Chromosome 1 loci in Finnish schizophrenia families

The associations between cognitive functions and TSNAX genetic variations in patients with schizophrenia

BACKGROUND

The translin-associated factor X (TSNAX) gene, located adjacent to the DISC1 gene, has been implicated in schizophrenia. While cognitive impairment determines long-term the functional outcome of schizophrenia, the role of TSNAX in cognitive dysfunction of schizophrenia patients remains elusive. This study aimed to explore the genetic effect of TSNAX on cognitive functions of schizophrenia.

METHODS

We recruited 286 chronic schizophrenia patients who had been stabilized with antipsychotics for at least 2 months and genotyped three TSNAX SNPs (rs1630250, rs766288, rs6662926). Clinical symptoms and seven cognitive domains were assessed. The score of cognitive tests was standardized to T score.

RESULTS

Clinical symptoms were similar among genotypes of all the three SNPs. The GLM analysis demonstrated that TSNAX genetic polymorphisms influenced cognitive function of schizophrenia patients after adjustment for gender, age, and education. The patients with the rs1630250 C/G genotype performed better than the G/G homozygotes in the Trail Making A (p = 0.034). Those with the rs766288 G/T genotype also performed better than the G/G homozygotes in the Trail Making A (p = 0.012). The patients with the G/G genotype of rs6662926 also performed better than the C/C homozygotes in verbal learning and memory test (p = 0.044).

CONCLUSIONS

This study suggests that the TSNAX gene variation may influence the cognitive functions of the patients with schizophrenia.

Gene expression meta-analysis in patients with schizophrenia reveals up-regulation of RGS2 and RGS16 in Brodmann Area 10

Regulator of G-protein signalling (RGS) proteins inhibit signalling by G-protein-coupled receptors (GPCRs). GPCRs mediate the functions of several important neurotransmitters and serve as targets of many anti-psychotics. RGS2, RGS4, RGS5 and RGS16 are located on chromosome 1q23.3-31, a locus found to be associated with schizophrenia. Although previous gene expression analysis detected down-regulation of RGS4 expression in brain samples of patients with schizophrenia, the results were not consistent. In the present study, we performed a systematic meta-analysis of differential RGS2, RGS4, RGS5 and RGS16 expression in Brodmann Area 10 (BA10) samples of patients with schizophrenia and from healthy controls. Two microarray datasets met the inclusion criteria (overall, 41 schizophrenia samples and 38 controls were analysed). RGS2 and RGS16 were found to be up-regulated in BA10 samples of individuals with schizophrenia, whereas no differential expression of RGS4 and RGS5 was detected. Analysis of dorso-lateral prefrontal cortex samples of the CommonMind Consortium (258 schizophrenia samples vs. 279 controls) further validated the results. Given their central role in inactivating G-protein-coupled signalling pathways, our results suggest that differential gene expression might lead to enhanced inactivation of G-protein signalling in schizophrenia. This, in turn, suggests that additional studies are needed to further explore the consequences of the differential expression we detected, this time at the protein and functional levels.

Mutations in DISC1 alter IP3R and voltage-gated Ca2+ channel functioning, implications for major mental illness

Disrupted in Schizophrenia 1 (DISC1) participates in a wide variety of developmental processes of central neurons. It also serves critical roles that underlie cognitive functioning in adult central neurons. Here we summarize DISC1’s general properties and discuss its use as a model system for understanding major mental illnesses (MMIs). We then discuss the cellular actions of DISC1 that involve or regulate Ca²⁺ signaling in adult central neurons. In particular, we focus on the tethering role DISC1 plays in transporting RNA particles containing Ca²⁺ channel subunit RNAs, including IP3R1, CACNA1C and CACNA2D1, and in transporting mitochondria into dendritic and axonal processes. We also review DISC1’s role in modulating IP₃R1 activity within mitochondria-associated ER membrane (MAM). Finally, we discuss DISC1-glycogen synthase kinase 3β (GSK3β) signaling that regulates functional expression of voltage-gated Ca²⁺ channels (VGCCs) at central synapses. In each case, DISC1 regulates the movement of molecules that impact Ca²⁺ signaling in neurons.

Kynurenine pathway in Parkinson's disease-An update

Parkinson's disease (PD) is a complex multi-factorial neurodegenerative disorder where various altered metabolic pathways contribute to the progression of the disease. Tryptophan (TRP) is a major precursor in kynurenine pathway (KP) and it has been discussed in various in vitro studies that the metabolites quinolinic acid (QUIN) causes neurotoxicity and kynurenic acid (KYNA) acts as neuroprotectant respectively. More studies are also focused on the effects of other KP metabolites and its enzymes as it has an association with ageing and PD pathogenesis. Until now, very few studies have targeted the role of genetic mutations in abnormal KP metabolism in adverse conditions of PD. Therefore, the present review gives an updated research studies on KP in connection with PD. Moreover, the review emphasizes on the urge for the development of biomarkers and also this would be an initiative in generating an alternative therapeutic approach for PD.

Evidence of association of the DISC1 interactome gene set with schizophrenia from GWAS

DISC1 was discovered as a gene disrupted by a balanced translocation in a large pedigree that segregated with major mental disorders, including schizophrenia. Further attempts to find genetic association with schizophrenia were inconclusive. Most of the biology of DISC1 was inferred from the functionality of its protein partners. Recently, a gene set constituted by DISC1 and several of its partners has been associated with cognitive performance during development, a well-known schizophrenia endophenotype, by means of burden test of rare disruptive variants. Here, we performed a gene set analysis using common variants from the largest schizophrenia genome-wide association study of the Psychiatric Genomics Consortium to test if this gene set is associated with schizophrenia. The main test was based on the MAGMA software. Several additional tests were performed to analyze the robustness of the main findings. The DISC1 interactome gene set was associated with schizophrenia (P = .0056), confirmed by an additional method (INRICH). This association was robust to removal of the major histocompatibility complex region, different definitions of gene boundaries, or different statistical gene models. Conditional analysis revealed that the association was not solely explained by higher expression in brain. Three genes from the gene set, CLIC1, DST, and PDE4B, were associated with schizophrenia at the gene level. Consideration of other DISC1 interactome gene sets revealed the importance of gene set definition. Therefore, we present the first evidence from genome-wide association studies of the role of DISC1 and interacting partners in schizophrenia susceptibility, reconciling genetic and molecular biology data.

Disrupted-in-schizophrenia 1 functional polymorphisms and D2 /D3 receptor availability: A [11 C]-(+)-PHNO imaging study

The disrupted-in-schizophrenia 1 (DISC1) protein has been implicated in a range of biological mechanisms underlying chronic mental disorders such as schizophrenia. Schizophrenia is associated with abnormal striatal dopamine signalling, and all antipsychotic drugs block striatal dopamine 2/3 receptors (D_2/3 Rs). Importantly, the DISC1 protein directly interacts and forms a protein complex with the dopamine D₂ receptor (D₂ R) that inhibits agonist-induced D₂ R internalisation. Moreover, animal studies have found large striatal increases in the proportion of D₂ R receptors in a high affinity state (D₂ ^high R) in DISC1 rodent models. Here, we investigated the relationship between the three most common polymorphisms altering the amino-acid sequence of the DISC1 protein (Ser704Cys (rs821616), Leu607Phe (rs6675281) and Arg264Gln (rs3738401)) and striatal D_2/3 R availability in 41 healthy human volunteers, using [¹¹ C]-(+)-PHNO positron emission tomography. We found no association between DISC1 polymorphisms and D_2/3 R availability in the striatum and D₂ R availability in the caudate and putamen. Therefore, despite a direct interaction between DISC1 and the D₂ R, none of its main functional polymorphisms impact striatal D_2/3 R binding potential, suggesting DISC1 variants act through other mechanisms.

