Chromosome 1 loci in Finnish schizophrenia families

Carving chaos: genetics and the classification of mood and psychotic syndromes

Though Kraepelin's century-old division of major mental illness into mood disorder and schizophrenia remains in place, debate abounds over the most appropriate classification. Although these arguments previously rested solely on clinical grounds, they now are rooted in genetics and neurobiology. This article reviews evidence from the fields of genetic epidemiology, linkage, association, cytogenetics, and gene expression. Taken together, these data suggest some overlap in the genes that predispose to bipolar disorder and schizophrenia. One gene, DAOA (D-amino acid oxidase activator, also known as G72), has been repeatedly implicated as an overlap gene, while DISC1 and others may constitute additional shared susceptibility genes. Further, some evidence implicates syndromes of co-occurring mood and psychotic symptoms in association with the putative risk alleles in overlap genes. From a nosologic perspective, the existence of overlap genes, coupled with the genotype-phenotype correlations discovered to date, supports the reality of the much debated schizoaffective disorder. Potential non-overlap syndromes--such as nonpsychotic bipolar disorder or cyclothymic temperament, on the one hand, and negative symptoms or the deficit syndrome, on the other--could turn out to have their own unique genetic determinants. If genotypes are to be the anchor points of a clinically useful system of classification, they must ultimately be shown to inform prognosis, treatment, and prevention. No gene variants have yet met these tests in bipolar disorder or schizophrenia.

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.

Affective flattening and alogia associate with the familial form of schizophrenia

Family history of schizophrenia has been associated with negative symptoms in the clinical picture. Our aim was to examine the signs and symptoms of schizophrenia in a genetically homogeneous isolate and a nationwide multiplex family sample, and to investigate the symptom dimensions and their association with the degree of familial loading for psychotic disorders and with consanguinity. For factor analysis of the Scales for the Assessment of Negative and Positive Symptoms, we included 290 patients with a DSM-IV diagnosis of schizophrenia: 63 multiplex family and 133 singleton patients from the isolate, and 94 nationwide multiplex family patients. The factor analysis yielded four factors. There was a significant difference between the multiplex and singleton patients, the former having more severe affective flattening and alogia. Further, the patients in isolate groups had fewer delusions and hallucinations compared with the whole country multiplex patients regardless of their familial loading for schizophrenia. This may be related to genetic homogeneity in the isolate. We conclude that patients with first-degree relatives with psychotic disorder have more severe negative symptoms.

Schizophrenia genetics: uncovering positional candidate genes

The efforts to decipher the genetic causes of schizophrenia, one of the most devastating mental illnesses, have reached a turning point. Several linkage findings in schizophrenia have been replicated and, in the last few years, have been followed by systematic fine-mapping efforts to identify positional susceptibility genes. Here, we outline the evidence supporting each of the proposed positional candidate genes and identify some general areas of caution in their interpretation. Several of these findings hold considerable promise both for understanding the neuropathology of this brain disorder, the causes of which remain a mystery, but also for development of novel, mechanism-based treatments for the patients.

A two-stage linkage analysis of Chinese schizophrenia pedigrees in 10 target chromosomes

We performed a two-stage linkage scan involving 25 Chinese schizophrenia families, focusing on 10 target chromosomes which have already been the subject of considerable research. We initially genotyped 237 individuals with 186 markers, five candidate regions were then chosen for fine mapping and 49 additional markers were genotyped. In region 1q21-23, a maximum multipoint HLOD (HLOD=2.38) was observed between D1S484 and D1S2705, under the dominant model. In region 5q35, dominant HOLD of 2.36, 2.04, and 2.31 were found at marker D5S2030, D5S408, and D5S2006, respectively. Consistent multipoint results also supported linkage to this region under the same dominant model, with a highest HOLD of 2.47. Furthermore, single-point HLODs (HLOD=1.95 at D22S274, and HLOD=1.91 at D22S1157) were found in region 22q13, under the dominant model. Evidence from these three regions satisfied the criteria for suggestive linkage and should help in identifying schizophrenia susceptibility genes.

Effect of antipsychotic drugs on DISC1 and dysbindin expression in mouse frontal cortex and hippocampus

Altered expression of Disrupted-In-Schizophrenia-1 (DISC1) and dysbindin (DTNBP1), susceptibility genes for schizophrenia, in schizophrenic brain has been reported; however, the possible effect of antipsychotics on the expression levels of these genes has not yet been studied. We measured the mRNA expression levels of these genes in frontal cortex and hippocampus of mice chronically treated with typical and atypical antipsychotics by a real-time quantitative RT-PCR method. We found that atypical antipsychotics, olanzapine and risperidone, in a clinically relevant dose increased DISC1 expression levels in frontal cortex, while a typical antipsychotic, haloperidol, did not. No significant effect on dysbindin expression levels was observed in either brain region. These data suggest that prior evidence of decreased expression of dysbindin in postmortem brain of schizophrenics is not likely to be a simple artifact of antemortem drug treatment. Our results also suggest a potential role of DISC1 in the therapeutic mechanisms of certain atypical antipsychotics.

Psychosis among "healthy" siblings of schizophrenia patients

BACKGROUND

Schizophrenia aggregates in families and accurate diagnoses are essential for genetic studies of schizophrenia. In this study, we investigated whether siblings of patients with schizophrenia can be identified as free of any psychotic disorder using only register information. We also analyzed the emergence of psychotic disorders among siblings of patients with schizophrenia during seven to eleven years of follow-up.

METHODS

A genetically homogenous population isolate in north-eastern Finland having 365 families with 446 patients with a diagnosis of schizophrenia was initially identified in 1991 using four nationwide registers. Between 1998 and 2002, 124 patients and 183 siblings in 110 families were contacted and interviewed using SCID-I, SCID-II and SANS. We also compared the frequency of mental disorders between siblings and a random population comparison group sample.

RESULTS

Thirty (16%) siblings received a diagnosis of psychotic disorder in the interview. 14 siblings had had psychotic symptoms already before 1991, while 16 developed psychotic symptoms during the follow-up. Over half of the siblings (n = 99, 54%) had a lifetime diagnosis of any mental disorder in the interview.

