Browsing by Author "McGregor, Nathaniel Wade"
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- ItemCharacterization of the promoter region of the HAMP gene implicated in iron metabolism and its possible association with Oesophageal cancer in the black South African population(Stellenbosch : University of Stellenbosch, 2009-12) McGregor, Nathaniel Wade; Zaahl, M. G.; Warnich, L.; Louw, A.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Genetics.ENGLISH ABSTRACT: Oesophageal cancer (OC) is the sixth leading cause of cancer related deaths in the world with approximately 300 000 new cases reported each year. OC may be characterized into two forms with 90% of cases presenting as squamous-cell carcinoma (SCC) and the remaining 10% as adenocarcinoma (ADC). Several factors have been attributed to the development of OC, including oesphageal injury and/or irritation, chronic inflammation and excess iron associated with enhanced tumour growth. The HAMP gene codes for a 25 amino-acid protein found to be primarily expressed in the liver and crucial to regulation of bodily iron status. Defects occurring in the HAMP gene could therefore lead to the dysregulation of the gene, resulting in an iron overload status. Iron overload is a previously described risk factor in the development of various cancers, including OC, and therefore the aim of this study was to investigate whether dysregulation of the HAMP gene may be involved in the cancer phenotype exhibition. The study cohort comprised of 48 unrelated patients presenting with SCC and a control group of 51 healthy, unrelated population-matched individuals. Mutation detection techniques included polymerase chain reaction (PCR) amplification, heteroduplex single-stranded conformation polymorphism (HEX-SSCP) analysis and bi-directional semi-automated DNA sequencing analysis. Screening of the 5’ regulatory region (5’UTR) of the HAMP gene revealed one known (-582A/G) and two novel (-188C/T and -429G/T) variants with the -429G/T variant showing statistically significant reduction in expression in patients relative to controls. Iron parameters were correlated between patient and control cohorts, as well as for variant presence and absence within individuals. Luciferase reporter constructs were used to investigate the functional implications of the presence of a variant on HAMP gene expression, and how these results correlated to the iron parameter statistics obtained. Luciferase reporter assay results indicated the -188C/T and -429G/T variants to result in under-, and the -582A/G variant to result in over-expression at the basal level, relative to the respective wild-type sequence constructs. Correlation of the luciferase data with the iron parameter statistics, indicate the -429G/T variant to be coupled to significantly higher levels of ferritin and C-reactive protein (CRP) and significantly lower levels of serum-iron and transferrin when compared to individuals without the variant. Considering only the patient group, the presence of the -188C/T and -429G/T variants were coupled to significantly lower levels of transferrin in patients with either variant, compared to patients without. The variants found within the HAMP promoter region are therefore able to alter gene regulation to an extent where iron parameters deviate between healthy and OC afflicted individuals, and also between patients with and without a variant. This dysregulation in iron homeostasis may play a role in the development and/ or progression of OC. Characterisation of the 5’ UTR of the HAMP gene may contribute to linking iron regulation to the establishment of an effective screening program, facilitating the early detection of OC.
