A t(1;11) translocation linked to schizophrenia and affective disorders gives rise to aberrant chimeric DISC1 transcripts that encode structurally altered, deleterious mitochondrial proteins.

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a risk factor for psychiatric illness through its disruption by a balanced chromosomal translocation, t(1;11)(q42.1;q14.3), that co-segregates with schizophrenia, bipolar disorder and depression. We previously reported that the translocation reduces DISC1 expression, consistent with a haploinsufficiency disease model. Here we report that, in lymphoblastoid cell lines, the translocation additionally results in the production of abnormal transcripts due to the fusion of DISC1 with a disrupted gene on chromosome 11 (DISC1FP1/Boymaw). These chimeric transcripts encode abnormal proteins, designated CP1, CP60 and CP69, consisting of DISC1 amino acids 1-597 plus 1, 60 or 69 amino acids, respectively. The novel 69 amino acids in CP69 induce increased α-helical content and formation of large stable protein assemblies. The same is predicted for CP60. Both CP60 and CP69 exhibit profoundly altered functional properties within cell lines and neurons. Both are predominantly targeted to mitochondria, where they induce clustering and loss of membrane potential, indicative of severe mitochondrial dysfunction. There is currently no access to neural material from translocation carriers to confirm these findings, but there is no reason to suppose that these chimeric transcripts will not also be expressed in the brain. There is thus potential for the production of abnormal chimeric proteins in the brains of translocation carriers, although at substantially lower levels than for native DISC1. The mechanism by which inheritance of the translocation increases risk of psychiatric illness may therefore involve both DISC1 haploinsufficiency and mitochondrial deficiency due to the effects of abnormal chimeric protein expression. GenBank accession numbers: DISC1FP1 (EU302123), Boymaw (GU134617), der 11 chimeric transcript DISC1FP1 exon 2 to DISC1 exon 9 (JQ650115), der 1 chimeric transcript DISC1 exon 4 to DISC1FP1 exon 4 (JQ650116), der 1 chimeric transcript DISC1 exon 6 to DISC1FP1 exon 3a (JQ650117).

GRIK4/KA1 protein expression in human brain and correlation with bipolar disorder risk variant status.

The kainate class of ionotropic glutamate receptors is involved in the regulation of neuronal transmission and synaptic plasticity. Previously we reported that a deletion variant within the gene GRIK4, which encodes the KA1 kainate receptor subunit, was associated with a reduced risk of bipolar disorder and increased GRIK4 mRNA abundance. Using a high resolution immunohistochemistry technique, we characterized KA1 protein localization in human brain and performed a genotype-protein expression correlation study. KA1 was expressed in specific populations of neuronal cells in the cerebellum and all layers of the frontal and parahippocampal cortices. In the hippocampus, strong KA1 expression was observed in the stratum pyramidale and stratum lucidum of CA3 and CA2, in cell processes in CA1, in the neuropil of the CA4 region, in polymorphic cells including mossy fiber neurons in the hilus, and dentate gyrus (DG) granule cells. Mean counts of KA1 positive DG granule cells, hippocampal CA3 pyramidal cells, and layer 1 of the frontal cortex were significantly increased in subjects with the deletion allele (P = 0.0005, 0.018, and 0.0058, respectively) compared to subjects homozygous for the insertion. Neuronal expression levels in all regions quantified were higher in the deletion group. These results support our hypothesis that the deletion allele affords protection against bipolar disorder through increased KA1 protein abundance in neuronal cells. Biological mechanisms which may contribute to this protective effect include KA1 involvement in adult hippocampal neurogenesis, HPA axis activation, or plasticity processes affecting neuronal circuitry.

Clustered coding variants in the glutamate receptor complexes of individuals with schizophrenia and bipolar disorder.