Dysregulation of a specific immune-related network of genes biologically defines a subset of schizophrenia

Currently, the clinical diagnosis of schizophrenia relies solely on self-reporting and clinical interview, and likely comprises heterogeneous biological subsets. Such subsets may be defined by an underlying biology leading to solid biomarkers. A transgenic rat model modestly overexpressing the full-length, non-mutant Disrupted-in-Schizophrenia 1 (DISC1) protein (tgDISC1 rat) was generated that defines such a subset, inspired by our previous identification of insoluble DISC1 protein in post mortem brains from patients with chronic mental illness. Besides specific phenotypes such as DISC1 protein pathology, abnormal dopamine homeostasis, and changes in neuroanatomy and behavior, this animal model also shows subtle disturbances in overarching signaling pathways relevant for schizophrenia. In a reverse-translational approach, assuming that both the animal model and a patient subset share common disturbed signaling pathways, we identified differentially expressed transcripts from peripheral blood mononuclear cells of tgDISC1 rats that revealed an interconnected set of dysregulated genes, led by decreased expression of regulator of G-protein signaling 1 (RGS1), chemokine (C-C) ligand 4 (CCL4), and other immune-related transcripts enriched in T-cell and macrophage signaling and converging in one module after weighted gene correlation network analysis. Testing expression of this gene network in two independent cohorts of patients with schizophrenia versus healthy controls (n = 16/50 and n = 54/45) demonstrated similar expression changes. The two top markers RGS1 and CCL4 defined a subset of 27% of patients with 97% specificity. Thus, analogous aberrant signaling pathways can be identified by a blood test in an animal model and a corresponding schizophrenia patient subset, suggesting that in this animal model tailored pharmacotherapies for this patient subset could be achieved.

Genetic associations and expression of extra-short isoforms of disrupted-in-schizophrenia 1 in a neurocognitive subgroup of schizophrenia

Disrupted-in-schizophrenia 1 (DISC1) was reported to be associated with schizophrenia. In a previous study, we found significant association with schizophrenia patients with deficient sustained attention assessed by continuous performance test (CPT). This study aimed to identify risk polymorphisms in this specific neurocognitive subgroup and investigate the expression of different isoforms of DISC1. A total of 83 genetic variants were identified through direct sequencing in 50 controls and 100 schizophrenia patients. Fourteen variants were genotyped in 600 controls and 912 patients. Patients were subgrouped by familial loading (multiplex or simplex) and performance on CPT. The frequency of AA genotype of rs11122324 at the 3'-UTR of Es and Esv1 isoforms and of rs2793091 at intron 4 were significantly higher in multiplex schizophrenia patients than those in controls (corrected p < 0.05). In further subgrouping, the frequency of AA genotype of the two SNPs were significantly higher in multiplex schizophrenia patients with deficient sustained attention than those in controls (corrected p < 0.005). The mRNA expression levels of two extra-short isoforms (Es and Esv1) in the EBV-transformed lymphocytes of schizophrenia were significantly higher than those of controls. Luciferase reporter assays demonstrated that the A-allele of rs11122324 significantly upregulated DISC1 extra-short isoforms transcription compared with the G-allele. We found two SNPs (rs11122324 and rs2793091) of DISC1 may be specifically associated with multiplex schizophrenia patients with deficient sustained attention. The SNP rs11122324 may be a risk polymorphism, which may have functional influence on the transcription of Es and Esv1 through increasing their expression.

Application of Human-Induced Pluripotent Stem Cells (hiPSCs) to Study Synaptopathy of Neurodevelopmental Disorders

Synapses are the basic structural and functional units for information processing and storage in the brain. Their diverse properties and functions ultimately underlie the complexity of human behavior. Proper development and maintenance of synapses are essential for normal functioning of the nervous system. Disruption in synaptogenesis and the consequent alteration in synaptic function have been strongly implicated to cause neurodevelopmental disorders such as autism spectrum disorders (ASDs) and schizophrenia (SCZ). The introduction of human-induced pluripotent stem cells (hiPSCs) provides a new path to elucidate disease mechanisms and potential therapies. In this review, we will discuss the advantages and limitations of using hiPSC-derived neurons to study synaptic disorders. Many mutations in genes encoding for proteins that regulate synaptogenesis have been identified in patients with ASDs and SCZ. We use Methyl-CpG binding protein 2 (MECP2), SH3 and multiple ankyrin repeat domains 3 (SHANK3) and Disrupted in schizophrenia 1 (DISC1) as examples to illustrate the promise of using hiPSCs as cellular models to elucidate the mechanisms underlying disease-related synaptopathy.

The effect of the DISC1 Ser704Cys polymorphism on striatal dopamine synthesis capacity: an [18F]-DOPA PET study

Whilst the role of the Disrupted-in-Schizophrenia 1 (DISC1) gene in the aetiology of major mental illnesses is debated, the characterization of its function lends it credibility as a candidate. A key aspect of this functional characterization is the determination of the role of common non-synonymous polymorphisms on normal variation within these functions. The common allele (A) of the DISC1 single-nucleotide polymorphism (SNP) rs821616 encodes a serine (ser) at the Ser704Cys polymorphism, and has been shown to increase the phosphorylation of extracellular signal-regulated protein Kinases 1 and 2 (ERK1/2) that stimulate the phosphorylation of tyrosine hydroxylase, the rate-limiting enzyme for dopamine biosynthesis. We therefore set out to test the hypothesis that human ser (A) homozygotes would show elevated dopamine synthesis capacity compared with cysteine (cys) homozygotes and heterozygotes (TT and AT) for rs821616. [18F]-DOPA positron emission tomography (PET) was used to index striatal dopamine synthesis capacity as the influx rate constant Kicer in healthy volunteers DISC1 rs821616 ser homozygotes (N = 46) and healthy volunteers DISC1 rs821616 cys homozygotes and heterozygotes (N = 56), matched for age, gender, ethnicity and using three scanners. We found DISC1 rs821616 ser homozygotes exhibited a significantly higher striatal Kicer compared with cys homozygotes and heterozygotes (P = 0.012) explaining 6.4% of the variance (partial η2 = 0.064). Our finding is consistent with its previous association with heightened activation of ERK1/2, which stimulates tyrosine hydroxylase activity for dopamine synthesis. This could be a potential mechanism mediating risk for psychosis, lending further credibility to the fact that DISC1 is of functional interest in the aetiology of major mental illness.

