Helen S. Torrance

The DISC1 promoter: characterization and regulation by FOXP2

Disrupted in schizophrenia 1 (DISC1) is a leading candidate susceptibility gene for schizophrenia, bipolar disorder and recurrent major depression, which has been implicated in other psychiatric illnesses of neurodevelopmental origin, including autism. DISC1 was initially identified at the breakpoint of a balanced chromosomal translocation, t(1;11) (q42.1;14.3), in a family with a high incidence of psychiatric illness. Carriers of the translocation show a 50% reduction in DISC1 protein levels, suggesting altered DISC1 expression as a pathogenic mechanism in psychiatric illness. Altered DISC1 expression in the post-mortem brains of individuals with psychiatric illness and the frequent implication of non-coding regions of the gene by association analysis further support this assertion. Here, we provide the first characterization of the DISC1 promoter region. Using dual luciferase assays, we demonstrate that a region -300 to -177 bp relative to the transcription start site (TSS) contributes positively to DISC1 promoter activity, while a region -982 to -301 bp relative to the TSS confers a repressive effect. We further demonstrate inhibition of DISC1 promoter activity and protein expression by forkhead-box P2 (FOXP2), a transcription factor implicated in speech and language function. This inhibition is diminished by two distinct FOXP2 point mutations, R553H and R328X, which were previously found in families affected by developmental verbal dyspraxia. Our work identifies an intriguing mechanistic link between neurodevelopmental disorders that have traditionally been viewed as diagnostically distinct but which do share varying degrees of phenotypic overlap.

Haplotype Analysis and a Novel Allele-Sharing Method Refines a Chromosome 4p Locus Linked to Bipolar Affective Disorder

BACKGROUND Bipolar affective disorder (BPAD) and schizophrenia (SCZ) are common conditions. Their causes are unknown, but they include a substantial genetic component. Previously, we described significant linkage of BPAD to a chromosome 4p locus within a large pedigree (F22). Others subsequently have found evidence for linkage of BPAD and SCZ to this region. METHODS We constructed high-resolution haplotypes for four linked families, calculated logarithm of the odds (LOD) scores, and developed a novel method to assess the extent of allele sharing within genes between the families. RESULTS We describe an increase in the F22 LOD score for this region. Definition and comparison of the linked haplotypes allowed us to prioritize two subregions of 3.8 and 4.4 Mb. Analysis of the extent of allele sharing within these subregions identified 200 kb that shows increased allele sharing between families. CONCLUSIONS Linkage of BPAD to chromosome 4p has been strengthened. Haplotype analysis in the additional linked families refined the 20-Mb linkage region. Development of a novel allele-sharing method allowed us to bridge the gap between conventional linkage and association studies. Description of a 200-kb region of increased allele sharing prioritizes this region, which contains two functional candidate genes for BPAD, SLC2A9, and WDR1, for subsequent studies.

Convergence of linkage, association and GWAS findings for a candidate region for bipolar disorder and schizophrenia on chromosome 4p

Convergence of linkage, association and GWAS findings for a candidate region for bipolar disorder and schizophrenia on chromosome 4p

Synaptic modulators Nrxn1 and Nrxn3 are disregulated in a Disc1 mouse model of schizophrenia

Synaptic modulators Nrxn1 and Nrxn3 are disregulated in a Disc1 mouse model of schizophrenia

Juvenile stress produces long-lasting changes in hippocampal DISC1, GSK3ß and NRG1 expression

Juvenile stress produces long-lasting changes in hippocampal DISC1, GSK3s and NRG1 expression

Expression of DISC1-Interactome Members Correlates with Cognitive Phenotypes Related to Schizophrenia

Cognitive dysfunction is central to the schizophrenia phenotype. Genetic and functional studies have implicated Disrupted-in-Schizophrenia 1 (DISC1), a leading candidate gene for schizophrenia and related psychiatric conditions, in cognitive function. Altered expression of DISC1 and DISC1-interactors has been identified in schizophrenia. Dysregulated expression of DISC1-interactome genes might, therefore, contribute to schizophrenia susceptibility via disruption of molecular systems required for normal cognitive function. Here, the blood RNA expression levels of DISC1 and DISC1-interacting proteins were measured in 63 control subjects. Cognitive function was assessed using neuropsychiatric tests and functional magnetic resonance imaging was used to assess the activity of prefrontal cortical regions during the N-back working memory task, which is abnormal in schizophrenia. Pairwise correlations between gene expression levels and the relationship between gene expression levels and cognitive function and N-back-elicited brain activity were assessed. Finally, the expression levels of DISC1, AKAP9, FEZ1, NDEL1 and PCM1 were compared between 63 controls and 69 schizophrenic subjects. We found that DISC1-interactome genes showed correlated expression in the blood of healthy individuals. The expression levels of several interactome members were correlated with cognitive performance and N-back-elicited activity in the prefrontal cortex. In addition, DISC1 and NDEL1 showed decreased expression in schizophrenic subjects compared to healthy controls. Our findings highlight the importance of the coordinated expression of DISC1-interactome genes for normal cognitive function and suggest that dysregulated DISC1 and NDEL1 expression might, in part, contribute to susceptibility for schizophrenia via disruption of prefrontal cortex-dependent cognitive functions.