CONCLUSION

Register information cannot be used to exclude psychotic disorders among siblings of patients with schizophrenia. The high rate of emergence of new psychotic disorders among initially healthy siblings should be taken into account in genetic analysis.

Genes for schizophrenia and bipolar disorder? Implications for psychiatric nosology

It has been conventional for psychiatric research, including the search for predisposing genes, to proceed under the assumption that schizophrenia and bipolar disorder are separate disease entities with different underlying etiologies. These represent Emil Kraepelin's traditional dichotomous classification of the so-called "functional" psychoses and form the basis of modern diagnostic practice. However, findings emerging from many fields of psychiatric research do not fit well with this model. In particular, the pattern of findings emerging from genetic studies shows increasing evidence for an overlap in genetic susceptibility across the traditional classification categories-including association findings at DAOA(G72), DTNBP1 (dysbindin), COMT, BDNF, DISC1, and NRG1. The emerging evidence suggests the possibility of relatively specific relationships between genotype and psychopathology. For example, DISC1 and NRG1 may confer susceptibility to a form of illness with mixed features of schizophrenia and mania. The elucidation of genotype-phenotype relationships is at an early stage, but current findings highlight the need to consider alternative approaches to classification and conceptualization for psychiatric research rather than continuing to rely heavily on the traditional Kraepelinian dichotomy. As psychosis susceptibility genes are identified and characterized over the next few years, this will have a major impact on our understanding of disease pathophysiology and will lead to changes in classification and the clinical practice of psychiatry.

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.

Disrupted In Schizophrenia 1 (DISC1): Subcellular targeting and induction of ring mitochondria

Several independent studies have identified Disrupted In Schizophrenia 1 (DISC1) as a potential susceptibility factor in the pathogenesis of schizophrenia and severe recurrent major depression. To identify potential mechanisms by which DISC1 may influence development of psychiatric illness, we investigated the cellular consequences of recombinant DISC1 expression in COS-7 cells. We show that the N-terminal head domain is sufficient for DISC1 mitochondrial and nuclear targeting, while sequence from the C-terminus facilitates centrosomal association. Loss of C-terminal sequence alters DISC1 subcellular distribution, significantly increasing nuclear localization. DISC1 over-expression produces striking mitochondrial reorganization in some cells, with formation of mitochondrial ring-like structures, indicating a potential involvement of DISC1 in mitochondrial fusion and/or fission.

A functional link between Disrupted-In-Schizophrenia 1 and the eukaryotic translation initiation factor 3

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a candidate gene for schizophrenia. DISC1 is disrupted by a balanced t(1;11)(q42.1;q14.3) translocation segregating with schizophrenia and related psychiatric illness in a large Scottish family. Here, we show that DISC1 interacts via its globular domain with the p40 subunit of the eukaryotic translation initiation factor 3. Furthermore, we found that overexpression of DISC1 in SH-SY5Y cells induces the assembly of eIF3- and TIA-1-positive stress granules (SGs), discrete cytoplasmic granules formed in response to environmental stresses. Our findings suggest that DISC1 may function as a translational regulator and may be involved in stress response.

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.

A schizophrenia-associated mutation of DISC1 perturbs cerebral cortex development

Disrupted-In-Schizophrenia-1 (DISC1), originally identified at the breakpoint of a chromosomal translocation that is linked to a rare familial schizophrenia, has been genetically implicated in schizophrenia in other populations. Schizophrenia involves subtle cytoarchitectural abnormalities that arise during neurodevelopment, but the underlying molecular mechanisms are unclear. Here, we demonstrate that DISC1 is a component of the microtubule-associated dynein motor complex and is essential for maintaining the complex at the centrosome, hence contributing to normal microtubular dynamics. Carboxy-terminal-truncated mutant DISC1 (mutDISC1), which results from a chromosomal translocation, functions in a dominant-negative manner by redistributing wild-type DISC1 through self-association and by dissociating the DISC1-dynein complex from the centrosome. Consequently, either depletion of endogenous DISC1 or expression of mutDISC1 impairs neurite outgrowth in vitro and proper development of the cerebral cortex in vivo. These results indicate that DISC1 is involved in cerebral cortex development, and suggest that loss of DISC1 function may underlie neurodevelopmental dysfunction in schizophrenia.

Screening of PIP5K2A promoter region for mutations in bipolar disorder and schizophrenia

OBJECTIVE

To analyze the promoter region of PIP5K2A, a phosphatidylinositol 4-phosphate 5-kinase that maps to 10p in a region linked to both bipolar disorder and schizophrenia.

METHODS

The promoter region was screened by single-strand conformation polymorphism analysis and DNA sequencing. Allele frequencies were determined in a case-control study. Functional significance of a promoter variant was determined by electromobility gel shift assays.

RESULTS

Homozygosity for a rare putative promoter variant, -1007C-->T, was found in only two patients with schizophrenia and in no controls or bipolar patients. The variant forms a 7/8 base match for the binding site of Oct-1, a member of the POU homeodomain family. Electromobility gel shift assays revealed increased binding of a brain-specific nuclear protein to the -1007T allele compared with -1007C.

CONCLUSION

The data suggest that homozygosity for -1007T could be a rare genetic factor in the development of schizophrenia.

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

DISC1 is expressed in the hippocampus and has been identified as a possible genetic risk factor for both schizophrenia and bipolar disorder. These psychiatric illnesses are associated with impaired learning and memory. This study investigates the association of variation in DISC1 with cognitive function on the same general mental ability test (Moray House Test) at age 11 and age 79, and cognitive change between ages 11 and 79, in 425 people from the Lothian Birth Cohort 1921 (LBC1921). Tests of memory, non-verbal reasoning and executive function were also administered at age 79. The effect of genotype at a non-synonymous single nucleotide polymorphism in exon 11, rs821616, was studied. There was no direct effect of DISC1 genotype on any cognitive measure. However, there was a significant DISC1 genotype by sex interaction on Moray House Test scores at age 79, both before and after adjustment for cognitive ability at age 11 (p = 0.034 and 0.043, respectively). Women homozygous for the Cys allele had significantly lower cognitive ability scores than men at age 79, p = 0.003. Variation in DISC1 may therefore affect cognitive aging especially in women.