Genetic alterations affecting the genes encoding the enzymes of the kynurenine pathway and their association with human diseases

Tryptophan is metabolized primarily via the kynurenine pathway (KP), which involves several enzymes, including indoleamine 2,3-dioxygenase, tryptophan 2,3 dioxygenase (TDO), kynurenine aminotransferases (KATs), kynurenine monooxygenase (KMO) etc. The majority of metabolites are neuroactive: some of them, such as kynurenic acid, show neuroprotective effects, while others contribute to free radical production, leading to neurodegeneration. Imbalance of the pathway is assumed to contribute to the development of several neurodegenerative diseases, psychiatric disorders, migraine and multiple sclerosis. Our aim was to summarize published data on genetic alterations of enzymes involved in the KP leading to disturbances of the pathway that can be related to different diseases. To achieve this, a PubMed literature search was performed for publications on genetic alterations of the KP enzymes upto April 2017. Several genetic alterations of the KP have been identified and have been proposed to be associated with diseases. Here we must emphasize that despite the large number of recognized genetic alterations, the number of firmly established causal relations with specific diseases is still small. The realization of this by those interested in the field is very important and finding such connections should be a major focus of related research. Polymorphisms of the genes encoding the enzymes of the KP have been associated with autism, multiple sclerosis and schizophrenia, and were shown to affect the immune response of patients with bacterial meningitis, just to mention a few. To our knowledge, this is the first comprehensive review of the genetic alterations of the KP enzymes. We believe that the identification of genetic alterations underlying diseases has great value regarding both treatment and diagnostics in precision medicine, as this work can promote the understanding of pathological mechanisms, and might facilitate medicinal chemistry approaches to substitute missing components or correct the disturbed metabolite balance of KP.

A Gene-Based Analysis of Acoustic Startle Latency

Latency of the acoustic startle response is the time required from the presentation of startling auditory stimulus until the startle response is elicited and provides an index of neural processing speed. Latency is prolonged in subjects with schizophrenia compared to controls in some but not all studies and is 68-90% heritable in baseline startle trials. In order to determine the genetic association with latency as a potential inroad into genetically based vulnerability to psychosis, we conducted a gene-based study of latency followed by an independent replication study of significant gene findings with a single-nucleotide polymorphism (SNP)-based analysis of schizophrenia and control subjects. 313 subjects from an urban population of low socioeconomic status with mixed psychiatric diagnoses were included in the gene-based study. Startle testing was conducted using a Biopac M150 system according to our published methods. Genotyping was performed with the Omni-Quad 1M or the Omni Express BeadChip. The replication study was conducted on 154 schizophrenia subjects and 123 psychiatric controls. Genetic analyses were conducted with Illumina Human Omni1-Quad and OmniExpress BeadChips. Twenty-nine SNPs were selected from four genes that were significant in the gene-based analysis and also associated with startle and/or schizophrenia in the literature. Linear regressions on latency were conducted, controlling for age, race, and diagnosis as a dichotomous variable. In the gene-based study, 2,870 genes demonstrated the evidence of association after correction for multiple comparisons (false discovery rate < 0.05). Pathway analysis of these genes revealed enrichment for relevant biological processes including neural transmission (p = 0.0029), synaptic transmission (p = 0.0032), and neuronal development (p = 0.024). The subsequent SNP-based replication analysis revealed a strong association of onset latency with the SNP rs901561 on the neuregulin gene (NRG1) in an additive model (beta = 0.21, p = 0.001), indicating that subjects with the AA and AG genotypes had slower mean latency than subjects with GG genotype. In conclusion, startle latency, a highly heritable measure that is slowed in schizophrenia, may be a useful biological probe for genetic contributions to psychotic disorders. Our analyses in two independent populations point to a significant prediction of startle latency by genetic variation in NRG1.

Caveolin-1 regulation of disrupted-in-schizophrenia-1 as a potential therapeutic target for schizophrenia

Schizophrenia is a debilitating psychiatric disorder manifested in early adulthood. Disrupted-in-schizophrenia-1 (DISC1) is a susceptible gene for schizophrenia (Hodgkinson et al. 2004; Millar et al. 2000; St Clair et al. 1990) implicated in neuronal development, brain maturation, and neuroplasticity (Brandon and Sawa 2011; Chubb et al. 2008). Therefore, DISC1 is a promising candidate gene for schizophrenia, but the molecular mechanisms underlying its role in the pathogenesis of the disease are still poorly understood. Interestingly, caveolin-1 (Cav-1), a cholesterol binding and scaffolding protein, regulates neuronal signal transduction and promotes neuroplasticity. In this study we examined the role of Cav-1 in mediating DISC1 expression in neurons in vitro and the hippocampus in vivo. Overexpressing Cav-1 specifically in neurons using a neuron-specific synapsin promoter (SynCav1) increased expression of DISC1 and proteins involved in synaptic plasticity (PSD95, synaptobrevin, synaptophysin, neurexin, and syntaxin 1). Similarly, SynCav1-transfected differentiated human neurons derived from induced pluripotent stem cells (hiPSCs) exhibited increased expression of DISC1 and markers of synaptic plasticity. Conversely, hippocampi from Cav-1 knockout (KO) exhibited decreased expression of DISC1 and proteins involved in synaptic plasticity. Finally, SynCav1 delivery to the hippocampus of Cav-1 KO mice and Cav-1 KO neurons in culture restored expression of DISC1 and markers of synaptic plasticity. Furthermore, we found that Cav-1 coimmunoprecipitated with DISC1 in brain tissue. These findings suggest an important role by which neuron-targeted Cav-1 regulates DISC1 neurobiology with implications for synaptic plasticity. Therefore, SynCav1 might be a potential therapeutic target for restoring neuronal function in schizophrenia.

NEW & NOTEWORTHY

The present study is the first to demonstrate that caveolin-1 can regulate DISC1 expression in neuronal models. Furthermore, the findings are consistent across three separate neuronal models that include rodent neurons (in vitro and in vivo) and human differentiated neurons derived from induced pluripotent stem cells. These findings justify further investigation regarding the modulatory role by caveolin on synaptic function and as a potential therapeutic target for the treatment of schizophrenia.

Adult neurogenesis and neurodegenerative diseases: A systems biology perspective

New neurons are generated throughout adulthood in two regions of the brain, the olfactory bulb and dentate gyrus of the hippocampus, and are incorporated into the hippocampal network circuitry; disruption of this process has been postulated to contribute to neurodegenerative diseases including Alzheimer's disease and Parkinson's disease. Known modulators of adult neurogenesis include signal transduction pathways, the vascular and immune systems, metabolic factors, and epigenetic regulation. Multiple intrinsic and extrinsic factors such as neurotrophic factors, transcription factors, and cell cycle regulators control neural stem cell proliferation, maintenance in the adult neurogenic niche, and differentiation into mature neurons; these factors act in networks of signaling molecules that influence each other during construction and maintenance of neural circuits, and in turn contribute to learning and memory. The immune system and vascular system are necessary for neuronal formation and neural stem cell fate determination. Inflammatory cytokines regulate adult neurogenesis in response to immune system activation, whereas the vasculature regulates the neural stem cell niche. Vasculature, immune/support cell populations (microglia/astrocytes), adhesion molecules, growth factors, and the extracellular matrix also provide a homing environment for neural stem cells. Epigenetic changes during hippocampal neurogenesis also impact memory and learning. Some genetic variations in neurogenesis related genes may play important roles in the alteration of neural stem cells differentiation into new born neurons during adult neurogenesis, with important therapeutic implications. In this review, we discuss mechanisms of and interactions between these modulators of adult neurogenesis, as well as implications for neurodegenerative disease and current therapeutic research. © 2016 Wiley Periodicals, Inc.

