Effects of psychosis-associated genetic markers on brain volumetry: a systematic review of replicated findings and an independent validation

© The Author(s), 2022. Published by Cambridge University Press. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.Background: Given psychotic illnesses' high heritability and associations with brain structure, numerous neuroimaging-genetics findings have been reported in the last two decades. However, few findings have been replicated. In the present independent sample we aimed to replicate any psychosis-implicated SNPs (single nucleotide polymorphisms), which had previously shown at least two main effects on brain volume. Methods: A systematic review for SNPs showing a replicated effect on brain volume yielded 25 studies implicating seven SNPs in five genes. Their effect was then tested in 113 subjects with either schizophrenia, bipolar disorder, 'at risk mental state' or healthy state, for whole-brain and region-of-interest (ROI) associations with grey and white matter volume changes, using voxel-based morphometry. Results: We found FWER-corrected (Family-wise error rate) (i.e. statistically significant) associations of: (1) CACNA1C-rs769087-A with larger bilateral hippocampus and thalamus white matter, across the whole brain; and (2) CACNA1C-rs769087-A with larger superior frontal gyrus, as ROI. Higher replication concordance with existing literature was found, in decreasing order, for: (1) CACNA1C-rs769087-A, with larger dorsolateral-prefrontal/superior frontal gyrus and hippocampi (both with anatomical and directional concordance); (2) ZNF804A-rs11681373-A, with smaller angular gyrus grey matter and rectus gyri white matter (both with anatomical and directional concordance); and (3) BDNF-rs6265-T with superior frontal and middle cingulate gyri volume change (with anatomical and allelic concordance). Conclusions: Most literature findings were not herein replicated. Nevertheless, high degree/likelihood of replication was found for two genome-wide association studies- and one candidate-implicated SNPs, supporting their involvement in psychosis and brain structure.VT was supported by a Fundação para a Ciência e Tecnologia (FCT) PhD fellowship (PD/BD/114460/2016) and hired on the FCT DSAIPA/DS/0065/2018 grant. DP was supported, during this work, by the European Commission Seventh Framework Programme Marie Curie Career Integration Grant FP7-PEOPLE-2013-CIG-631952, the 2016 Bial Foundation Psychophysiology Grant – Ref. 292/16, and the FCT IF/00787/2014, LISBOA-01-0145-FEDER-030907, DSAIPA/DS/0065/2018 and UIDB/00645/2020 grants, and the Instituto de Medicina Molecular (iMM) Lisboa Director's Fund Breakthrough Idea Grant 2016.info:eu-repo/semantics/publishedVersio

Prenatal isolated mild ventriculomegaly is associated with persistent ventricle enlargement at ages 1 and 2

Enlargement of the lateral ventricles is thought to originate from abnormal prenatal brain development and is associated with neurodevelopmental disorders. Fetal isolated mild ventriculomegaly (MVM) is associated with enlargement of lateral ventricle volumes in the neonatal period and developmental delays in early childhood. However, little is known about postnatal brain development in these children

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 disorde

DISC1 genetics, biology and psychiatric illness

Psychiatric disorders are highly heritable, and in many individuals likely arise from the combined effects of genes and the environment. A substantial body of evidence points towards DISC1 being one of the genes that influence risk of schizophrenia, bipolar disorder and depression, and functional studies of DISC1 consequently have the potential to reveal much about the pathways that lead to major mental illness. Here, we review the evidence that DISC1 influences disease risk through effects upon multiple critical pathways in the developing and adult brain