Clinical and genetic high-risk strategies in understanding vulnerability to psychosis

Neurodevelopmental processes active during the adolescent period have been hypothesized to participate in the deterioration in functioning associated with the onset of schizophrenia. A number of studies are now underway evaluating individuals in an ultra high-risk clinical state with neuroimaging assessments repeatedly over time, to determine whether particular neural changes predict an imminent onset of psychosis. However, the results of such studies will be difficult to interpret without reference to studies examining the distribution of these neural indicators in the non-clinically-affected first-degree relatives of patients with schizophrenia. Recent work deriving primarily from twin and family studies (i.e., genetic high-risk designs) indicates that some of the alterations in brain function and structure in schizophrenia are primarily genetically mediated and also appear in some of their unaffected first-degree relatives, while other alterations are present in individuals who manifest the illness phenotype but not in relatives at genetic risk. Whereas the primarily genetically mediated deficits shared by at-risk but non-symptomatic relatives are not likely to show differential change in the premorbid period, and may be necessary but clearly not sufficient for the development of psychotic symptoms, the deficits specific to patients who manifest the illness phenotype are good candidates for marking the neurobiological processes associated with the emergence of psychotic symptoms at the time of schizophrenia onset. Preliminary results from longitudinal studies of individuals ascertained initially in a prodromal (i.e., "clinical high-risk") state appear to be interpretable within this framework.

Prevalence and diagnosis of schizophrenia based on register, case record and interview data in an isolated Finnish birth cohort born 1940-1969

INTRODUCTION

Schizophrenia occurs worldwide but the prevalence varies markedly. In Finland, schizophrenia is most prevalent in the northeastern region. Our aims were to reassess the register-, case record- and interview-based lifetime prevalence in a genetically homogeneous birth cohort from an isolate population with earlier reported high prevalence of schizophrenia and a chromosome linkage to chromosome 1q.

METHODS

We identified all patients with a diagnosis of schizophrenia [International Classification of Diseases (ICD)-8, ICD-9 or ICD-10 codes], born 1940-1969 in the isolate (n=282) and alive (n=237) in 1998 using the Hospital Discharge, Disability Pension and Free Medicine Registers. The corresponding birth cohort of 14,817 persons and 12,368 alive in 1998 was identified from the National Population Register. We validated 69% of the register diagnosis by making DSM-IV consensus diagnoses, and interviewed 131 (55%) of the 237 patients with SCID-I and SCID-II.

RESULTS

The register-based lifetime prevalence was 1.5% for schizophrenia and 1.9% for schizophrenia spectrum psychotic disorders: in birth cohorts born 1945 to 1959, the latter prevalence was especially high (2.4%). Of those with a register diagnosis of schizophrenia spectrum psychotic disorder, 69% or 63% also received a record-based consensus diagnosis or SCID interview diagnosis of schizophrenia, and the prevalence was 0.9-1.3 and 0.7-1.2%, respectively, when we reassessed most of the register-based cases. The cumulative incidence of schizophrenia spectrum psychotic disorders in the total birth cohort was 1.9%.

CONCLUSION

In this isolate, the register, DSM-IV consensus and SCID interview-based lifetime prevalence of schizophrenia was internationally high. For genetic research work, the register diagnosis should be reassessed using either structured interview or the best estimate consensus diagnosis.

Schizophrenia: genes at last?

Genetic epidemiological studies suggest that individual variation in susceptibility to schizophrenia is largely genetic, reflecting alleles of moderate to small effect in multiple genes. Molecular genetic studies have identified several potential regions of linkage and two associated chromosomal abnormalities, and evidence is accumulating in favour of several positional candidate genes. Currently, the positional candidate genes for which we consider the evidence to be strong are those encoding dysbindin (DTNBP1) and neuregulin 1 (NRG1). For other genes, disrupted in schizophrenia 1 (DISC1), D-amino-acid oxidase (DAO), D-amino-acid oxidase activator (DAOA, formerly known as G72) and regulator of G-protein signalling 4 (RGS4), the data are promising but not yet compelling. The identification of these, and other susceptibility genes, will open up new avenues for research aimed at understanding the pathogenesis of schizophrenia, and will catalyse a re-appraisal of the classification of psychiatric disorders.

DISC1 and neurocognitive function in schizophrenia

We recently reported an association between DISC1 and schizophrenia, schizoaffective disorder, and bipolar disorder. Convergent evidence suggests that DISC1 has a direct effect on central nervous system functioning. However, there is a paucity of data investigating the effects of DISC1 on neurocognition. Thus, we analyzed the relationship between five single-nucleotide polymorphisms that influenced risk for schizophrenia in our previous study and neurocognition in 250 patients with schizophrenia. DISC1 genotype was related to neurocognitive performance on measures of rapid visual search and verbal working memory, when controlling for age and premorbid intellectual capacity, and explained 3%-4% of the variance. These data suggest that DISC1 is associated with neurocognitive functioning in schizophrenia.

A frameshift mutation in Disrupted in Schizophrenia 1 in an American family with schizophrenia and schizoaffective disorder

In a large Scottish pedigree, a balanced translocation t(1;11)(q42.1;q14.3) segregates with major mental illness, including schizophrenia, bipolar disorder, and recurrent major depression. The translocation is predicted to result in the loss of the C-terminal region of the protein product of Disrupted In SChizophrenia 1 (DISC1), a gene located on 1q42.1. Since this initial discovery, DISC1 has been functionally implicated in several processes, including neurodevelopment. Based on the genetic and functional evidence that DISC1 may be associated with schizophrenia, we sequenced portions of DISC1 in 28 unrelated probands with schizophrenia and six unrelated probands with schizoaffective disorder, ascertained as part of a large sibpair study. We detected a 4 bp deletion at the extreme 3' end of exon 12 in a proband with schizophrenia. The mutation was also present in a sib with schizophrenia, a sib with schizoaffective disorder, and the unaffected father, while the mutation was not detected in 424 control individuals. The mutation is predicted to cause a frameshift and encode a truncated protein with nine abnormal C-terminal amino acids. The truncated transcript is detectable, but at a reduced level, in lymphoblastoid cell lines from three of four mutation carriers. These findings are consistent with the possibility that mutations in the DISC1 gene can increase the risk for schizophrenia and related disorders.