Stimulation of Synaptic Vesicle Exocytosis by the Mental Disease Gene DISC1 is Mediated by N-Type Voltage-Gated Calcium Channels

Lesions and mutations of the DISC1 (Disrupted-in-schizophrenia-1) gene have been linked to major depression, schizophrenia, bipolar disorder and autism, but the influence of DISC1 on synaptic transmission remains poorly understood. Using two independent genetic approaches-RNAi and a DISC1 KO mouse-we examined the impact of DISC1 on the synaptic vesicle (SV) cycle by population imaging of the synaptic tracer vGpH in hippocampal neurons. DISC1 loss-of-function resulted in a marked decrease in SV exocytic rates during neuronal stimulation and was associated with reduced Ca(2+) transients at nerve terminals. Impaired SV release was efficiently rescued by elevation of extracellular Ca(2+), hinting at a link between DISC1 and voltage-gated Ca(2+) channels. Accordingly, blockade of N-type Cav2.2 channels mimics and occludes the effect of DISC1 inactivation on SV exocytosis, and overexpression of DISC1 in a heterologous system increases Cav2.2 currents. Collectively, these results show that DISC1-dependent enhancement of SV exocytosis is mediated by Cav2.2 and point to aberrant glutamate release as a probable endophenotype of major psychiatric disorders.

An interaction between NDE1 and high birth weight increases schizophrenia susceptibility

Pre- and perinatal environmental factors have been shown to increase schizophrenia risk particularly when combined with genetic liability. The investigation of specific gene environment interactions in the etiology of psychiatric disorders has gained momentum. We used multivariate GEE regression modeling to investigate the interaction between genes of the DISC1 pathway and birth weight, in relation to schizophrenia susceptibility in a Finnish schizophrenia family cohort. The study sample consisted of 457 subjects with both genotype and birth weight information. Gender and place of birth were adjusted for in the models. We found a significant interaction between birth weight and two NDE1 markers in relation to increased schizophrenia risk: a four SNP haplotype spanning NDE1 (b=1.26, SE=0.5, p=0.012) and one of its constituent SNPs rs4781678 (b=1.33, SE=0.51, p=0.010). Specifically, high birth weight (>4000g) was associated with increased schizophrenia risk among subjects homozygous for the previously identified risk alleles. The study was based on a family study sample with high genetic loading for schizophrenia and thus our findings cannot directly be generalized as representing the general population. Our results suggest that the functions mediated by NDE1 during the early stages of neurodevelopment are susceptible to the additional disruptive effects of pre- and perinatal environmental factors associated with high birth weight, augmenting schizophrenia susceptibility.

Copy Number Variations in DISC1 and DISC1-Interacting Partners in Major Mental Illness

Robust statistical, genetic and functional evidence supports a role for DISC1 in the aetiology of major mental illness. Furthermore, many of its protein-binding partners show evidence for involvement in the pathophysiology of a range of neurodevelopmental and psychiatric disorders. Copy number variants (CNVs) are suspected to play an important causal role in these disorders. In this study, CNV analysis of DISC1 and its binding partners PAFAH1B1, NDE1, NDEL1, FEZ1, MAP1A, CIT and PDE4B in Scottish and Northern Swedish population-based samples was carried out using multiplex amplicon quantification. Here, we report the finding of rare CNVs in DISC1, NDE1 (together with adjacent genes within the 16p13.11 duplication), NDEL1 (including the overlapping MYH10 gene) and CIT. Our findings provide further evidence for involvement of DISC1 and its interaction partners in neuropsychiatric disorders and also for a role of structural variants in the aetiology of these devastating diseases.

Associating schizophrenia, long non-coding RNAs and neurostructural dynamics

Several lines of evidence indicate that schizophrenia has a strong genetic component. But the exact nature and functional role of this genetic component in the pathophysiology of this mental illness remains a mystery. Long non-coding RNAs (lncRNAs) are a recently discovered family of molecules that regulate gene transcription through a variety of means. Consequently, lncRNAs could help us bring together apparent unrelated findings in schizophrenia; namely, genomic deficiencies on one side and neuroimaging, as well as postmortem results on the other. In fact, the most consistent finding in schizophrenia is decreased brain size together with enlarged ventricles. This anomaly appears to originate from shorter and less ramified dendrites and axons. But a decrease in neuronal arborizations cannot explain the complex pathophysiology of this psychotic disorder; however, dynamic changes in neuronal structure present throughout life could. It is well recognized that the structure of developing neurons is extremely plastic. This structural plasticity was thought to stop with brain development. However, breakthrough discoveries have shown that neuronal structure retains some degree of plasticity throughout life. What the neuroscientific field is still trying to understand is how these dynamic changes are regulated and lncRNAs represent promising candidates to fill this knowledge gap. Here, we present evidence that associates specific lncRNAs with schizophrenia. We then discuss the potential role of lncRNAs in neurostructural dynamics. Finally, we explain how dynamic neurostructural modifications present throughout life could, in theory, reconcile apparent unrelated findings in schizophrenia.

Neuronal migration abnormalities and its possible implications for schizophrenia

Schizophrenia is a complex mental disorder that displays behavioral deficits such as decreased sensory gating, reduced social interaction and working memory deficits. The neurodevelopmental model is one of the widely accepted hypotheses of the etiology of schizophrenia. Subtle developmental abnormalities of the brain which stated long before the onset of clinical symptoms are thought to lead to the emergence of illness. Schizophrenia has strong genetic components but its underlying molecular pathogenesis is still poorly understood. Genetic linkage and association studies have identified several genes involved in neuronal migrations as candidate susceptibility genes for schizophrenia, although their effect size is small. Recent progress in copy number variation studies also has identified much higher risk loci such as 22q11. Based on these genetic findings, we are now able to utilize genetically-defined animal models. Here we summarize the results of neurodevelopmental and behavioral analysis of genetically-defined animal models. Furthermore, animal model experiments have demonstrated that embryonic and perinatal neurodevelopmental insults in neurogenesis and neuronal migrations cause neuronal functional and behavioral deficits in affected adult animals, which are similar to those of schizophrenic patients. However, these findings do not establish causative relationship. Genetically-defined animal models are a critical approach to explore the relationship between neuronal migration abnormalities and behavioral abnormalities relevant to schizophrenia.