Current models of schizophrenia and bipolar disorder implicate multiple genes, however their biological relationships remain elusive. To test the genetic role of glutamate receptors and their interacting scaffold proteins, the exons of ten glutamatergic 'hub' genes in 1304 individuals were re-sequenced in case and control samples. No significant difference in the overall number of non-synonymous single nucleotide polymorphisms (nsSNPs) was observed between cases and controls. However, cluster analysis of nsSNPs identified two exons encoding the cysteine-rich domain and first transmembrane helix of GRM1 as a risk locus with five mutations highly enriched within these domains. A new splice variant lacking the transmembrane GPCR domain of GRM1 was discovered in the human brain and the GRM1 mutation cluster could perturb the regulation of this variant. The predicted effect on individuals harbouring multiple mutations distributed in their ten hub genes was also examined. Diseased individuals possessed an increased load of deleteriousness from multiple concurrent rare and common coding variants. Together, these data suggest a disease model in which the interplay of compound genetic coding variants, distributed among glutamate receptors and their interacting proteins, contribute to the pathogenesis of schizophrenia and bipolar disorders.

A novel balanced chromosomal translocation found in subjects with schizophrenia and schizotypal personality disorder: altered l-serine level associated with disruption of PSAT1 gene expression.

l-Serine is required for the synthesis of glycine and d-serine, both of which are NMDA receptor co-agonists. Although roles for d-serine and glycine have been suggested in schizophrenia, little is known about the role of the l-serine synthesizing cascade in schizophrenia or related psychiatric conditions. Here we report a patient with schizophrenia carrying a balanced chromosomal translocation with the breakpoints localized to 3q13.12 and 9q21.2. We examined this proband and her son with schizotypal personality disorder for chromosomal abnormalities, molecular expression profiles, and serum amino acids. Marked decrease of l-serine and glutamate was observed in the sera of the patient and her son, compared with those in normal controls. Interestingly, expression of PSAT1 gene, which is located next to the breakpoint and encodes one of the enzymes in the l-serine synthesizing cascade, was reduced in both patient and her son. Direct effect of impaired PSAT1 gene expression on decreased serum l-serine level was strongly implicated by rat astrocyte experiments. In summary, we propose an idea that PSAT1 may be implicated in altered serine metabolism and schizophrenia spectrum conditions.

European collaborative study of early-onset bipolar disorder: Evidence for genetic heterogeneity on 2q14 according to age at onset.

Bipolar disorder has a genetic component, but the mode of inheritance remains unclear. A previous genome scan conducted in 70 European families led to detect eight regions linked to bipolar disease. Here, we present an investigation of whether the phenotypic heterogeneity of the disorder corresponds to genetic heterogeneity in these regions using additional markers and an extended sample of families. The MLS statistic was used for linkage analyses. The predivided sample test and the maximum likelihood binomial methods were used to test genetic homogeneity between early-onset bipolar type I (cut-off of 22 years) and other types of the disorder (later onset of bipolar type I and early-onset bipolar type II), using a total of 138 independent bipolar-affected sib-pairs. Analysis of the extended sample of families supports linkage in four regions (2q14, 3p14, 16p23, and 20p12) of the eight regions of linkage suggested by our previous genome scan. Heterogeneity testing revealed genetic heterogeneity between early and late-onset bipolar type I in the 2q14 region (P = 0.0001). Only the early form of the bipolar disorder but not the late form appeared to be linked to this region. This region may therefore include a genetic factor either specifically involved in the early-onset bipolar type I or only influencing the age at onset (AAO). Our findings illustrate that stratification according to AAO may be valuable for the identification of genetic vulnerability polymorphisms. © 2010 Wiley-Liss, Inc.

Association analysis of Neuregulin 1 candidate regions in schizophrenia and bipolar disorder.

