Dissertation (PhD)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: Obsessive-compulsive disorder is a severe, debilitating psychiatric disorder for which the
underlying molecular aetiology still remains unclear. Evidence from family studies have
suggested that OCD may be caused by a complex interplay of environmental and genetic
factors.
In order to identify the genetic factors that mediate OCD susceptibility, several genetic
association studies have been undertaken, which have yielded inconsistent findings. Moreover,
the majority of these studies have focused on a small number of candidate genes that encode
components of the serotonin and dopamine neurotransmitter pathways. However, based on the
complexity of clinical manifestations observed in OCD, it is likely that its pathogenesis is
mediated by a broader complex of interrelated neurotransmitter systems and signal transduction
pathways; consequently there is a need to identify and assess novel candidate genes.
One method of identifying such novel OCD candidate genes is by utilising knowledge of diseases
with phenomenological overlap with OCD, which lend themselves to better genetic dissection
through linkage analysis and animal studies. Genetic loci for such disorders, identified though
linkage analysis, could potentially harbour novel OCD candidate genes, while genes implicated
through animal models may lead to the identification of additional susceptibility genes through
delineation of pathways by, for instance, interactome analysis. One such disorder is
schizophrenia, which manifests overlap in both symptoms and brain circuits with OCD. In
schizophrenia, in addition to several case-control association studies having been performed,
linkage data, studies of chromosomal aberrations and animal models have led to the identification
of many chromosomal regions that may contain genes involved in its aetiology and thus may also
contain OCD candidate genes.
In the present investigation, this approach was employed using previously reported schizophrenia
susceptibility loci to identify novel OCD candidate genes. All genes residing in each of these loci
were catalogued and individually analysed using a battery of bioinformatic techniques in order to
assess their potential candidature for OCD susceptibility. These analyses yielded 13 credible
OCD candidate genes.Additional candidates were sought using information regarding a well-defined schizophrenia
animal model, the heterozygous reeler mouse, that exhibits neurodevelopmental, neuroanatomical
and behavioural abnormalities, similar to those displayed by patients with schizophrenia. The
phenotype of these mice is caused by a mutation in Reln, which encodes reelin, a large
extracellular matrix protein that plays a pivotal role in the ordered migration of neurons during
the development of laminar brain structures. The fact that both reelin protein and mRNA levels
have been shown to be reduced in post-mortem brain sections of schizophrenic patients, coupled
with the observed behaviour and neurochemical similarities between the heterozygous reeler
mouse and schizophrenic patients suggests that reelin may be involved in the pathogenesis of
schizophrenia and hence also OCD. Furthermore, genes encoding proteins that interact with reelin
may thus also be considered plausible candidate genes for both schizophrenia and OCD. For this
reason, novel reelin-interacting proteins were sought using the N-terminal reeler-domain of
reelin, a domain only found in proteins involved in neuronal migration, as “bait” in a yeast twohybrid
screen of a foetal brain cDNA library. Putative reelin ligands were subsequently reevaluated
using co-immunopreciptitation and mammalian two-hybrid analysis to corroborate the
yeast two-hybrid findings. Results of these analyses showed that WDR47, a WD40-repeat domain
protein, interacts with reelin via its reeler-domain; therefore, the gene encoding this ligand
protein, as well as RELN itself, was also considered a credible OCD candidate gene.
Each of the candidate genes identified using the afore-mentioned strategies were assessed for
their potential role in the aetiology of OCD by case-control association studies of a cohort of
Afrikaner OCD patients and control individuals. Statistically significant associations were
detected for two genes, DLX6 and SYN3, with the disorder. These associations are exciting as
they may point to novel mechanisms involved in OCD development.
The identification of WDR47 as a novel reelin-interacting protein has significant implications for
our understanding of reelin-dependant signalling. Using this protein as the starting point, further
novel components of the reelin signalling pathway may be unravelled, an investigation which
may lead to the identification of novel roles for reelin in neurodevelopment. Such novel
components may, of course, also be considered OCD and schizophrenia candidate genes, which
may, in turn, augment the existing knowledge of the pathophysiologies of OCD, schizophrenia
and other neurodevelopmental disorders. Taken together, the current study yielded exciting results that warrants follow-up investigation in
future. The identification of DLX6 and SYN3 as novel OCD susceptibility genes as well as the
identification of WDR47 as a reelin-interacting protein may provide investigators with alternative
avenues of research into potential pathological mechanisms involved both in OCD and
schizophrenia, which may ultimately lead to alternative pharmacotherapy. / AFRIKAANSE OPSOMMING: Obsessiewe kompulsiewe steuring (OKS) is `n ernstige, verswakkende psigiatriese steuring
waarvan die onderliggende molekulêre etiologie steeds onbekend is. Bewyse verkry vanuit
familiestudies het voorgestel dat OKS moontlik veroorsaak word deur `n komplekse interaksie
van omgewings en genetiese faktore.
Om die genetiese faktore te identifiseer wat OKS vatbaarheid veroorsaak, is `n hele aantal
genetiese assosiasie studies onderneem, wat teenstrydige resultate gelewer het. Wat meer is, die
grootste hoeveelheid van hierdie studies het gefokus op `n klein aantal kandidaatgene wat vir
komponente van die serotonien en dopamine neurotransmittor weë enkodeer. Dit is egter,
gebaseer op die kompleksiteit van die kliniese manifestasies wat waargeneem word in OKS, heel
moontlik dat die patogenisiteit van die siekte bemiddel word deur `n breër kompleks van
interverwante neurotransmittor sisteme en seintransduksie weë. Daar is dus `n behoefte na die
identifikasie en ondersoek van nuwe kandidaatgene.