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Disrupted-In-Schizophrenia-1 (DISC1) interactome and mental disorders: impact of mouse models

Disrupted-In-Schizophrenia-1 (DISC1) has captured much attention because it predisposes individuals to a wide range of mental illnesses. Notably, a number of genes encoding proteins interacting with DISC1 are also considered to be relevant risk factors of mental disorders. We reasoned that the understanding of DISC1-associated mental disorders in the context of network principles will help to address fundamental properties of DISC1 as a disease gene. Systematic integration of behavioural phenotypes of genetic mouse lines carrying perturbation in DISC1 interacting proteins would contribute to a better resolution of neurobiological mechanisms of mental disorders associated with the impaired DISC1 interactome and lead to a development of network medicine. This review also makes specific recommendations of how to assess DISC1 associated mental disorders in mouse models and discuss future directions.

Alterations of GABAergic and dopaminergic systems in mutant mice with disruption of exons 2 and 3 of the Disc1 gene

Disrupted-in-schizophrenia-1 (DISC1) has been widely associated with several psychiatric disorders, including schizophrenia, mood disorders and autism. We previously reported that a deficiency of DISC1 may induce low anxiety and/or high impulsivity in mice with disruption of exons 2 and 3 of the Disc1 gene (Disc1(Δ2-3/Δ2-3)). It remains unclear, however, if deficiency of DISC1 leads to specific alterations in distinct neuronal systems. In the present study, to understand the role of DISC1 in γ-aminobutyric acid (GABA) interneurons and mesocorticolimbic dopaminergic (DAergic) neurons, we investigated the number of parvalbumin (PV)-positive interneurons, methamphetamine (METH)-induced DA release and the expression levels of GABAA, DA transporter (DAT) and DA receptors in wild-type (Disc1(+/+)) and Disc1(Δ2-3/Δ2-3) mice. Female Disc1(Δ2-3/Δ2-3) mice showed a significant reduction of PV-positive interneurons in the hippocampus, while no apparent changes were observed in mRNA expression levels of GABAA receptor subunits. METH-induced DA release was significantly potentiated in the nucleus accumbens (NAc) of female Disc1(Δ2-3/Δ2-3) mice, although there were no significant differences in the expression levels of DAT. Furthermore, the expression levels of DA receptor mRNA were upregulated in the NAc of female Disc1(Δ2-3/Δ2-3) mice. Male Disc1(Δ2-3/Δ2-3) mice showed no apparent differences in all experiments. DISC1 may play a critical role in gender-specific developmental alteration in GABAergic inhibitory interneurons and DAergic neurons.

A Disrupted-in-Schizophrenia 1 Gene Variant is Associated with Clinical Symptomatology in Patients with First-Episode Psychosis

OBJECTIVE

DISC1 gene is one of the main candidate genes for schizophrenia since it has been associated to the illness in several populations. Moreover, variations in several DISC1 polymorphisms, and in particular Ser704Cys SNP, have been associated in schizophrenic patients to structural and functional modifications in two brain areas (pre-frontal cortex and hippocampus) that play a central role in the genesis of psychotic symptoms. This study tested the association between Ser704Cys DISC1 polymorphism and the clinical onset of psychosis.

METHODS

Two hundred and thirteen Caucasian drug-naive patients experiencing a first episode of non-affective psychosis were genotyped for rs821616 (Ser704Cys) SNP of the DISC1 gene. The clinical severity of the illness was assessed using SAPS and SANS scales. Other clinical and socio-demographic variables were recorded to rule out possible confounding effects.

RESULTS

Patients homozygous for the Ser allele of the Ser704Cys DISC1 SNP had significantly (p<0.05) higher rates at the positive symptoms dimension (SAPS-SANS scales) and hallucinations item, compared to Cys carriers.

CONCLUSION

DISC1 gene variations may modulate the clinical severity of the psychosis at the onset of the disorder.

PSEUDOMARKER 2.0: efficient computation of likelihoods using NOMAD

BACKGROUND

PSEUDOMARKER is a software package that performs joint linkage and linkage disequilibrium analysis between a marker and a putative disease locus. A key feature of PSEUDOMARKER is that it can combine case-controls and pedigrees of varying structure into a single unified analysis. Thus it maximizes the full likelihood of the data over marker allele frequencies or conditional allele frequencies on disease and recombination fraction.

RESULTS

The new version 2.0 uses the software package NOMAD to maximize likelihoods, resulting in generally comparable or better optima with many fewer evaluations of the likelihood functions.

CONCLUSIONS

After being modified substantially to use modern optimization methods, PSEUDOMARKER version 2.0 is more robust and substantially faster than version 1.0. NOMAD may be useful in other bioinformatics problems where complex likelihood functions are optimized.

Parental psychiatric disorders and autism spectrum disorders

The present population-based, case-control study examines associations between specific parental psychiatric disorders and autism spectrum disorders (ASD) including childhood autism, Asperger's syndrome and pervasive developmental disorder (PDD-NOS). The cohort includes 4713 children born between 1987 and 2005 with diagnoses of childhood autism, Asperger's syndrome or PDD-NOS. Cases were ascertained from the Finnish Hospital Discharge Register, and each was matched to four controls by gender, date of birth, place of birth, and residence in Finland. Controls were selected from the Finnish Medical Birth Register. Parents were identified through the Finnish Medical Birth Register and Finnish Central Population Register. Parental psychiatric diagnoses from inpatient care were collected from the Finnish Hospital Discharge Register. Conditional logistic regression models were used to assess whether parents' psychiatric disorders predicted ASD after controlling for parents' age, smoking during pregnancy and weight for gestational age. In summary, parental schizophrenia spectrum disorders and affective disorders were associated with the risk of ASD regardless of the subgroup. PDD-NOS was associated with all parental psychiatric disorders investigated. Further studies are needed to replicate these findings. These results may facilitate the investigation of shared genetic and familial factors between ASD and other psychiatric disorders.

Association study of three microsatellite polymorphisms located in introns 1, 8, and 9 of DISC1 with schizophrenia in the Chinese Han population

AIMS

This study explores more polymorphisms in Disrupted-in-schizophrenia-1 (DISC1) for schizophrenia, which confer risk of developing the disorder.

RESULTS

We report three short tandem repeat (STR) loci ((ATCC)n1, D1S1621, and (ATCC)n2) in DISC1 that showed a significant association with schizophrenia in a set of Chinese Han individuals, including 310 schizophrenics and 400 controls. The STRs in DISC1 associated with schizophrenia occur in intronic sequences in the vicinity of a critical splice junction that gives rise to the expression of DISC1 isoforms. The frequencies of allele 12 of (ATCC)n1, alleles 11 and 12, allele 13 and allele 15 of D1S1621, and allele 10 of (ATCC)n2 were significantly higher in schizophrenia patients than in controls. In contrast, the frequencies of alleles 9 and 10 of (ATCC)n1 and allele 16 and alleles17 and 18 of D1S1621 were significantly lower in schizophrenia patients than in controls.

CONCLUSIONS

Our results provide further evidence for an effect of the DISC1 gene on the etiology of schizophrenia and suggest that STRs in the DISC1 gene may be genetic risk factors for schizophrenia.

