Thesis (PhD (Biomedical Sciences. Molecular Biology and Human Genetics))--University of Stellenbosch, 2007. / The infectious disease tuberculosis (TB) is one of the leading causes of death
worldwide. The idea that infectious diseases are the most important driving force in
natural selection and that they sustain frequent polymorphisms in the human genome
was formally suggested by Haldane in 1949. This hypothesis implicated the human
genetic component in the response to infectious disease. Today the involvement of host
genetics in TB has been proven unequivocally and, together with environmental factors
(e.g. nutrition and crowding) and the causative bacterium, Mycobacterium tuberculosis
(M.tuberculosis), may influence the outcome of disease. As is evident, TB is a complex
disease and the implication for studying genetic susceptibility is that a number of genes
will be involved.
Interferon gamma (IFN-7) is the major macrophage-activating cytokine during infection
with M.tuberculosis and its role has been well established in animal models and in
humans. This cytokine is produced by activated T helper 1 (Th1) cells. These Th1
responses can best deal with intracellular pathogens such as M.tuberculosis. We
selected twelve candidate genes based on the hypothesis that genes which regulate the
production of IFN-7 may influence TB susceptibility. We also selected polymorphisms
from 27 other candidate genes, which may affect immunological pathways involved in
TB, to investigate as susceptibility factors based on the following hypotheses: 1)
granulomatous diseases can share susceptibility genes; 2) gene expression studies done
by DNA-array analysis experiments may reveal TB susceptibility genes; 3) genomewide
linkage studies in TB can determine susceptibility loci and genes in this region are
possibly susceptibility factors; and 4) functional susceptibility polymorphisms in genes
involved in immune-mediated diseases other than TB may contribute to susceptibility to
TB.
This research tested the association of 136 genetic polymorphisms in 39 potentially
important genes with TB in the South African Coloured population. Well-designed
case-control association studies were used and we attempted to replicate these findings
in an independent sample set using family-based case-control designs (transmission
disequilibrium tests (TDTs)). In addition, haplotypes and linkage disequilibrium (LD)
in the candidate genes were also investigated.
During the case-control analyses we found significant associations for 6 single
nucleotide polymorphisms (SNPs) in the following genes: SH2 domain protein 1A, tolllike
receptor 2, class II major histocompatibility complex transactivator, interleukin 1
receptor antagonist, runt-related transcription factor 1 and tumour necrosis factor
superfamily, member 1B. Discrepant results were obtained during the TDT analyses.
The number of families available was small and for this reason we cannot conclude that
the case-control results were spurious. We also tested the association of haplotypes
with TB. Haplotypes in the interleukin 12, beta (IL12B) and toll-like receptor 4 genes
were nominally associated with TB in both the case-control and TDT analyses. We
observed strong LD for the genes in the South African Coloured population. In total 17
novel SNPs were identified and one novel allele was found for a microsatellite in
IL12B.
This research contributes to the increasing amount of information available on genes
involved in TB susceptibility, which in the future may help to predict high risk
individuals.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/1264 |
| Date | 12 1900 |
| Creators | Moller, Marlo |
| Contributors | Hoal, Eileen, Van Helden, Paul, University of Stellenbosch. Faculty of Health Sciences. Dept. of Biomedical Sciences. Molecular Biology and Human Genetics. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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