Een metode om sulke nuwe OKS kandidaatgene te identifiseer, is deur die gebruik van bestaande
kennis oor siektes wat fenomenologiese ooreenkomste het met OKS, siektes wat makliker
geneties ontleed kan word deur koppelingsanalises en dierestudies. Genetiese lokusse vir sulke
versteurings, geïdentifiseer deur koppelingsanalises, het die potensiaal om nuwe OKS
kandidaatgene in te sluit, terwyl gene wat geïmpliseer word deur dierestudies mag lei tot die
identifisering van bykomende vatbaarheidsgene deur die ondersoek van weë deur, byvoorbeeld,
interaktoom analises. `n Voorbeeld van so `n versteuring is skisofrenie, wat in manifestasie
oorvleuel in beide simptome en breinstroombane met OKS. In skisofrenie het, addisioneel tot
verskeie geval-kontrole assosiasiestudies wat gedoen is, koppelingsdata, studies van
chromosomale afwykings en dierestudies gelei tot die identifikasie van verskeie chromosomale
gebiede wat gene mag bevat wat betrokke kan wees in die etiologie van die siekte, en dus ook
OKS kandidaatgene mag bevat.
In die huidige ondersoek is hierdie benadering gevolg en is gebruik gemaak van voorheen
gerapporteerde skisofrenie vatbaarheidslokusse om nuwe OKS kandidaatgene te identifiseer.
Alle gene wat in hierdie lokusse voorkom is gekatalogiseer en individueel geanaliseer deur
gebruik te maak van `n battery van bioinformatika tegnieke om hul potensiaal as kandidate vir
OKS vatbaarheid te bepaal. Hierdie analise het 13 geloofwaardige OKS kandidate opgelewer. Addisionele kandidate is gesoek deur inligting van `n goed gedefinieerde skisofrenie dieremodel
te gebruik, naamlik die heterosigotiese “reeler” muismodel, wat neuro-ontwikkelings-,
neuroanatomiese- en gedragsabnormaliteite vertoon, soortgelyk aan dié wat voorkom by pasiënte
met skisofrenie.
Die feit dat daar aangetoon is dat beide reelin protein en bRNS vlakke verlaag is in post-mortem
brein seksies van skisofrenie pasiënte, gekoppel aan die gedrags- en neurochemiese ooreenkomste
wat gesien word tussen heterosigotiese “reeler” muise en skisofrenie pasiënte, stel voor dat reelin
betrokke is by die patogenese van skisofrenie en dus ook OKS.
Vir hierdie rede is nuwe proteïene gesoek wat `n interaksie met reelin toon, deur gebruik te maak
van die N-terminale reeler-domein van reelin, `n domein wat slegs gevind word in proteïene wat
betrokke is by neuronale migrasie, as “aas” in `n gis-twee-hibried sifting van `n fetale brein cDNS
biblioteek. Vermeende reelin ligande is vervolgens herevalueer deur gebruik te maak van koimmunopresipitasie
en soogdier twee-hibried analises om die gis-twee-hibried bevindings te
bevestig. Resultate van hierdie analises het getoon dat daar interaksie is tussen WDR47, `n
WD40-herhalingsdomein protein, met reelin via sy reeler-domein. Die geen wat hierdie ligand
protein enkodeer, sowel as RELN self, is dus beskou as ‘n geloofwaardige OKS kandidaatgeen.
Elkeen van die kandidaatgene wat geïdentifiseer is deur gebruik te maak van bogenoemde
strategieë is ondersoek vir `n potensiële rol in die etiologie van OKS deur gebruik te maak van
geval-kontrole assosiasie studies met `n groep Afrikaner OKVS pasiënte en kontrole individue.
Statisties-betekenisvolle assosiasies met die versteuring is vasgestel vir twee gene, DLX6 en
SYN3. Hierdie assosiasies is opwindend aangesien hul nuwe meganismes betrokke by OKS
ontwikkeling mag aantoon.
Die identifikasie van WDR47 as ‘n nuwe protein wat interaksie met reelin vertoon, het
betekenisvolle implikasies vir die verstaan van reelin-afhanklike seining. Deur hierdie proteïn as
die beginpunt te gebruik kan vêrdere nuwe komponente van die reelin seinweg ontdek word, `n
ondersoek wat mag lei tot die identifisering van nuwe funksies vir reelin in neuro-ontwikkeling.
Sulke nuwe komponente mag, natuurlik, ook in aanmerking kom as OKS en skisofrenie
kandidaatgene, wat op sy beurt weer die bestaande kennis van die patofisiologie van OKS,
skisofrenie en ander neuro-ontwikkelings versteurings mag verbreed. In samevatting, hierdie studie het opwindende resultate gelewer wat opvolgondersoeke in die
toekoms regverdig. Die identifikasie van DLX6 en Syn3 as nuwe OKS vatbaarheidsgene, sowel
as die identifisering van WDR47 as ‘n protein wat interaksie vertoon met reelin, mag aan
navorsers alternatiewe navorsingsweë voorsien om die moontlike patologiese meganismes wat
betrokke is by beide OKS en skisofrenie te ondersoek, wat uiteindelik mag lei tot alternatiewe
farmakoterapie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/21666 |
| Date | 12 1900 |
| Creators | Kinnear, C. J. (Craig John) |
| Contributors | Moolman-Smook, Johanna C., Corfield, Valerie A., Emsley, Robin A., Stellenbosch University. Faculty of Health Sciences. Dept. of Biomedical Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xxv, 330 leaves : ill. |
| Rights | Stellenbosch University |
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