The DISC1 Pathway in the Genetic Etiology of Schizophrenia

Schizophrenia is a severe psychotic disorder affecting 0.5-1 % of the population. The disorder is characterized by hallucinations; delusions; disorganized behavior and speech; avolition; anhedonia; flattened affect and cognitive deficits. The etiology of the disorder is complex with evidence for multiple genes contributing to the onset of the disorder along with environmental factors. DISC1 is one of the most promising candidate genes for schizophrenia. It codes for a protein which takes part in numerous molecular interactions along several pathways. This network, termed as the DISC1 pathway, is evidently important for the development and maturation of the central nervous system from the embryo until young adulthood. Disruption at these pathways is thought to predispose schizophrenia. In the present study, we have studied the DISC1 pathway in the etiology of schizophrenia in the Finnish population. We have utilized large Finnish samples; the schizophrenia family sample where DISC1 was originally shown to associate with schizophrenia and the Northern Finland birth cohort 1966 (NFBC66). Several DISC1 binding partners displayed evidence for association in the family sample along with DISC1. Through a genome-wide linkage study, we found a significant linkage signal to a locus where a DISC1 binding partner NDE1 is located at the carriers of a certain DISC1 risk variant. In a follow-up study, genetic markers in NDE1 displayed significant evidence for association with schizophrenia. Further exploration of association between 11 genes of the DISC1 pathway and schizophrenia led to recognition of novel variants in NDEL1, PDE4B and PDE4D that significantly either increased or decreased the risk for schizophrenia. Further, we found evidence that DISC1 itself has a significant role in the human mental functioning even in the healthy population. Variants in DISC1 had a significant effect on anhedonia which is a trait present at everybody but is in its severe form one of the main symptoms of schizophrenia and correlates with the risk of developing the disorder. Further, utilizing genome-wide marker data, we recognized three genes; MIR620; CCDC141 and LCT; that are closely related to the DISC1 pathway but which effects on anhedonia were observable only at the individuals who carried these specific DISC1 variants. Our findings significantly add up to the previous evidence for the involvement of DISC1 and the DISC1 pathway in the etiology of schizophrenia and psychosis. Our results support the concept of a number of DISC1 pathway related genes contributing in the etiology of schizophrenia along with DISC1 and provide new candidates for the studies of schizophrenia. Our findings also significantly increase the importance of DISC1 itself as having a role in psychological functioning in the general population.Skitsofrenia on vakava psykoottinen mielenterveyden häiriö, jota sairastaa 0.5-1 % väestöstä. Skitsofrenian tyypillisiin oireisiin kuuluvat aistiharhat, harhaluulot, hajanainen puhe ja käytös, kiinnostuksen puute, vähentynyt kyky tuntea mielihyvää (anhedonia), tunteiden ilmaisun köyhyys sekä kongtiviivisen kyvyn alentuminen. Skitsofrenian tausta on monitekijäinen, eli sairauden puhkeamiseen vaikuttavat useat geneettiset sekä ympäristötekijät yhdessä. DISC1 on yksi lupaavimmista skitsofrenian ehdokasgeeneistä. DISC1:n koodaama proteiini vuorovaikuttaa monien muiden proteiinien kanssa (DISC1-polku) osallistuen lukuisiin prosesseihin, jotka ovat nykykäsityksen mukaan tärkeitä keskushermoston kehityksessä sikiökaudelta varhaiseen aikuisuuteen ja joiden häiriintyminen voi altistaa skitsofrenialle. Tässä tutkimuksessa olemme kartoittaneet DISC1-polun merkitystä skitsofrenian taustatekijänä suomalaisessa väestössä. Käytössämme on ollut laaja skitsofreniaperheaineisto, jossa aiemmin on havaittu yhteys DISC1:n ja skitsofrenian välillä, sekä suuri pohjoissuomalainen syntymäkohortti vuodelta 1966. Perheaineistossa DISC1:n ohella myös useat muut DISC1-polun geenit osoittautuivat olevan yhteydessä skitsofreniaan. Genominlaajuisessa analyysissä havaitsimme kytkentäsignaalin lähellä DISC1:n kanssa vuorovaikuttavaa NDE1:tä henkilöillä, jotka kantoivat tiettyä DISC1-riskimuotoa. Tarkemmassa assosiaatioanalyysissä kartoitimme tämän ja 11 muun tunnetun DISC1-polun geenin yhteyttä skitsofreniaan ja tunnistimme geeneissä NDE1, NDEL1, PDE4B ja PDE4D uusia variantteja, jotka olivat yhteydessä joko kohonneesseen tai alentuneeseen skitsofreniariskiin. Tulostemme perusteella DISC1:llä näyttää olevan tärkeä rooli myös terveen väestön käyttäytymiselle. Tietyt DISC1:n muodot näyttävät olevan yhteydessä anhedoniaan, joka on kaikilta mitattavissa oleva ominaisuus, mutta joka vaikeassa muodossaan on yksi skitsofrenian pääoireista ja korreloi skitsofreniaan sairastumisen riskin kanssa. Lisäksi genominlaajuisessa aineistossa tunnistimme kolme geeniä, MIR620, CCDC141 ja LCT, jotka läheisesti liittyvät DISC1-polkuun ja joiden yhteys anhedoniaan oli havaittavissa vain näiden tiettyjen DISC1-muotojen kantajilla. Löydöksemme tuovat uutta tietoa DISC1:n ja DISC1-polun merkityksestä skitsofrenian ja psykoosialttiuden taustatekijänä suomalaisessa väestössä. Tuloksemme tukevat aiempaa käsitystä siitä, että useat DISC1-polun geenit vaikuttavat skitsofrenia-alttiuteen DISC1:n ohella ja tarjoavat uusia ehdokasgeenejä tarkempia jatkotutkimuksia varten. Se, että DISC1:llä näyttää olevan yhteys käyttäytymiseen myös väestötasolla, tekee DISC1:stä entistäkin merkityksellisemmän ihmisen psyykkisten toimintojen kannalta