Association between the TRAX/DISC locus and both bipolar disorder and schizophrenia in the Scottish population

The Translin-associated factor X/Disrupted in Schizophrenia 1 (TRAX/DISC) region was first implicated as a susceptibility locus for schizophrenia by analysis of a large Scottish family in which a t(1;11) translocation cosegregates with schizophrenia, bipolar disorder and recurrent major depression. We now report evidence for association between bipolar disorder and schizophrenia and this locus in the general Scottish population. A systematic study of linkage disequilibrium in a representative sample of the Scottish population was undertaken across the 510 kb of TRAX and DISC1. SNPs representing each haplotype block were selected for case-control association studies of both schizophrenia and bipolar disorder. Significant association with bipolar disorder in women P=0.00026 (P=0.0016 in men and women combined) was detected in a region of DISC1. This same region also showed nominally significant association with schizophrenia in both men and women combined, P=0.0056. Two further regions, one in TRAX and the second in DISC1, showed weaker evidence for sex-specific associations of individual haplotypes with bipolar disorder in men and women respectively, P<0.01. Only the association between bipolar women and DISC1 remained significant after correction for multiple testing. This result provides further supporting evidence for DISC1 as a susceptibility factor for both bipolar disorder and schizophrenia, consistent with the diagnoses in the original Scottish translocation family.

Genetic models of schizophrenia and bipolar disorder: overlapping inheritance or discrete genotypes?

Schizophrenia and affective disorder have been considered to be nosologically and etiologically distinct disorders. This postulate is challenged by progress in new biological research. Both disorders are strongly influenced by genetic factors; thus genetic research is a main contributor to this discussion. We review current evidence of the genetic relationship between schizophrenia and affective disorders, mainly bipolar disorder (the various genetic research methods have been particularly applied to bipolar disorder). Recent family and twin studies reveal a growing consistency in demonstrating cosegregation between both disorders which is difficult to detect with certainty given the low base rates. Systematic molecular genetic search for specific genes impacting on either disorder has now identified one gene which is apparently involved in both disorders (G72/G30); other candidate genes reveal some evidence to present as susceptibility genes with very modest effects for each of both disorders, although not consistently so (e. g., COMT, BDNF). There is room for speculation about other common susceptibility genes, given the overlap between candidate regions for schizophrenia and those for bipolar disorder emerging from linkage studies.

Finding schizophrenia genes

Genetic epidemiological studies suggest that individual variation in susceptibility to schizophrenia is largely genetic, reflecting alleles of moderate to small effect in multiple genes. Molecular genetic studies have identified a number of potential regions of linkage and 2 associated chromosomal abnormalities, and accumulating evidence favors several positional candidate genes. These findings are grounds for optimism that insight into genetic factors associated with schizophrenia will help further our understanding of this disease and contribute to the development of new ways to treat it.

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.

Tumor necrosis factor promoter haplotype associated with schizophrenia reveals a linked locus on 1q44

Using restriction fragment length polymorphism and pyrosequencing methods, we genotyped two TNFA gene promoter SNPs (-G308A, -G238A) and analyzed the haplotype structure in 24 Canadian families of primarily Celtic origin. Our results demonstrate that after correction for multiple testing based on simulations of 10 000 replicates of unlinked/unassociated data, there is evidence for association (P=0.026) of a specific haplotype (-308A, -238G) with schizophrenia and schizophrenia spectrum disorders with a family-based trimmed haplotype linkage disequilibrium test (Trimhap). Stratifying the 22 families with genome scan data by TNFA promoter haplotypes followed by reanalysis of linkage to schizophrenia throughout the genome, we identified few loci that exhibit a considerable increase in LOD/HLOD scores. A locus on chromosome 1q44 (D1S1609) demonstrated a significant increase (P=0.025) in LOD score from 0.15 to 3.01 with a broad definition of the schizophrenia phenotype and a dominant mode of inheritance. This result replicates a previously reported positive result of linkage of schizophrenia spectrum disorders to this area of the genome. We also illustrated that simulation studies are pivotal in evaluating the significance of results obtained with newer statistical methods, when multiple, but not independent, tests are performed, and when sample stratification is utilized to reduce the impact of heterogeneity or assess the interaction between loci.

The inheritance of intermediate phenotypes for schizophrenia

PURPOSE OF REVIEW

While schizophrenia is substantially heritable, the mode of inheritance is complex, involving numerous genes of small effect and a non-trivial environmental component. The 'endophenotype' approach is an alternative method for measuring phenotypic variation that may facilitate the identification of susceptibility genes in the context of complexly inherited traits. Here we review recent studies applying this method to measures of brain structure, physiology, and function in samples of schizophrenia patients and their non-ill first-degree relatives (siblings and co-twins).

RECENT FINDINGS

The results suggest that there are multiple heritable dimensions of central nervous system pathology in schizophrenia, including disturbances in the structure and functioning of frontal lobe systems involved in working memory and executive processes, temporal lobe systems involved in episodic memory, auditory perception, and language processing, and cortical and sub-cortical systems mediating smooth pursuit eye movements and sensorimotor gating. A number of genetic loci that are suspected to play a role in predisposing to schizophrenia, including the DISC1, COMT, neuregulin, dysbindin, and alpha-7 nicotinic receptor genes, appear to affect quantitative variation on one or more of these indicators.

SUMMARY

Future work is encouraged to address whether each of these neural system dysfunctions are under the influence of a partially distinct set of genes, to elucidate the manner in which multiple genes may coalesce in determining schizophrenia-promoting dysfunction in each neurobehavioral domain, and to clarify the degree of overlap in these quantitative trait loci-endophenotype relationships with other forms of psychosis, particularly bipolar disorder.

Cytogenetics and gene discovery in psychiatric disorders

The disruption of genes by balanced translocations and other rare germline chromosomal abnormalities has played an important part in the discovery of many common Mendelian disorder genes, somatic oncogenes and tumour supressors. A search of published literature has identified 15 genes whose genomic sequences are directly disrupted by translocation breakpoints in individuals with neuropsychiatric illness. In these cases, it is reasonable to hypothesise that haploinsufficiency is a major factor contributing to illness. These findings suggest that the predicted polygenic nature of psychiatric illness may not represent the complete picture; genes of large individual effect appear to exist. Cytogenetic events may provide important insights into neurochemical pathways and cellular processes critical for the development of complex psychiatric phenotypes in the population at large.