An association between both low and high birth weight and increased disorganized and negative symptom severity in schizophrenia and other psychoses

Longitudinal cohort studies have implicated an association between both low and high birth weight and increased schizophrenia risk. In this study, we investigated the effect of birth weight on the symptom severity of psychotic disorders including schizophrenia in a Finnish schizophrenia family study sample. We used a multivariate GEE (General Estimating Equation) regression model to investigate the association of birth weight and symptom severity in 282 subjects with a primary psychotic disorder, 178 of whom had a diagnosis of schizophrenia. The Scales for the Assessment of Positive and Negative Symptoms (SAPS and SANS) were used as a measure of symptom severity. Sex, place of birth and year of birth were adjusted for in the model. Both low and high birth weight were associated with more severe symptoms with respect to bizarre behaviour, affective flattening and attentional impairment. In addition, low birth weight was associated with more severe symptoms with respect to positive formal thought. Our findings suggest that both low and high birth weight can influence the symptom severity of psychotic disorders. Our results implicate an association between both low and high birth weight and disorganized and negative symptoms.

Human pluripotent stem cells: applications and challenges in neurological diseases

The ability to generate human pluripotent stem cells (hPSCs) holds great promise for the understanding and the treatment of human neurological diseases in modern medicine. The hPSCs are considered for their in vitro use as research tools to provide relevant cellular model for human diseases, drug discovery, and toxicity assays and for their in vivo use in regenerative medicine applications. In this review, we highlight recent progress, promises, and challenges of hPSC applications in human neurological disease modeling and therapies.

Proteomic, genomic and translational approaches identify CRMP1 for a role in schizophrenia and its underlying traits

Schizophrenia is a chronic illness of heterogenous biological origin. We hypothesized that, similar to chronic progressive brain conditions, persistent functional disturbances of neurons would result in disturbed proteostasis in the brains of schizophrenia patients, leading to increased abundance of specific misfolded, insoluble proteins. Identification of such proteins would facilitate the elucidation of molecular processes underlying these devastating conditions. We therefore generated antibodies against pooled insoluble proteome of post-mortem brains from schizophrenia patients in order to identify unique, disease-specific epitopes. We successfully identified such an epitope to be present on collapsin-response mediator protein 1 (CRMP1) in biochemically purified, insoluble brain fractions. A genetic association analysis for the CRMP1 gene in a large Finnish population cohort (n = 4651) corroborated the association of physical and social anhedonia with the CRMP1 locus in a DISC1 (Disrupted-in-schizophrenia 1)-dependent manner. Physical and social anhedonia are heritable traits, present as chronic, negative symptoms of schizophrenia and severe major depression, thus constituting serious vulnerability factors for mental disease. Strikingly, lymphoblastoid cell lines derived from schizophrenia patients mirrored aberrant CRMP1 immunoreactivity by showing an increase of CRMP1 expression, suggesting its potential role as a blood-based diagnostic marker. CRMP1 is a novel candidate protein for schizophrenia traits at the intersection of the reelin and DISC1 pathways that directly and functionally interacts with DISC1. We demonstrate the impact of an interdisciplinary approach where the identification of a disease-associated epitope in post-mortem brains, powered by a genetic association study, is rapidly translated into a potential blood-based diagnostic marker.

Molecular genetics of the psychosis phenotype

OBJECTIVE

Relative to recent successes in elucidating the genetic mechanisms associated with complex diseases, including macular degeneration, diabetes mellitus, type 2, heart disease, and cancer, molecular genetic approaches to psychiatric illness have met with more limited success. While factors such as small allelic effects, allelic heterogeneity, and variation in population substructure have received considerable attention in attempt to explain the paucity of significant results in psychiatric genetics, significantly less focus has been directed toward phenotypic factors.

METHOD

Data derived from molecular genetic studies of the psychosis phenotype in patients with a range of psychiatric illnesses are reviewed.

RESULTS

Available data suggest that genes do not respect the boundaries of the current diagnostic system but may confer risk for symptom-based phenotypic variation that traverses those boundaries.

CONCLUSIONS

Molecular genetic studies offer convincing evidence for a relation between genetic variation and symptom-based phenotypic variation within psychiatric illness. These data may provide novel insights into the pathophysiology of schizophrenia and other related disorders. The exploration of relations between genetic variation and symptom variation that traverses traditional diagnostic boundaries may ultimately lead to more refined classification systems that more closely reflect the genetic etiology of psychiatric illness.

Gender-specific association of TSNAX/DISC1 locus for schizophrenia and bipolar affective disorder in South Indian population

Genetic association studies have implicated the TSNAX/DISC1 (disrupted in schizophrenia 1) in schizophrenia (SCZ), bipolar affective disorder (BPAD) and major depression. This study was performed to assess the possible involvement of TSNAX/DISC1 locus in the aetiology of BPAD and SCZ in the Southern Indian population. We genotyped seven single nucleotide polymorphism (SNPs) from TSNAX/DISC1 region in 1252 individuals (419 BPAD patients, 408 SCZ patients and 425 controls). Binary logistic regression revealed a nominal association for rs821616 in DISC1 for BPAD and also combined cases of BPAD or SCZ, but after correcting for multiple testing, these results were non-significant. However, significant association was observed with BPAD, as well as combined cases of BPAD or SCZ, within the female subjects for the rs766288 after applying false discovery rate corrections at the 0.05 level. Two-locus analysis showed C-C (rs766288-rs2812393) as a risk combination in BPAD, and G-T (rs2812393-rs821616) as a protective combination in SCZ and combined cases of BPAD or SCZ. Female-specific associations were observed for rs766288-rs2812393, rs766288-rs821616 and rs8212393-rs821616 in two-locus analysis. Our results provide further evidence for sex-dependent effects of the TSNAX/DISC1 locus in the aetiology of SCZ and BPAD.

Incidental medical information in whole-exome sequencing

Genomic technologies, such as whole-exome sequencing, are a powerful tool in genetic research. Such testing yields a great deal of incidental medical information, or medical information not related to the primary research target. We describe the management of incidental medical information derived from whole-exome sequencing in the research context. We performed whole-exome sequencing on a monozygotic twin pair in which only 1 child was affected with congenital anomalies and applied an institutional review board-approved algorithm to determine what genetic information would be returned. Whole-exome sequencing identified 79525 genetic variants in the twins. Here, we focus on novel variants. After filtering artifacts and excluding known single nucleotide polymorphisms and variants not predicted to be pathogenic, the twins had 32 novel variants in 32 genes that were felt to be likely to be associated with human disease. Eighteen of these novel variants were associated with recessive disease and 18 were associated with dominantly manifesting conditions (variants in some genes were potentially associated with both recessive and dominant conditions), but only 1 variant ultimately met our institutional review board-approved criteria for return of information to the research participants.