Common Gene Variants in Schizophrenia Susceptibility with Focus on Neurodevelopment

Schizophrenia is a severe multifactorial mental disorder with an important and complex genetic component, and the understanding of the underlying biological mechanisms is limited. Several lines of evidence support that abnormal neurodevelopment is involved, such as cognitive deficits in children who later develop schizophrenia, abnormalities in brain structure in the early phase of disease, and aberrant neuronal distributions. Also, glutamatergic dysfunctions are suggested in the schizophrenia etiology, and glutamate signalling is important during neurodevelopment. Perineuronal nets are extracellular matrix structures involved in brain maturation, which includes the characteristic neural epitope Human Natural Killer-1 (HNK-1). To investigate if common gene variants important for neurodevelopment are involved in schizophrenia etiology, we used candidate gene-based association studies of tagSNPs spanning thirty genes, genotyped in a large Scandinavian case-control sample (SCOPE). Nineteen, out of the 289 tagSNPs in 18 neuronal migration genes, were nominally significant, and the strongest finding was a tagSNP located in MAM domain containing glycosylphosphatidylinositol anchor 1 (MDGA1), but no findings were significant after correction. Phosphodiesterase 4B (PDE4B) is a Disrupted-in-Schizophrenia-1 (DISC1) interactor, with previously reported genetic associations only in women. Six and 16, out of 40 and 72 PDE4B tagSNPs, were nominally associated with schizophrenia and bipolar disorder, respectively, in the combined samples or in gender-specific subgroups. No findings were significant after correction. However, two of the tagSNPs nominally associated in schizophrenia females had proxies which were nominally associated in the total bipolar disorder sample, and the four SNPs were located in the same block, surrounding the splice site for the PDE4B3 isoform. Five out of 104 tagSNPs in ten genes involved in perineuronal net formation and HNK-1 biosynthesis, located in beta-1,3-glucuronyltransferase 2 (B3GAT2), were nominally associated with schizophrenia. The association signal for tagSNPs in one of the LD blocks was replicated by proxy SNPs in a much larger European sample (SGENE-plus). Six out of 30 tagSNPs in glutamate receptor ionotrophic kainate 3 (GRIK3) were nominally associated, and the best tagSNP were significant after correction, with increased significance in the Swedish subsample, as well as when the risk allele was combined with another tagSNP risk allele. When investigating clinical characteristics, including positive and negative symptom scores, age at onset, and cognitive measures of learning, memory and IQ, for association with a subset of the tagSNPs and genes included in the thesis studies, there were no significant associations after correction. The current results indicate that gene variants involved in neurodevelopment are associated with schizophrenia, which further supports the neurodevelopmental hypothesis

Neuregulin 1-Erbb4 in the rodent prefrontal cortex: Investigations of schizophrenia-related behaviours and signalling pathways

Schizophrenia is a severe, chronic and debilitating psychiatric disorder. Current therapies have no efficacy in treating the cognitive impairments which are largely responsible for the poor quality of life of schizophrenia patients and contribute to the massive economic burden that is associated with the disorder. Although it is known that schizophrenia is highly heritable, the underlying genetic basis is still poorly understood due to the complex polygenetic nature of the disorder. Several candidate genes which are thought to increase risk for the incidence of schizophrenia have been identified. Two such schizophrenia candidate genes are neuregulin 1 (NRG1) and v-erb-a erythroblastic leukaemia viral oncogene homolog 4 (ERBB4). As well as the genetic evidence from genetic association studies, studies of animal models and the endogenous biological functions of NRG1 and ERBB4 in the CNS suggest that these genes may play an important role in the pathophysiology of schizophrenia. However, very little is known about the functions of these genes in specific brain regions in adulthood with respect to cognition. To address this, I have utilised recombinant adeno-associated viral particles (rAAVs) as a vehicle to mediate knockdown of the expression of Erbb4 specifically within the medial prefrontal (mPFC) cortex of adult rats. This allows for a spatially and temporally controlled investigation of the role that Erbb4 signalling may play in prefrontal cortex-dependent behaviours in adulthood. Following initial in vitro and in vivo validation of the functionality of the rAAVs, further in vivo studies confirmed that, five weeks after stereotaxic injection of rAAVs encoding a short hairpin sequence corresponding to Erbb4 (shErbb4.rAAV), into the mPFC of rats, there was significant Erbb4 protein knockdown, as analysed by ELISA. Subsequent western blot analysis revealed that Erbb4 knockdown consequently increased the level of Nrg1 expression and decreased the activity of Akt signalling, but had no effect on Erk signalling. Erbb4 knockdown specifically within the mPFC increased performance accuracy in the 5-choice serial reaction time task at 5 weeks post-surgery. Furthermore, viral mediated Erbb4 knockdown specifically within the mPFC heightened the II sensitivity to the locomotor inducing effects of amphetamine. There were, however, no effects of Erbb4 knockdown on pre-pulse inhibition at any time points assessed. These results indicate that Nrg1-Erbb4 signalling in the PFC modulates cognitive performance but not sensorimotor gating, and that dopaminergic transmission may be regulated by Nrg1-Erbb4 signalling. In conclusion, this study highlights the ability of viral mediated gene manipulation to investigate regionally specific roles of schizophrenia candidate genes in adulthood in terms of cognition and downstream signalling pathways. This may translate to a better understanding of how these genes may exert potentially pathophysiological effects in patients and ultimately lead to improved treatments