A form of DISC1 enriched in nucleus: altered subcellular distribution in orbitofrontal cortex in psychosis and substance/alcohol abuse

Disrupted-In-Schizophrenia 1 (DISC1) was identified as the sole gene whose ORF is truncated and cosegregates with major mental illnesses in a Scottish family. DISC1 has also been suggested, by association and linkage studies, to be a susceptibility gene for schizophrenia (SZ) in independent populations. However, no analysis of DISC1 protein in human brains, especially those of patients with SZ, has yet been conducted. Here we performed a biochemical analysis of DISC1 protein in a well characterized set of autopsied brains, including brains of patients with SZ, bipolar disorder, and major depression (MD), as well as normal control brains. We identified an isoform of DISC1 by using MS and demonstrated that it is enriched in the nucleus of HeLa cells. In the orbitofrontal cortex, the subcellular distribution of this DISC1 isoform, assessed by the nuclear to cytoplasmic ratio in the immunoreactivity of the isoform, is significantly changed in brains from patients with SZ and MD. This altered distribution is also observed in those subjects with substance and alcohol abuse. The changes in MD brains are significantly influenced by substance/alcohol abuse as well as postmortem interval; however, the alteration in SZ brains is free from brain-associated confounding factors, although an interaction with substance/alcohol abuse cannot be completely ruled out. These results suggest that DISC1 may be implicated in psychiatric conditions in other populations than the unique Scottish family.

Expanding the 'central dogma': the regulatory role of nonprotein coding genes and implications for the genetic liability to schizophrenia

It is now evident that nonprotein coding RNA (ncRNA) plays a critical role in regulating the timing and rate of protein translation. The potential importance of ncRNAs is suggested by the observation that the complexity of an organism is poorly correlated with its number of protein coding genes, yet highly correlated with its number of ncRNA genes, and that in the human genome only a small fraction (2-3%) of genetic transcripts are actually translated into proteins. In this review, we discuss several examples of known RNA mechanisms for the regulation of protein synthesis. We then discuss the possibility that ncRNA regulation of schizophrenia risk genes may underlie the diverse findings of genetic linkage studies including that protein-altering gene polymorphisms are not generally found in schizophrenia. Thus, inadequate or mistimed expression of a functional protein may occur either due to mutation or other dysfunction of the DNA coding base pair sequence, leading to a dysfunctional protein, or due to post-transcriptional events such as abnormal ncRNA regulation of a normal gene. One or more 'schizophrenia disease genes' may turn out to include abnormal transcriptional units that code for RNA regulators of protein coding gene expression or to be proximal to such units, rather than to be abnormalities in the protein coding gene itself. Understanding the genetics of schizophrenia and other complex neuropsychiatric disorders might very well include consideration of RNA and epigenetic regulation of protein expression in addition to polymorphisms of the protein coding gene.

Schizophrenia genes, gene expression, and neuropathology: on the matter of their convergence

This review critically summarizes the neuropathology and genetics of schizophrenia, the relationship between them, and speculates on their functional convergence. The morphological correlates of schizophrenia are subtle, and range from a slight reduction in brain size to localized alterations in the morphology and molecular composition of specific neuronal, synaptic, and glial populations in the hippocampus, dorsolateral prefrontal cortex, and dorsal thalamus. These findings have fostered the view of schizophrenia as a disorder of connectivity and of the synapse. Although attractive, such concepts are vague, and differentiating primary events from epiphenomena has been difficult. A way forward is provided by the recent identification of several putative susceptibility genes (including neuregulin, dysbindin, COMT, DISC1, RGS4, GRM3, and G72). We discuss the evidence for these and other genes, along with what is known of their expression profiles and biological roles in brain and how these may be altered in schizophrenia. The evidence for several of the genes is now strong. However, for none, with the likely exception of COMT, has a causative allele or the mechanism by which it predisposes to schizophrenia been identified. Nevertheless, we speculate that the genes may all converge functionally upon schizophrenia risk via an influence upon synaptic plasticity and the development and stabilization of cortical microcircuitry. NMDA receptor-mediated glutamate transmission may be especially implicated, though there are also direct and indirect links to dopamine and GABA signalling. Hence, there is a correspondence between the putative roles of the genes at the molecular and synaptic levels and the existing understanding of the disorder at the neural systems level. Characterization of a core molecular pathway and a 'genetic cytoarchitecture' would be a profound advance in understanding schizophrenia, and may have equally significant therapeutic implications.

A genome scan and follow-up study identify a bipolar disorder susceptibility locus on chromosome 1q42

In this study, we report a genome scan for psychiatric disease susceptibility loci in 13 Scottish families. We follow up one of the linkage peaks on chromosome 1q in a substantially larger sample of 22 families affected by schizophrenia (SCZ) or bipolar affective disorder (BPAD). To minimise the effect of genetic heterogeneity, we collected mainly large extended families (average family size >18). The families collected were Scottish, carried no chromosomal abnormalities and were unrelated to the large family previously reported as segregating a balanced (1:11) translocation with major psychiatric disease. In the genome scan, we found linkage peaks with logarithm of odds (LOD) scores >1.5 on chromosomes 1q (BPAD), 3p (SCZ), 8p (SCZ), 8q (BPAD), 9q (BPAD) and 19q (SCZ). In the follow-up sample, we obtained most evidence for linkage to 1q42 in bipolar families, with a maximum (parametric) LOD of 2.63 at D1S103. Multipoint variance components linkage gave a maximum LOD of 2.77 (overall maximum LOD 2.47 after correction for multiple tests), 12 cM from the previously identified SCZ susceptibility locus DISC1. Interestingly, there was negligible evidence for linkage to 1q42 in the SCZ families. These results, together with results from a number of other recent studies, stress the importance of the 1q42 region in susceptibility to both BPAD and SCZ.