Schizophrenia (SCZ) and bipolar disorder (BPD) are severe heritable psychiatric disorders involving a complex genetic aetiology. Neuregulin 1 (NRG1) is a leading candidate gene for SCZ, and has recently been implicated in BPD. We previously reported association of two NRG1 haplotypes with SCZ and BPD in a Scottish case-control sample. One haplotype is located at the 5' end of the gene (region A), and the other is located at the 3' end (region B). Here, association to haplotypes within regions A and B was assessed in patients with SCZ and BPD in a second Scottish case-control sample and in the two Scottish samples combined. Association to region B was also assessed in patients with SCZ and BPD in a German case-control sample, and in all three samples combined. No evidence was found for association in the new samples when analysed individually; however, in the joint analysis of the two Scottish samples, a region B haplotype comprising two SNPs (rs6988339 and rs3757930) was associated with SCZ and the combined case group (SCZ: p=0.0037, OR=1.3, 95% CI: 1.1-1.6; BPD+SCZ: p=0.0080, OR=1.2, 95% CI: 1.1-1.5), with these associations withstanding multiple testing correction at the single-test level (SCZ: p(st)=0.022; BPD+SCZ: p(st)=0.044). This study supports the involvement of NRG1 variants in the less well studied 3' region in conferring susceptibility to SCZ and BPD in the Scottish population.

Support for a bipolar affective disorder susceptibility locus on chromosome 12q24.3.

OBJECTIVE: Linkage and association studies of bipolar affective disorder (BAD) point out chromosome 12q24 as a region of interest. METHODS: To investigate this region further, we conducted an association study of 22 DNA markers within a 1.14 Mb region in a Danish sample of 166 patients with BAD and 311 control individuals. Two-hundred and four Danish patients with schizophrenia were also included in the study. RESULTS: We observed highly significant allelic and genotypic association between BAD and two highly correlated markers. The risk allele of both markers considered separately conferred an odds ratio of 2 to an individual carrying one risk allele and an odds ratio of 4 for individuals carrying both risk alleles assuming an additive genetic model. These findings were supported by the haplotype analysis. In addition, we obtained a replication of four markers associated with BAD in an earlier UK study. The most significantly associated marker was also analyzed in a Scottish case-control sample and was earlier associated with BAD in the UK cohort. The association of that particular marker was strongly associated with BAD in a meta-analysis of the Danish, Scottish and UK sample (P=0.0003). The chromosome region confined by our most distant markers is gene-poor and harbours only a few predicted genes. This study implicates the Slynar locus. We confirmed one annotated Slynar transcript and identified a novel transcript in human brain cDNA. CONCLUSION: This study confirms 12q24.3 as a region of functional importance in the pathogenesis of BAD and highlights the importance of focused genotyping.

Association of GPR50, an X-linked orphan G protein-coupled receptor, and affective disorder in an independent sample of the Scottish population.

A recent report detected association between GPR50, an orphan G protein-coupled receptor, and bipolar disorder (BD) in the Scottish population [29]. We sought to replicate this study in a second sample from the same population, consisting of 338 patients with BD, 359 patients with major depressive disorder (MDD) and 913 control individuals. In addition, the effect of GPR50 genotype on clinical phenotype and treatment response was assessed in a subset of 56 patients with early onset MDD (eoMDD). We identified an association with BD in women with an intronic SNP, rs1202874, that withstood correction for multiple testing (p=0.0035, permuted p=0.037, OR=1.9, 95%CI 1.2-3.0). However, we failed to find an association with the previously associated Delta502-505 polymorphism (p=0.2). Combined analysis of this and the original samples did detect association between the deletion and susceptibility to BD in females, but with a reduced effect size (p=0.0006, permuted p=0.0024, OR=1.41, 95%CI 1.16-1.71). In the highly phenotyped eoMDD subgroup, we found an association between the Delta502-505 deletion polymorphism and age of onset (p=0.049), number of episodes (p=0.044), hypomanic symptoms (p=0.019), and initial thinking time (p=0.027), in women; and in family history of depression in men (p=0.038), uncorrected for multiple testing. No association was seen between Delta502-505 genotype and treatment response at 3 months. To our knowledge this is the first association of rs1202874 with BD and is the second positive association at the GPR50 locus.

Confirmed rare copy number variants implicate novel genes in schizophrenia.