The effect of DISC1 on regional gray matter density of schizophrenia in Han Chinese population

Schizophrenia is thought to arise in part from abnormal gray matter (GM), which are partly shared by the relatives of the probands. DISC1 is one of the most promising susceptibility genes of schizophrenia and a SNP rs821597 (A) in the gene was associated with schizophrenia in Han Chinese population. In this study, 61 healthy controls and 72 with schizophrenic patients were genotyped at rs821597, and underwent T1-weighted MRI for the density of GM. The results showed that the risk allele (A) carriers had higher GM density in regional left parahippocampal gyrus and right orbitofrontal cortex in schizophrenic patients, but had reduced GM density of these brain regions in healthy controls. The DISC1 variant rs821597 may confer risk for schizophrenia by its effects on the regional GM in left parahippocampal gyrus and right orbitofrontal cortex with other risk factors for schizophrenia.

Aggregated proteins in schizophrenia and other chronic mental diseases: DISC1opathies

Chronic mental diseases (CMD) like the schizophrenias are progressive diseases of heterogenous but poorly understood biological origin. An imbalance in proteostasis is a hallmark of dysfunctional neurons, leading to impaired clearance and abnormal deposition of protein aggregates. Thus, it can be hypothesized that unbalanced proteostasis in such neurons may also lead to protein aggregates in schizophrenia. These protein aggregates, however, would be more subtle then in the classical neurodegenerative diseases and as such have not yet been detected. The DISC1 (Disrupted-in-schizophrenia 1) gene is considered among the most promising candidate genes for CMD having been identified as linked to CMD in a Scottish pedigree and having since been found to associate to various phenotypes of CMD. We have recently demonstrated increased insoluble DISC1 protein in the cingular cortex in approximately 20% of cases of CMD within the widely used Stanley Medical Research Institute Consortium Collection. Surprisingly, in vitro, DISC1 aggregates were cell-invasive, i.e., purified aggresomes or recombinant DISC1 fragments where internalized at an efficiency comparable to that of α-synuclein. Intracellular DISC1 aggresomes acquired gain-of-function properties in recruiting otherwise soluble proteins such as the candidate schizophrenia protein dysbindin. Disease-associated DISC1 polymorphism S704C led to a higher oligomerization tendency of DISC1. These findings justify classification of DISC1-dependent brain disorders as protein conformational disorders which we have tentatively termed DISC1opathies. The notion of disturbed proteostasis and protein aggregation as a mechanism of mental diseases is thus emerging. The yet unidentified form of neuronal impairment in CMD is more subtle than in the classical neurodegenerative diseases without leading to massive cell death and as such present a different kind of neuronal dysfunctionality, eventually confined to highly selective CNS subpopulations.

Comprehensive behavioral analysis of ENU-induced Disc1-Q31L and -L100P mutant mice

Background

Disrupted-in-Schizophrenia 1 (DISC1) is considered to be a candidate susceptibility gene for psychiatric disorders, including schizophrenia, bipolar disorder, and major depression. A recent study reported that N-ethyl-N-nitrosourea (ENU)-induced mutations in exon 2 of the mouse Disc1 gene, which resulted in the amino acid exchange of Q31L and L100P, caused an increase in depression-like behavior in 31 L mutant mice and schizophrenia-like behavior in 100P mutant mice; thus, these are potential animal models of psychiatric disorders. However, remaining heterozygous mutations that possibly occur in flanking genes other than Disc1 itself might induce behavioral abnormalities in the mutant mice. Here, to confirm the effects of Disc1-Q31L and Disc1-L100P mutations on behavioral phenotypes and to investigate the behaviors of the mutant mice in more detail, the mutant lines were backcrossed to C57BL/6JJcl through an additional two generations and the behaviors were analyzed using a comprehensive behavioral test battery.

Results

Contrary to expectations, 31 L mutant mice showed no significant behavioral differences when compared with wild-type control mice in any of the behavioral tests, including the Porsolt forced swim and tail suspension tests, commonly used tests for depression-like behavior. Also, 100P mutant mice exhibited no differences in almost all of the behavioral tests, including the prepulse inhibition test for measuring sensorimotor gating, which is known to be impaired in schizophrenia patients; however, 100P mutant mice showed higher locomotor activity compared with wild-type control mice in the light/dark transition test.

Conclusions

Although these results are partially consistent with the previous study in that there was hyperactivity in 100P mutant mice, the vast majority of the results are inconsistent with those of the previous study; this discrepancy may be explained by differences in the genetic background of the mice, the laboratory environment, experimental protocols, and more. Further behavioral studies under various experimental conditions are necessary to determine whether these Disc1 mutant mouse lines are suitable animal models of schizophrenia and major depression.

Clinical applications of schizophrenia genetics: genetic diagnosis, risk, and counseling in the molecular era

Schizophrenia is a complex neuropsychiatric disease with documented clinical and genetic heterogeneity, and evidence for neurodevelopmental origins. Driven by new genetic technologies and advances in molecular medicine, there has recently been concrete progress in understanding some of the specific genetic causes of this serious psychiatric illness. In particular, several large rare structural variants have been convincingly associated with schizophrenia, in targeted studies over two decades with respect to 22q11.2 microdeletions, and more recently in large-scale, genome-wide case-control studies. These advances promise to help many families afflicted with this disease. In this review, we critically appraise recent developments in the field of schizophrenia genetics through the lens of immediate clinical applicability. Much work remains in translating the recent surge of genetic research discoveries into the clinic. The epidemiology and basic genetic parameters (such as penetrance and expression) of most genomic disorders associated with schizophrenia are not yet well characterized. To date, 22q11.2 deletion syndrome is the only established genetic subtype of schizophrenia of proven clinical relevance. We use this well-established association as a model to chart the pathway for translating emerging genetic discoveries into clinical practice. We also propose new directions for research involving general genetic risk prediction and counseling in schizophrenia.

An association between high birth weight and schizophrenia in a Finnish schizophrenia family study sample

Longitudinal cohort studies have implicated an association between both low and high birth weight and schizophrenia. It has been suggested that schizophrenia associated genes could augment an individual's susceptibility to adverse prenatal and perinatal environmental events. We investigated the association between birth weight and schizophrenia in a large Finnish schizophrenia family study sample. We utilized the birth weight data of 1051 offspring from 315 Finnish families with at least one offspring with a diagnosis of schizophrenia. We used a multivariate COX frailty model to analyze the effect of birth weight on the risk of developing schizophrenia within the families. Using information from the Medication Reimbursement Register and patient interviews, we further investigated the association of maternal type 2 diabetes and schizophrenia risk among offspring. High birth weight (>4000g) was associated with a 1.68-fold increase in schizophrenia susceptibility. Maternal diabetes at the time of data collection, a proxy for gestational diabetes, was associated with a 1.66-fold increase in the risk of developing schizophrenia among offspring. Our results corroborate recent findings showing an association between high birth weight and schizophrenia. Our results also point to a potential birth-weight independent association between maternal type 2 diabetes and schizophrenia among offspring.