Preliminary investigation of miRNA expression in individuals at high familial risk of bipolar disorder

Bipolar disorder (BD) is a highly heritable psychiatric disorder characterised by recurrent episodes of mania and depression. Many studies have reported altered gene expression in BD, some of which may be attributable to the dysregulated expression of miRNAs. Studies carried out to date have largely studied medicated patients, so it is possible that observed changes in miRNA expression might be a consequence of clinical illness or of its treatment. We sought to establish whether altered miRNA expression might play a causative role in the development of BD by studying young, unmedicated relatives of individuals with BD, who are at a higher genetic risk of developing BD themselves (high-risk individuals). The expression of 20 miRNAs previously implicated in either BD or schizophrenia was measured by qRT-PCR in whole-blood samples from 34 high-risk and 46 control individuals. Three miRNAs, miR-15b, miR-132 and miR-652 were up-regulated in the high-risk individuals, consistent with previous reports of increased expression of these miRNAs in patients with schizophrenia. Our findings suggest that the altered expression of these miRNAs might represent a mechanism of genetic susceptibility for BD. Moreover, our observation of altered miRNA expression in the blood prior to the onset of illness provides hope that one day blood-based tests may aid in the risk-stratification and treatment of BD.

NDE1 and GSK3β Associate with TRAK1 and Regulate Axonal Mitochondrial Motility: Identification of Cyclic AMP as a Novel Modulator of Axonal Mitochondrial Trafficking

Mitochondria are essential for neuronal function, providing the energy required to power neurotransmission, and fulfilling many important additional roles. In neurons, mitochondria must be efficiently transported to sites, including synapses, where their functions are required. Neurons, with their highly elongated morphology, are consequently extremely sensitive to defective mitochondrial trafficking which can lead to neuronal ill-health/death. We recently demonstrated that DISC1 associates with mitochondrial trafficking complexes where it associates with the core kinesin and dynein adaptor molecule TRAK1. We now show that the DISC1 interactors NDE1 and GSK3β also associate robustly with TRAK1 and demonstrate that NDE1 promotes retrograde axonal mitochondrial movement. GSK3β is known to modulate axonal mitochondrial motility, although reports of its actual effect are conflicting. We show that, in our system, GSK3β promotes anterograde mitochondrial transport. Finally, we investigated the influence of cAMP elevation upon mitochondrial motility, and found a striking increase in mitochondrial motility and retrograde movement. DISC1, NDE1, and GSK3β are implicated as risk factors for major mental illness. Our demonstration that they function together within mitochondrial trafficking complexes suggests that defective mitochondrial transport may be a contributory disease mechanism in some cases of psychiatric disorder.

DNA methylation in a Scottish family multiply affected by bipolar disorder and major depressive disorder

BackgroundBipolar disorder (BD) is a severe, familial psychiatric condition. Progress in understanding the aetiology of BD has been hampered by substantial phenotypic and genetic heterogeneity. We sought to mitigate these confounders by studying a multi-generational family multiply affected by BD and major depressive disorder (MDD), who carry an illness-linked haplotype on chromosome 4p. Within a family, aetiological heterogeneity is likely to be reduced, thus conferring greater power to detect illness-related changes. As accumulating evidence suggests that altered DNA methylation confers risk for BD and MDD, we compared genome-wide methylation between (i) affected carriers of the linked haplotype (ALH) and married-in controls (MIs), (ii) well unaffected haplotype carriers (ULH) and MI, (iii) ALH and ULH and (iv) all haplotype carriers (LH) and MI.ResultsNominally significant differences in DNA methylation were observed in all comparisons, with differences withstanding correction for multiple testing when the ALH or LH group was compared to the MIs. In both comparisons, we observed increased methylation at a locus in FANCI, which was accompanied by increased FANCI expression in the ALH group. FANCI is part of the Fanconi anaemia complementation (FANC) gene family, which are mutated in Fanconi anaemia and participate in DNA repair. Interestingly, several FANC genes have been implicated in psychiatric disorders. Regional analyses of methylation differences identified loci implicated in psychiatric illness by genome-wide association studies, including CACNB2 and the major histocompatibility complex. Gene ontology analysis revealed enrichment for methylation differences in neurologically relevant genes.ConclusionsOur results highlight altered DNA methylation as a potential mechanism by which the linked haplotype might confer risk for mood disorders. Differences in the phenotypic outcome of haplotype carriers might, in part, arise from additional changes in DNA methylation that converge on neurologically important pathways. Further work is required to investigate the underlying mechanisms and functional consequences of the observed differences in methylation.

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.