- ItemThe identification of novel susceptibility genes involved in anxiety disorders(Stellenbosch : Stellenbosch University, 2014-12) McGregor, Nathaniel Wade; Lochner, Christine; Hemmings, Sian; Kinnear, Craig; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Psychiatry.ENGLISH ABSTRACT: The etiology of anxiety disorders remains incompletely understood. Clear evidence for a genetic component has been proposed; however, there is also an increasing focus on environmental factors and the interaction between these and the genetic components that may mediate (anxiety) disorder pathogenesis. No single gene or genetic component has been explicitly identified as being involved in the development of anxiety disorders. This is most likely due to a number of reasons, which include, for example, the heterogeneity of anxiety disorders, the contribution of environmental factors and methodological limitations (e.g. small sample size) of research studies. Until now, genetic association studies usually focused on one particular psychiatric disorder at a time. However, with the difficulty in identifying susceptibility genes and/or loci in heterogeneous disorders like obsessive-compulsive disorder and other conditions in the anxiety spectrum, it is perhaps timely to consider multivariate genetics and epidemiological studies in a number of disorders sharing a core characteristic – such as anxiety. In addition to genetic underpinnings, a number of environmental variables have also been identified as risk factors for pathological anxiety, including adverse life events like childhood physical and sexual abuse. The hypothesis for this project is that a pre-existing genetic vulnerability (or genetic risk) interacts with the impact of adverse life events to result in the development of one or more anxiety disorder(s). Considering phenotypic overlap amongst the anxiety disorders, it is likely that diverse networks of genes and/ or interacting pathways are responsible for the phenotypic manifestations observed. Sprague Dawley rats exhibiting behaviours indicative of anxiety in the context of environmental stressors (maternal separation and restraint stress) were used as model for the identification of novel susceptibility genes for anxiety disorders in humans. The striatum has previously been implicated as a candidate in the brain architecture of anxiety pathogenicity, and is also a site exhibiting a high degree of synaptic plasticity. The synaptic plasticity pathway was investigated using the dorsal striatum of the rat brain and several genes were identified to be aberrantly expressed in “anxious” rats relative to controls (Mmp9, Bdnf, Ntf4, Egr2, Egr4, Grm2 and Arc). In humans, it was found that the severity of early adversity was significantly and positively associated with the presence of an anxiety disorder in adulthood. When the human homologues of the susceptibility candidate genes that were identified using the animal model were screened in a human cohort of patients with obsessive-compulsive disorder (OCD), panic disorder (PD) or social anxiety disorder (SAD) (relative to controls), five single nucleotide polymorphisms (SNPs) were found to be significantly associated with these conditions. Four of these SNPs were also found to significantly interact with the severity of childhood trauma. Haplotype analysis of variants within the identified susceptibility candidates revealed novel haplotype associations, four of which are located in the MMP9 gene. Notably, this the first study to link these particular mutations in the MMP9 gene with anxiety disorders and this finding is consistent with previous work suggesting that MMP9 is involved in conditions like cardiovascular disease and cancer which have been associated with increased prevalence of anxiety disorders. In conclusion, this project yielded important findings pertaining to the etiology of anxiety disorders. The use of a combined anxiety disorders cohort (OCD, PD and SAD) may suggest that the associations found here may hold true for anxiety disorders in general and not only for a particular clinically delineated condition. Childhood trauma was confirmed as an increased susceptibility risk for anxiety disorders. Also, this research contributed several novel susceptibility genes (MMP9, EGR2, EGR4, NTF4, and ARC), five significant SNP associations, four significant SNP-environment interactions and five haplotype associations (within MMP9 and BDNF) as candidates for anxiety pathogenicity. The identified polymorphisms and haplotypes were demonstrated to be associated with susceptibility to anxiety disorders in a gene-environment correlation and gene-environment interaction.
- ItemThe potential role of regulatory genes (DNMT3A, HDAC5, and HDAC9) in antipsychotic treatment response in South African schizophrenia patients(Frontiers Media, 2019-10-07) O’Connell, Kevin Sean; McGregor, Nathaniel Wade; Emsley, Robin A.; Seedat, Soraya; Warnich, LouiseENGLISH ABSTRACT: Despite advances in pharmacogenetics, the majority of heritability for treatment response cannot be explained by common variation, suggesting that factors such as epigenetics may play a key role. Regulatory genes, such as those involved in DNA methylation and transcriptional repression, are therefore excellent candidates for investigating antipsychotic treatment response. This study explored the differential expression of regulatory genes between patients with schizophrenia (chronic and antipsychotic-naïve first-episode patients) and healthy controls in order to identify candidate genes for association with antipsychotic treatment response. Seven candidate differentially expressed genes were identified, and four variants within these genes were found to be significantly associated with treatment response (DNMT3A rs2304429, HDAC5 rs11079983, and HDAC9 rs1178119 and rs11764843). Further analyses revealed that two of these variants (rs2304429 and rs11079983) are predicted to alter the expression of specific genes (DNMT3A, ASB16, and ASB16-AS1) in brain regions previously implicated in schizophrenia and treatment response. These results may aid in the development of biomarkers for antipsychotic treatment response, as well as novel drug targets.