Concise review: the promise of human induced pluripotent stem cell-based studies of schizophrenia

Schizophrenia (SCZD) is a heritable developmental disorder. Although the molecular mechanism of disease remains unclear, insights into the disorder have been made through a vast array of experimental techniques. Together, magnetic resonance brain imaging, pharmacological, and post-mortem pathological studies have observed decreased brain volume, aberrant neurotransmitter signaling, reduced dendritic arborization, and impaired myelination in SCZD. Genome-wide association studies (GWAS) have identified common single nucleotide polymorphisms as well as rare copy number variants that contribute to SCZD, while mouse models of candidate SCZD genes show behavioral abnormalities and anatomical perturbations consistent with human disease. The advent of human induced pluripotent stem cells (hiPSCs) makes it possible to study SCZD using live human neurons with a genetic predisposition toward SCZD, even without knowledge of the genes interacting to produce the disease state. SCZD hiPSC neurons show cellular defects comparable to those identified in post-mortem human and mouse studies, and gene expression changes are consistent with predictions made by GWAS. SCZD hiPSC neurons represent a new tool to look beyond phenotype and begin to dissect the molecular mechanisms of SCZD.

Impact of DISC1 variation on neuroanatomical and neurocognitive phenotypes

Although disrupted in schizophrenia 1 (DISC1) has been implicated in many psychiatric disorders, including schizophrenia, bipolar disorder, schizoaffective disorder and major depression, its biological role in these disorders is unclear. To better understand this gene and its role in psychiatric disease, we conducted transcriptional profiling and genome-wide association analysis in 1232 pedigreed Mexican-American individuals for whom we have neuroanatomic images, neurocognitive assessments and neuropsychiatric diagnoses. SOLAR was used to determine heritability, identify gene expression patterns and perform association analyses on 188 quantitative brain-related phenotypes. We found that the DISC1 transcript is highly heritable (h(2)=0.50; P=1.97 × 10(-22)), and that gene expression is strongly cis-regulated (cis-LOD=3.89) but is also influenced by trans-effects. We identified several DISC1 polymorphisms that were associated with cortical gray matter thickness within the parietal, temporal and frontal lobes. Associated regions affiliated with memory included the entorhinal cortex (rs821639, P=4.11 × 10(-5); rs2356606, P=4.71 × 10(-4)), cingulate cortex (rs16856322, P=2.88 × 10(-4)) and parahippocampal gyrus (rs821639, P=4.95 × 10(-4)); those affiliated with executive and other cognitive processing included the transverse temporal gyrus (rs9661837, P=5.21 × 10(-4); rs17773946, P=6.23 × 10(-4)), anterior cingulate cortex (rs2487453, P=4.79 × 10(-4); rs3738401, P=5.43 × 10(-4)) and medial orbitofrontal cortex (rs9661837; P=7.40 × 10(-4)). Cognitive measures of working memory (rs2793094, P=3.38 × 10(-4)), as well as lifetime history of depression (rs4658966, P=4.33 × 10(-4); rs12137417, P=4.93 × 10(-4)) and panic (rs12137417, P=7.41 × 10(-4)) were associated with DISC1 sequence variation. DISC1 has well-defined genetic regulation and clearly influences important phenotypes related to psychiatric disease.

Detection of intergenerational genetic effects with application to HLA-B matching as a risk factor for schizophrenia

BACKGROUND AND METHODS

Association studies using unrelated individuals cannot detect intergenerational genetic effects contributing to disease. To detect these effects, we improve the extended maternal-fetal genotype (EMFG) incompatibility test to estimate any combination of maternal effects, offspring effects, and their interactions at polymorphic loci or multiple SNPs, using any size pedigrees. We explore the advantages of using extended pedigrees rather than nuclear families. We apply our methods to schizophrenia pedigrees to investigate whether the previously associated mother-daughter HLA-B matching is a genuine risk or the result of bias.

RESULTS

Simulations demonstrate that using the EMFG test with extended pedigrees increases power and precision, while partitioning extended pedigrees into nuclear families can underestimate intergenerational effects. Application to actual data demonstrates that mother-daughter HLA-B matching remains a schizophrenia risk factor. Furthermore, ascertainment and mate selection biases cannot by themselves explain the observed HLA-B matching and schizophrenia association.

CONCLUSIONS

Our results demonstrate the power of the EMFG test to examine intergenerational genetic effects, highlight the importance of pedigree rather than case/control or case-mother/control-mother designs, illustrate that pedigrees provide a means to examine alternative, non-causal mechanisms, and they strongly support the hypothesis that HLA-B matching is causally involved in the etiology of schizophrenia in females.

On the statistical properties of family-based association tests in datasets containing both pedigrees and unrelated case-control samples

A common approach to genetic mapping of loci for complex diseases is to perform a genome-wide association study (GWAS) by analyzing a vast number of SNP markers in cohorts of unrelated cases and controls. A direct motivation for the case-control design is that unrelated, affected individuals can be easier to collect than large families with multiple affected persons in the Western world. Despite its higher potential power, investigators have not actively pursued family ascertainment in part because of a dearth of methods for analyzing such correlated data on a large scale. We examine the statistical properties of several commonly used family-based association tests, as to their performance using real-life mixtures of families and singletons taken from our own migraine and schizophrenia studies, as well as population-based data for a complex trait simulated with the evolutionary phenogenetic simulator, ForSim. In virtually every situation, the full likelihood-based methods in the PSEUDOMARKER program outperformed those implemented in FBAT, GENEHUNTER TDT, PLINK (family-based options), HRR/HHRR, QTDT, TRANSMIT, UNPHASED, MENDEL, and LAMP. We further show that GWAS is much more powerful when family samples are used rather than unrelateds, on a genotype-by-genotype basis.

Sequencing of DISC1 pathway genes reveals increased burden of rare missense variants in schizophrenia patients from a northern Swedish population

In recent years, DISC1 has emerged as one of the most credible and best supported candidate genes for schizophrenia and related neuropsychiatric disorders. Furthermore, increasing evidence--both genetic and functional--indicates that many of its protein interaction partners are also involved in the development of these diseases. In this study, we applied a pooled sample 454 sequencing strategy, to explore the contribution of genetic variation in DISC1 and 10 of its interaction partners (ATF5, Grb2, FEZ1, LIS-1, PDE4B, NDE1, NDEL1, TRAF3IP1, YWHAE, and ZNF365) to schizophrenia susceptibility in an isolated northern Swedish population. Mutation burden analysis of the identified variants in a population of 486 SZ patients and 514 control individuals, revealed that non-synonymous rare variants with a MAF<0.01 were significantly more present in patients compared to controls (8.64% versus 4.7%, P = 0.018), providing further evidence for the involvement of DISC1 and some of its interaction partners in psychiatric disorders. This increased burden of rare missense variants was even more striking in a subgroup of early onset patients (12.9% versus 4.7%, P = 0.0004), highlighting the importance of studying subgroups of patients and identifying endophenotypes. Upon investigation of the potential functional effects associated with the identified missense variants, we found that ∼90% of these variants reside in intrinsically disordered protein regions. The observed increase in mutation burden in patients provides further support for the role of the DISC1 pathway in schizophrenia. Furthermore, this study presents the first evidence supporting the involvement of mutations within intrinsically disordered protein regions in the pathogenesis of psychiatric disorders. As many important biological functions depend directly on the disordered state, alteration of this disorder in key pathways may represent an intriguing new disease mechanism for schizophrenia and related neuropsychiatric diseases. Further research into this unexplored domain will be required to elucidate the role of the identified variants in schizophrenia etiology.