domains, other than memory. We examined the association between BDNF Val66Met genotype and non-verbal reasoning, as measured by Raven's standard progressive matrices (Raven), in two cohorts of relatively healthy older people, one aged 79 (LBC1921) and the other aged 64 (ABC1936) years. LBC1921 and ABC1936 subjects had reasoning measured at age 11 years, using the Moray House Test (MHT), in the Scottish Mental Surveys of 1932 and 1947, respectively. BDNF genotype was significantly associated with later life Raven scores, controlling for sex, age 11 MHT score and cohort (P = 0.001). MHT, Verbal Fluency and Logical Memory scores were available, in later life, for LBC1921 only. BDNF genotype was significantly associated with age 79 MHT score, controlling for sex and age 11 MHT score (P = 0.016). In both significant associations, Met homozygotes scored significantly higher than heterozygotes and Val homozygotes. This study indicates that BDNF genotype contributes to age-related changes in reasoning skills, which are closely related to general intelligence.

Expression of DISC1 binding partners is reduced in schizophrenia and associated with DISC1 SNPs

DISC1 has been identified as a schizophrenia susceptibility gene based on linkage and SNP association studies and clinical data suggesting that risk SNPs impact on hippocampal structure and function. In cell and animal models, C-terminus-truncated DISC1 disrupts intracellular transport, neural architecture and migration, perhaps because it fails to interact with binding partners involved in neuronal differentiation such as fasciculation and elongation protein zeta-1 (FEZ1), platelet-activating factor acetylhydrolase, isoform Ib, PAFAH1B1 or lissencephaly 1 protein (LIS1) and nuclear distribution element-like (NUDEL). We hypothesized that altered expression of DISC1 and/or its molecular partners may underlie its pathogenic role in schizophrenia and explain its genetic association. We examined the expression of DISC1 and these selected binding partners as well as reelin, a protein in a related signaling pathway, in the hippocampus and dorsolateral prefrontal cortex of postmortem human brain patients with schizophrenia and controls. We found no difference in the expression of DISC1 or reelin mRNA in schizophrenia and no association with previously identified risk DISC1 SNPs. However, the expression of NUDEL, FEZ1 and LIS1 was each significantly reduced in the brain tissue from patients with schizophrenia and expression of each showed association with high-risk DISC1 polymorphisms. Although, many other DISC1 binding partners still need to be investigated, these data implicate genetically linked abnormalities in the DISC1 molecular pathway in the pathophysiology of schizophrenia.

Genetic variation in DTNBP1 influences general cognitive ability

Human intelligence is a trait that is known to be significantly influenced by genetic factors, and recent linkage data provide positional evidence to suggest that a region on chromosome 6p, previously associated with schizophrenia, may be linked to variation in intelligence. The gene for dysbindin-1 (DTNBP1) is located at 6p and has also been implicated in schizophrenia, a neuropsychiatric disorder characterized by cognitive dysfunction. We report an association between DTNBP1 genotype and general cognitive ability (g) in two independent cohorts, including 213 patients with schizophrenia or schizo-affective disorder and 126 healthy volunteers. These data suggest that DTNBP1 genetic variation influences human intelligence.

DISC1 immunoreactivity at the light and ultrastructural level in the human neocortex

Disrupted-In-Schizophrenia 1 (DISC1) is one of two genes that straddle the chromosome 1 breakpoint of a translocation associated with an increased risk of schizophrenia. DISC1 has been identified in the brain of various mammalian species, but no previous immunocytochemical studies have been conducted in human neocortex. We examined DISC1 immunoreactivity in frontal and parietal cortex (BA 4, 9, 39, and 46) in normal human brain. At the light microscopic level, immunolabeling was prominent in the neuropil, in multiple populations of cells, and in the white matter. At the ultrastructural level, staining was prominent in structures associated with synaptic function. Immunolabeled axon terminals comprised 8% of all terminals and formed both asymmetric and symmetric synapses. Labeled axon terminals formed synapses with labeled spines and dendrites; in some, only the postsynaptic density (PSD) of the postsynaptic structure was labeled. The most common configuration, however, was an unlabeled axon terminal forming an asymmetric synapse with a spine that had immunoreactivity deposited on the PSD and throughout the spine. The presence of DISC1 in multiple types of synapses suggests the involvement of DISC1 in corticocortical as well as thalamocortical connections. Staining was also present in ribosomes, parts of the chromatin, in dendritic shafts, and on some microtubules. Labeling was absent from the Golgi apparatus and multivesicular bodies, which are associated with protein excretion. These anatomical localization data suggest that DISC1 participates in synaptic activity and microtubule function, and are consistent with the limited data on its adult function.