Understanding how cognitive processes including learning, memory, decision making and ideation are encoded by the genome is a key question in biology. Identification of sets of genes underlying human mental disorders is a path towards this objective. Schizophrenia is a common disease with cognitive symptoms, high heritability and complex genetics. We have identified genes involved with schizophrenia by measuring differences in DNA copy number across the entire genome in 91 schizophrenia cases and 92 controls in the Scottish population. Our data reproduce rare and common variants observed in public domain data from >3000 schizophrenia cases, confirming known disease loci as well as identifying novel loci. We found copy number variants in PDE10A (phosphodiesterase 10A), CYFIP1 [cytoplasmic FMR1 (Fragile X mental retardation 1)-interacting protein 1], K(+) channel genes KCNE1 and KCNE2, the Down's syndrome critical region 1 gene RCAN1 (regulator of calcineurin 1), cell-recognition protein CHL1 (cell adhesion molecule with homology with L1CAM), the transcription factor SP4 (specificity protein 4) and histone deacetylase HDAC9, among others (see http://www.genes2cognition.org/SCZ-CNV). Integrating the function of these many genes into a coherent model of schizophrenia and cognition is a major unanswered challenge.

A cytogenetic abnormality and rare coding variants identify ABCA13 as a candidate gene in schizophrenia, bipolar disorder, and depression.

Schizophrenia and bipolar disorder are leading causes of morbidity across all populations, with heritability estimates of approximately 80% indicating a substantial genetic component. Population genetics and genome-wide association studies suggest an overlap of genetic risk factors between these illnesses but it is unclear how this genetic component is divided between common gene polymorphisms, rare genomic copy number variants, and rare gene sequence mutations. We report evidence that the lipid transporter gene ABCA13 is a susceptibility factor for both schizophrenia and bipolar disorder. After the initial discovery of its disruption by a chromosome abnormality in a person with schizophrenia, we resequenced ABCA13 exons in 100 cases with schizophrenia and 100 controls. Multiple rare coding variants were identified including one nonsense and nine missense mutations and compound heterozygosity/homozygosity in six cases. Variants were genotyped in additional schizophrenia, bipolar, depression (n > 1600), and control (n > 950) cohorts and the frequency of all rare variants combined was greater than controls in schizophrenia (OR = 1.93, p = 0.0057) and bipolar disorder (OR = 2.71, p = 0.00007). The population attributable risk of these mutations was 2.2% for schizophrenia and 4.0% for bipolar disorder. In a study of 21 families of mutation carriers, we genotyped affected and unaffected relatives and found significant linkage (LOD = 4.3) of rare variants with a phenotype including schizophrenia, bipolar disorder, and major depression. These data identify a candidate gene, highlight the genetic overlap between schizophrenia, bipolar disorder, and depression, and suggest that rare coding variants may contribute significantly to risk of these disorders.

A case-control association study and family-based expression analysis of the bipolar disorder candidate gene PI4K2B.

Bipolar disorder, schizophrenia and recurrent major depression are complex psychiatric illnesses with a substantial, yet unknown genetic component. Linkage of bipolar disorder and recurrent major depression with markers on chromosome 4p15-p16 has been identified in a large Scottish family and three smaller families. Analysis of haplotypes in the four chromosome 4p-linked families, identified two regions, each shared by three of the four families, which are also supported by a case-control association study. The candidate gene phosphatidylinositol 4-kinase type-II beta (PI4K2B) lies within one of these regions. PI4K2B is a strong functional candidate as it is a member of the phosphatidylinositol pathway, which is targeted by lithium for therapeutic effect in bipolar disorder. Two approaches were undertaken to test the PI4K2B candidate gene as a susceptibility factor for psychiatric illness. First, a case-control association study, using tagging SNPs from the PI4K2B genomic region, in bipolar disorder (n=368), schizophrenia (n=386) and controls (n=458) showed association with a two-marker haplotype in schizophrenia but not bipolar disorder (rs10939038 and rs17408391, global P=0.005, permuted global P=0.039). Second, expression studies at the allele-specific mRNA and protein level using lymphoblastoid cell lines from members of the large Scottish family, which showed linkage to 4p15-p16 in bipolar disorder and recurrent major depression, showed no difference in expression differences between affected and non-affected family members. There is no evidence to suggest that PI4K2B is contributing to bipolar disorder in this family but a role for this gene in schizophrenia has not been excluded.