Identification and Evaluation of Endophenotypes and Biomarkers of Schizophrenia and Bipolar Disorder: Genomic Dissection of the Psychosis Phenotype

Background: Psychotic disorders affect approximately 3% of the population. Over 100 genetic variants have been associated with schizophrenia and about 50 with bipolar disorder. Each of them individually has a small effect on disease risk but combined in a cumulative polygenic risk score (PRS), they have a major impact. Copy number variants (CNVs) have also been associated with schizophrenia. However, little is known about their functional effects. The investigation of endophenotypes, which fall in the genotype to phenotype pathway, could help us understand the role of genetic variants and their mechanisms. Methods: In chapter 1 of my thesis, I reviewed the literature on endophenotypes, and genetic variants associated with psychosis, which revealed that the interrelationships between several well-established cognitive, neuroimaging and electrophysiological psychosis endophenotypes, and the joint contributions of CNV burden and polygenic risk scores on psychosis risk have not been studied yet. I investigated those topics in chapters 3 and 4 respectively. In chapter 2 I carried out a scoping review of CNVs associated with neurodevelopmental disorders, psychosis and cognition and carried out a meta-analysis of 16p11.2 distal deletion in schizophrenia. I also investigated the influences of CNV size on schizophrenia risk for 53 CNVs. For all the analyses, I used CNVcatalog, which is a new repository me and my supervisors created, incorporating data from published studies examining associations of CNV loci with several clinical phenotypes, including schizophrenia. Finally, in chapter 5 I summarise the main findings of my thesis and I discuss the strengths, limitations and clinical implications of my research. Results: Chapter 2: The meta-analysis of 16p11.2 distal deletion in schizophrenia revealed that carriers of that CNV had higher risk of developing schizophrenia compared to non carriers. I also found that larger CNV size was associated with larger effect sizes when examining all CNVs together (both deletions and duplications) and CNV deletions. However, the size was not significanly associated with disease risk for CNV duplications. Chapter 3: All the cognitive endophenotypes were associated with each other. Endophenotypes across imaging, cognitive and electrophysiological domains did not show a correlation. The relationships between pairs of endophenotypes were consistent in all three participant groups (cases with psychosis, their unaffected relatives and healthy controls), differing for some of the cognitive pairings only in the strengths of the relationships. Chapter 4: I examined the joint contributions of CNV burden and polygenic risk scores on psychosis risk. I analysed two datasets separately and then combined them by meta-analysis. CNV burden and PRS could explain 11.8% and 10.8% of the variance in disease risk in each dataset. The classification accuracy of my models was 81%, 83% and 77% for the comparisons of all psychosis cases vs controls, schizophrenia cases vs controls and bipolar cases vs controls respectively. The addition of CNV burden to the models increased the variance explained only by 0.1% for MPL dataset and by 0.08% in the PEIC dataset. Discussion: Findings from my thesis contribute to our current knowledge on psychosis endophenotypes and on the genetic influences in psychoses. Deciphering the genetic architecture of psychotic disorders could hopefully in the future improve the lives of affected individuals

Childhood neurodevelopmental factors and risk of psychotic experiences in early adolescence: genotypic variation and developmental endophenotypes

This thesis was about understanding the childhood developmental factors that may lead to psychotic experiences in early adolescence. It also contributed to efforts towards preventative strategies for children with a high risk of psychotic symptoms, and arguably schizophrenia. Based on the findings, the author concluded, that further research on this topic should focus on the development of early detection methods and interventions for high risk children