Expression of disrupted in schizophrenia 1 (DISC1) protein in the adult and developing mouse brain indicates its role in neurodevelopment

Disrupted in Schizophrenia 1 (DISC1) was identified as a potential susceptibility gene for schizophrenia due to its disruption by a balanced t(1;11) (q42;q14) translocation, which has been shown to cosegregate with major psychiatric disease in a large Scottish family. We have recently presented evidence that DISC1 exists in a neurodevelopmentally regulated protein complex with Nudel. In this study, we report the protein expression profile of DISC1 in the adult and developing mouse brain utilizing immunohistochemistry and quantitative Western blot. In the adult mouse brain, DISC1 is expressed in neurons within various brain areas including the olfactory bulb, cortex, hippocampus, hypothalamus, cerebellum and brain stem. During development, DISC1 protein is detected at all stages, from E10 to 6 months old, with two significant peaks of protein expression of a DISC1 isoform at E13.5 and P35. Interestingly, these time points correspond to critical stages during mouse development, the active neurogenesis period in the developing brain and the period of puberty. Together, these results suggest that DISC1 may play a critical role in brain development, consistent with the neurodevelopmental hypothesis of the etiology of schizophrenia.

Association study of polymorphisms in the 5' upstream region of human DISC1 gene with schizophrenia

Disrupted-in-Schizophrenia-1 (DISC1) is a gene in which a mutant truncation by a balanced t(1;11)(p42.1;q14.3) translocation is segregated with major psychiatric illness with a predominance of schizophrenic symptomatology in a large Scottish family. However, no functional polymorphisms have been detected that are associated with schizophrenia in general populations. As prior polymorphism searches in DISC1 have been focused on coding exons and flanking introns, the present study examined sequence variations in the 5' upstream region of DISC1. Screening of exon 1 through to approximately 1.0 kb upstream of exon 1 identified 6 polymorphisms, including 2 novel variants, -94C>A and -199(CG)(n). We tested these variants for associations with schizophrenia in the first set of a case (n = 198) and control (n = 198) panel, and found significant results with -274G>C (genotypic P = 0.01) and -215(TG)(n) (genotypic P = 0.039). However, we failed to replicate these associations in a second, larger independent patient (n = 532) and control (n = 519) sample. These results suggest that the genomic interval of DISC1 probably involved in transcriptional regulation does not display major genetic relevance in Japanese schizophrenia patients.

Disrupted in schizophrenia 1 (DISC1): association with schizophrenia, schizoaffective disorder, and bipolar disorder

Schizophrenia, schizoaffective disorder, and bipolar disorder are common psychiatric disorders with high heritabilities and variable phenotypes. The Disrupted in Schizophrenia 1 (DISC1) gene, on chromosome 1q42, was originally discovered and linked to schizophrenia in a Scottish kindred carrying a balanced translocation that disrupts DISC1 and DISC2. More recently, DISC1 was linked to schizophrenia, broadly defined, in the general Finnish population, through the undertransmission to affected women of a common haplotype from the region of intron 1/exon 2. We present data from a case-control study of a North American white population, confirming the underrepresentation of a common haplotype of the intron 1/exon 2 region in individuals with schizoaffective disorder. Multiple haplotypes contained within four haplotype blocks extending between exon 1 and exon 9 are associated with schizophrenia, schizoaffective disorder, and bipolar disorder. We also find overrepresentation of the exon 9 missense allele Phe607 in schizoaffective disorder. These data support the idea that these apparently distinct disorders have at least a partially convergent etiology and that variation at the DISC1 locus predisposes individuals to a variety of psychiatric disorders.

Replication of 1q42 linkage in Finnish schizophrenia pedigrees

Chromosome 1q has been implicated in the etiology of schizophrenia in several independent studies. However, the peak linkage findings have been dispersed over a large chromosomal region, with negative findings in this region also being reported. Our group has previously observed linkage on chromosome 1q42, maximizing within the DISC1 gene, which has also been implied in the etiology of schizophrenia based on functional studies. In the study presented here, we genotyped 300 polymorphic markers on chromosome 1 using a study sample of 70 families with multiple individuals affected with schizophrenia or related conditions, independent of the study samples in our previous reports. We again found evidence for linkage on 1q42 maximizing within the DISC1 gene (rs1000731, lod=2.70). Further, a haplotype containing the most strongly linked markers showed some evidence of association with the disease. This replicates the previous linkage finding in the same region and constitutes supportive evidence for a susceptibility gene in this region.

Age at onset and cognitive functioning in schizophrenia

BACKGROUND

Impairments in cognitive functioning are common in schizophrenia, and the degree of impairment may be associated with the individual's age at onset of the disorder.

AIMS

To examine the effect of age at onset on cognitive functioning using the California Verbal Learning Test, sub-tests from the Wechsler Memory Scale-Revised and sub-scales from the Wechsler Adult Intelligence Scale-Revised among families with schizophrenia.

METHOD

The effect of age at onset on cognitive function in 237 people with schizophrenia from a population-based sample was examined using linear mixed effects models with family as the random effect, and age, gender, chronicity of the illness and number of affected first-degree relatives as fixed effects.

RESULTS

Impairment in verbal learning and memory was associated with earlier disease onset. No association was found for working memory or IQ.

CONCLUSIONS

In patients with early-onset schizophrenia, verbal memory functions in particular should be taken into account in neuropsychological evaluation and efforts at remediation.

Disrupted in Schizophrenia 1 (DISC1) is a multicompartmentalized protein that predominantly localizes to mitochondria

DISC1 is disrupted by a chromosomal translocation cosegregating with schizophrenia and recurrent major depression in a large Scottish family and has also been reported as a potential susceptibility locus in independent populations. We reveal a widespread and complex pattern of DISC1 expression, with at least five forms of Disrupted in Schizophrenia 1 DISC1 detectable. Mitochondria are the predominant site of DISC1 expression with additional nuclear, cytoplasmic, and actin-associated locations evident. Although the subcellular targeting of DISC1 is clearly complex, the association with mitochondria is of interest as many mitochondrial deficits have been reported in schizophrenia and other neuropsychiatric illnesses. Moreover, of the many cellular functions performed by mitochondria, their role in oxidative phosphorylation, calcium homeostasis, and apoptosis may hold particular relevance for the neuronal disturbances believed to be involved in the pathogenesis of schizophrenia.