Can epigenetics help in the discovery of therapeutics for psychiatric disorders, especially schizophrenia?

Psychiatric disorders have a heterogeneous biological basis, where environmental factors interplay with non-mendelian genetics to produce complex cognitive/behavioural syndromes such as schizophrenia. Recent findings indicate a proportion of schizophrenia is associated with genomic copy number variation, suggesting that alteration of gene expression levels rather than direct mutation may play a role. Epigenetic mechanisms could be the crucial link between external stimuli and gene expression, influencing schizophrenia risk. These are dynamic reversible systems that offer much promise as targets for future therapies.

Collaborative genome-wide association analysis supports a role for ANK3 and CACNA1C in bipolar disorder.

To identify susceptibility loci for bipolar disorder, we tested 1.8 million variants in 4,387 cases and 6,209 controls and identified a region of strong association (rs10994336, P = 9.1 x 10(-9)) in ANK3 (ankyrin G). We also found further support for the previously reported CACNA1C (alpha 1C subunit of the L-type voltage-gated calcium channel; combined P = 7.0 x 10(-8), rs1006737). Our results suggest that ion channelopathies may be involved in the pathogenesis of bipolar disorder.

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.

Homozygosity mapping in a family presenting with schizophrenia, epilepsy and hearing impairment.

Homozygosity mapping within consanguineous families is a powerful method of localising genes for autosomal recessive disease. We investigated a family from Punjab, Pakistan, a region where consanguineous marriages are frequent. The parents have no detectable clinical disorders. However, five out of six children present with schizophrenia, epilepsy or hearing impairment either alone or in combination. This unusual phenotype in several offspring of first cousins is strongly suggestive of a rare, Mendelian recessive disorder. Two genome-wide scans initially using low-density microsatellites, and subsequently high-density SNP markers were used to map homozygous-by-descent regions in affected individuals. Candidate genes within these loci were subsequently screened for mutations. Homozygosity analysis and inbreeding coefficients were investigated to give an estimate of consanguinity. Two putative disease loci were mapped to 22q12.3-q13.3 and 2p24.3. The candidate locus on chromosome 2p24 overlaps with a deafness locus, DFNB47, linked to autosomal recessive hearing impairment, while positive findings reported for affective psychosis and schizophrenia cluster in a region of 4-5 cM on 22q13.1 within our second candidate locus. Sequence analysis of three candidate genes (KCNF1 (2p); ATF4, CACNG2 (22q)) did not reveal any exonic mutations. Inbreeding coefficients calculated for each family member support a very high degree of ancestral and recent inbreeding. The screening of other candidate genes located within these newly identified disease intervals on Chr2p24.3 and 22q12.3-q13.3 may lead to the discovery of causative variants, and consequent disrupted molecular pathways associated with this rare phenotype.

Initial association of NR2E1 with bipolar disorder and identification of candidate mutations in bipolar disorder, schizophrenia, and aggression through resequencing.

Nuclear receptor 2E1 gene (NR2E1) resides within a 6q21-22 locus for bipolar disorder and schizophrenia. Mice deleted for Nr2e1 show altered neurogenesis, cortical and limbic abnormalities, aggression, hyperexcitability, and cognitive impairment. NR2E1 is therefore a positional and functional candidate for involvement in mental illness. We performed association analyses in 394 patients with bipolar disorder, 396 with schizophrenia, and 479 controls using six common markers and haplotypes. We also performed a comprehensive mutation screen of NR2E1, resequencing its entire coding region, complete 5' and 3' untranslated regions, consensus splice-sites, and evolutionarily conserved regions in 126 humans with bipolar disorder, schizophrenia, or aggressive disorders. NR2E1 was associated with bipolar disorder I and II [odds ratio (OR = 0.77, P = 0.013), bipolar disorder I (OR = 0.77, P = 0.015), bipolar disorder in females (OR = 0.72, P = 0.009), and with age at onset < or = 25 years (OR = 0.67, P = 0.006)], all of which remained significant after correcting for multiple comparisons. We identified eight novel candidate mutations that were absent in 325 controls; four of these were predicted to alter known neural transcription factor binding sites. Analyses of NR2E1 mRNA in human brain revealed forebrain-specific transcription. The data presented support the hypothesis that genetic variation at NR2E1 may be associated with susceptibility to brain-behavior disorders.

A genome-wide linkage study in families with major depression and co-morbid unexplained swelling.

Major depressive disorder (MDD) is a common heritable condition. The diversity of the phenotype coupled with aetiological and genetic heterogeneity present formidable obstacles in the search for causative genetic loci. Studies of large families with many affected individuals, and the selection of well-defined clinical subgroups of depression, are two ways to reduce this complexity. Unexplained swelling symptoms (USS) are common in women and many patients give a strong personal and family history of depression. Co-morbid depression and swelling symptoms define a useful sub-phenotype for investigating genetic factors in depression. We have completed a genome-wide linkage analysis using 371 microsatellite markers in four families where MDD is co-morbid with USS. Of 47 affected individuals, 28 had both MDD and unexplained swelling, 11 had symptoms of swelling alone, and 8 had MDD alone. Parametric marker-specific analysis identified one suggestive locus, D8S260 (LOD = 2.02) and non-parametric multipoint variance component analysis identified a region on 7p (LOD = 2.10). A 47 cM suggestive linkage region on chromosome 14q (identified by both parametric and non-parametric methods) was identified and investigated further with fine-mapping markers but the evidence for linkage to this region decreased with increased marker information content.

Schizotypal cognitions as a predictor of psychopathology in adolescents with mild intellectual impairment.

BACKGROUND: There is evidence to suggest that among young people with mild intellectual disability there are those whose cognitive difficulties may predict the subsequent manifestation of a schizophrenic phenotype. It is suggested that they may be detectable by simple means. AIMS: To gain adequate cooperation from educational services, parents and students so as to recruit a sufficiently large sample to test the above hypothesis, and to examine the hypothesis in the light of the findings. METHOD: The sample was screened with appropriate instruments, and groups hypothesised as being likely or not likely to have the phenotype were compared in terms of psychopathology and neuropsychology. RESULTS: Simple screening methods detect a sample whose psychopathological and neuropsychological profile is consistent with an extended phenotype of schizophrenia. CONCLUSIONS: Difficulties experienced by some young people with mild and borderline intellectual disability are associated with enhanced liability to schizophrenia. Clinical methods can both identify those with this extended phenotype and predict those in whom psychosis will occur.

Disrupted in schizophrenia 1 and phosphodiesterase 4B: towards an understanding of psychiatric illness.

Disrupted in schizophrenia 1 (DISC1) is one of the most convincing genetic risk factors for major mental illness identified to date. DISC1 interacts directly with phosphodiesterase 4B (PDE4B), an independently identified risk factor for schizophrenia. DISC1-PDE4B complexes are therefore likely to be involved in molecular mechanisms underlying psychiatric illness. PDE4B hydrolyses cAMP and DISC1 may regulate cAMP signalling through modulating PDE4B activity. There is evidence that expression of both genes is altered in some psychiatric patients. Moreover, DISC1 missense mutations that give rise to phenotypes related to schizophrenia and depression in mice are located within binding sites for PDE4B. These mutations reduce the association between DISC1 and PDE4B, and one results in reduced brain PDE4B activity. Altered DISC1-PDE4B interaction may thus underlie the symptoms of some cases of schizophrenia and depression. Factors likely to influence this interaction include expression levels, binding site affinities and the DISC1 and PDE4 isoforms involved. DISC1 and PDE4 isoforms are targeted to specific subcellular locations which may contribute to the compartmentalization of cAMP signalling. Dysregulated cAMP signalling in specific cellular compartments may therefore be a predisposing factor for major mental illness.