Identification of PIK3C3 promoter variant associated with bipolar disorder and schizophrenia

BACKGROUND

Genes involved in phosphoinositide (PI) lipid metabolism are excellent candidates to consider in the pathogenesis of bipolar disorder (BD) and schizophrenia (SZ). One is PIK3C3, a member of the phosphatidylinositide 3-kinase family that maps closely to markers on 18q linked to both BD and SZ in a few studies.

METHODS

The promoter region of PIK3C3 was analyzed for mutations by single-strand conformation polymorphism analysis and sequencing. A case-control association study was conducted to determine the distribution of variant alleles in unrelated patients from three cohorts. Electromobility gel shift assays (EMSA) were performed to assess the functional significance of variants.

RESULTS

Two polymorphisms in complete linked disequilibrium with each other were identified, -432C- > T and a "C" insert at position -86. The -432T allele occurs within an octamer containing an ATTT motif resembling members of the POU family of transcription factors. In each population analyzed, an increase in -432T was found in patients. EMSAs showed that a -432T containing oligonucleotide binds to brain proteins that do not recognize -432C.

CONCLUSIONS

A promoter mutation in a PI regulator affecting the binding of a POU-type transcription factor may be involved in BD and SZ in a subset of patients.

DISC1 localizes to the centrosome by binding to kendrin

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a novel gene disrupted by a (1;11)(q42.1;q14.3) translocation that segregated with major mental disorders in a Scottish family. Using the yeast two-hybrid system, we screened a human brain cDNA library for interactors of the DISC1 protein. One of the positive clones encoded kendrin/pericentrin-B, a giant protein known to localize specifically to the centrosome. The interaction between DISC1 and kendrin in mammalian cells was demonstrated by an immunoprecipitation assay. Residues 446-533 of DISC1 were essential for the interaction with kendrin. Immunocytochemical analysis revealed the colocalization of DISC1 and kendrin to the centrosome. These data indicate that DISC1 localizes to the centrosome by binding to kendrin. Kendrin has been reported to anchor the gamma-tubulin complex to the centrosome, providing microtubule nucleation sites. The present study suggests the possible involvement of DISC1 in the pathophysiology of mental disorders due to its putative effect on centrosomal function.

Clinical phenotype of schizophrenia in a Finnish isolate

We identified all cases in Finland (population of 5 million) with a diagnosis of schizophrenia born between 1940 and 1969, using four national computerised registers with high reliability. A sample of 397 families was identified in a genetically homogeneous internal isolate (population of 18,000) in northeastern Finland with high prevalence for schizophrenia and an LOD score of 3.8 in chromosome 1. Our aim was to examine with Operational Criteria Checklist for Psychotic Illness (OCCPI) factor analysis the psychotic and affective signs and symptoms of schizophrenia in this genetically homogeneous population, and compare them with findings from individuals with schizophrenia from multiplex families from the whole country. After collecting all original case notes, we made DSM-IV consensus diagnoses and completed OCCPI ratings on a lifetime basis. For the factor analysis, we accepted 190 patients with a diagnosis of schizophrenia. In addition, 466 schizophrenia patients from 147 multiplex families from the whole country were included in the analysis. The OCCPI factor analysis resulted in four factors: "delusions and hallucinations" and "negative" factors, plus two affective ("manic" and "depressive") factors. We compared the pattern of symptoms among three patient groups: isolate patients who were the only affected individuals in their family, isolate patients who had affected family members, and patients from the whole country with affected family members. We found no clear differences among these groups. However, there were significant differences in the frequency of individual OCCPI items between the study groups. Findings in this schizophrenia OCCPI phenotype study suggest that the clinical picture of schizophrenia in a genetically isolated and homogeneous population closely resembles our nationwide findings in Finland.

Yeast two-hybrid screens implicate DISC1 in brain development and function

DISC1 is a candidate gene for involvement in the aetiology of major psychiatric illnesses including schizophrenia. We report here the results of DISC1 yeast two-hybrid screens using human foetal and adult brain libraries. Twenty-one proteins from a variety of subcellular locations were identified, consistent with observations that DISC1 occupies multiple subcellular compartments. The cellular roles of the proteins identified implicate DISC1 in several aspects of central nervous system development and function, including gene transcription, mitochondrial function, modulation of the actin cytoskeleton, neuronal migration, glutamate transmission, and signal transduction. Intriguingly, mutations in one of the proteins identified, WKL1, have been previously suggested to underlie the aetiology of catatonic schizophrenia.

Disrupted in Schizophrenia 1 and Nudel form a neurodevelopmentally regulated protein complex: implications for schizophrenia and other major neurological disorders

Disrupted In Schizophrenia 1 (DISC1) was identified as a potential susceptibility gene for schizophrenia due to its disruption by a balanced t(1;11) (q42;q14) translocation, which has been shown to cosegregate with major psychiatric disease in a large Scottish family. We have demonstrated that DISC1 exists in a neurodevelopmentally regulated protein complex with Nudel. The complex is abundant at E17 and in early postnatal life but is greatly reduced in the adult. Nudel has previously been shown to bind Lis1, a gene underlying lissencephaly in humans. Critically, we show that the predicted peptide product resulting from the Scottish translocation removes the interaction domain for Nudel. DISC1 interacts with Nudel through a leucine zipper domain and binds to a novel DISC1-interaction domain on Nudel, which is independent from the Lis1 binding site. We show that Nudel is able to act as a bridge between DISC1 and Lis1 to allow formation of a trimolecular complex. Nudel has been implicated to play a role in neuronal migration, together with the developmental variation in the abundance of the DISC1-Nudel complex, may implicate a defective DISC1-Nudel complex as a neurodevelopmental cause of schizophrenia.

DISC1 and DISC2: discovering and dissecting molecular mechanisms underlying psychiatric illness

A balanced (1;11)(q42;q14) translocation co-segregates with schizophrenia and major affective disorders in a large Scottish family. The translocation breakpoint on chromosome 1 is located within the Disrupted in Schizophrenia 1 and 2 genes (DISC1 and DISC2). Consequently loss of normal function of these genes is likely to underlie the susceptibility to developing psychiatric disorders that is conferred by inheritance of the translocation. Additionally, a number of independent genetic studies highlight the region of chromosome 1q containing DISC1 and DISC2 as a likely susceptibility locus for both schizophrenia and affective disorders. These genes are thus implicated in the aetiology of major psychiatric disorders in several populations. Although the function of DISC1 was initially unknown, several recent reports have made significant progress towards understanding its role in the central nervous system. Intriguingly, all data obtained to date point towards an involvement in processes critical to neurodevelopment and function. DISC2 has not been studied in detail, but is likely to modulate DISC1 expression. Overall, it is clear from the combination of genetic and functional data that DISC1 and/or DISC2 are emerging as important factors in the molecular genetics of psychiatric illness.

Expression of disrupted-in-schizophrenia-1, a schizophrenia-associated gene, is prominent in the mouse hippocampus throughout brain development

DISC1 (Disrupted-In-Schizophrenia 1) has been associated with schizophrenia in multiple genetic studies. Studies from our laboratory have shown that Disc1, the mouse ortholog of DISC1, is highly expressed in the dentate gyrus of the hippocampus in the adult mouse brain. Because developmental dysfunction of the hippocampus is thought to play a major role in schizophrenia pathogenesis, and the dentate gyrus is a major locus for adult neurogenesis in the mouse, we investigated Disc1 expression during mouse brain development. Strikingly, Disc1 is strongly expressed in the hippocampus during all stages of hippocampal development, from embryonic day 14 through adulthood. Disc1 mRNA was detected in the dentate gyrus at all stages in which this structure was identifiable, as well as in the cornu ammonis (CA) fields of the hippocampus, the subiculum and adjacent entorhinal cortex, and the developing cerebral neocortex, hypothalamus, and olfactory bulbs, all of which also express Disc1 in the adult mouse brain. In addition, Disc1 mRNA was seen in regions of the developing mouse brain which do not express Disc1 during adulthood, regions including the bed nucleus of the stria terminalis, reticular thalamic nucleus and reuniens thalamic nucleus. These results demonstrate that Disc1 marks the hippocampus from its earliest stages, and suggest that developmental Disc1 dysfunction may lead to defects in hippocampal function that are associated with schizophrenia.

Clinical phenotypes associated with DISC1, a candidate gene for schizophrenia

Genetic factors play an important part in the development of schizophrenia and bipolar disorder, and linkage analyses in families have successfully identified several chromosomal regions containing candidate genes. A single large pedigree has been described in which schizophrenia and depression segregate with a balanced chromosomal translocation involving the long arm of chromosome 1 and the short arm of chromosome 11. The gene named DISC1, disrupted at the chromosome 1 breakpoint, is a novel candidate gene that may have a role in the pathogenesis of schizophrenia. The cellular location and function of the protein coded by DISC1 is currently being investigated. The phenotype associated with DISC1 in the t (1;11) translocation family includes schizophrenia, schizoaffective disorder, recurrent major depression and bipolar disorder. Hence this locus is one of several now reported apparently showing linkage to both schizophrenia and bipolar disorder. The study of intermediate phenotypes or "endophenotypes" may clarify the relations between phenotype and genotype. Auditory event related potentials are EEG based physiological measures widely studied in schizophrenia. In particular the cognitive evoked potential, the P300 response generated during an "odd-ball" two-tone discrimination task consistently shows reduced amplitude in schizophrenia compared to controls. In members of the family with the t (1;11) translocation, P300 amplitude was reduced in relatives who carried the translocation compared to relatives with a normal karyotype. Furthermore the amplitude reduction was independent of the presence or absence of symptoms because asymptomatic translocation carriers showed similar P300 amplitude reduction as was found in translocation carriers who were diagnosed with schizophrenia, bipolar disorder or unipolar depression. The results confirm that subjects with schizophrenia who carry the t (1;11) translocation have similar phenotype to unrelated subjects with schizophrenia and a normal karyotype. Furthermore P300 amplitude may be a useful intermediate phenotype detecting the neuropathology of schizophrenia in "at risk" individuals even in the absence of clinical symptoms.

Haplotype analysis and identification of genes for a complex trait: examples from schizophrenia

For more than a decade there has been intensive research into the genetic etiology of schizophrenia, yet it is only recently that the first findings of promising genes associating with the disorder have been reported. Linkage analyses in families collected from different populations have provided relatively well defined genomic loci. These have been typically followed by fine mapping studies using single nucleotide polymorphisms (SNPs). A number of analysis programs have been produced to test SNPs and their haplotypes for association. Typically association has been established to specific haplotypes representing an allelic variant of the corresponding gene. The inherent problem of multiple testing in the analysis of haplotypes needs to be addressed fully, to determine if any of these recent findings can be considered as confirmed susceptibility genes for schizophrenia. However, informative haplotypes have provided a way to define allelic variants of genes associated with schizophrenia in numerous study samples, and are a useful tool in characterizing the extent of allelic diversity of putative schizophrenia susceptibility genes within different populations.

Polymorphism screening of PIP5K2A: a candidate gene for chromosome 10p-linked psychiatric disorders

Lithium is a potent noncompetitive inhibitor of inositol monophosphatases, enzymes involved in phosphoinositide (PI) and inositol phosphate metabolism. A critical component of the PI pathway is phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)), which is hydrolyzed to second messengers and has a direct role in synaptic vesicle function. Interestingly, a number of genes involved in the synthesis and dephosphorylation of PtdIns(4,5)P(2) are found in regions of the genome previously mapped in bipolar disorder (BD) including 10p12, 21q22, and 22q11, among others. Some of these regions overlap with loci mapped in schizophrenia (SZ). One gene involved in PI metabolism that maps to a region of interest is 10p12-linked PIP5K2A, a member of the phosphatidylinositol 4-phosphate 5-kinase family. Polymorphism screening revealed the existence of an imperfect CT repeat polymorphism located near the exon 9-intron 9 splice donor site. A modest difference was found in the distribution of alleles from this highly polymorphic variant when bipolar and schizophrenic subjects were compared with controls; relatively rare short repeat variants were found more commonly in patients and homozygosity for a common long repeat variant was found more commonly in controls. These data suggest that the imperfect CT repeat in PIP5K2A intron 9 should be further investigated as a possible candidate allele for 10p12-linked psychiatric disorders.