Doctoral Degrees (Chemical Pathology)

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Browsing Doctoral Degrees (Chemical Pathology) by Author "Vergotine, Zelda"

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    Molecular investigation of genetic factors associated with insulin resistance and obesity in a South African population
    (Stellenbosch : Stellenbosh University, 2015-12) Vergotine, Zelda; Erasmus, Rajiv T.; Matsha, Tandi E.; Pillay, Tahir S.; Kotze, Maritha J.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Pathology: Chemical Pathology.
    ENGLISH ABSTRACT: Background: The aetiopathogenesis of type 2 diabetes and the associated insulin resistance have been shown to have a strong genetic basis. Several genetic variants of the peroxisome proliferatoractivated receptor gamma (PPARG) and the insulin receptor substrate (IRS) 1 genes have been associated with the metabolic states of obesity, insulin resistance and type 2 diabetes in Caucasian populations. Furthermore, insulin resistance is strongly associated with diabetes and subsequent cardiovascular disease. These are increasingly common in low- to middle -income countries, including South Africa. Limited information is currently available regarding genetic associations with insulin resistance in African populations. Objectives: (1) To identify subjects with insulin resistance and determine the frequencies of the single nucleotide polymorphisms in the PPARG and IRS1 genes and examine the associated risk of insulin resistance and type 2 diabetes mellitus in a mixed-ancestry South African population. (2) To investigate the relationship between indices of insulin resistance and carotid intima media thickness, a marker of subclinical cardiovascular disease/atherosclerosis. Methods: A total of 856 (235 males) mixed-ancestry adults drawn from an urban community of Bellville South, Cape Town were genotyped for PPARG Pro12Ala (rs1801282, G>C), Pro115Gln (rs1800571, G>T), Val290Met (rs72551362, G>A), Pheu388Leu (rs72551363, T>A), Arg397Cys (rs72551364, C>T), His449His (rs3856806, C>T) and IRS1 Gly972Arg (rs 1801278, G>A). The oral glucose tolerance test was performed and cardiometabolic risk factors measured. Insulin resistance was estimated by the homeostasis model assessment of insulin resistance, the homeostasis model assessment of functional beta-cells, the quantitative insulin-sensitivity check index, the fasting insulin resistance index and the glucose/insulin ratio. Carotid intima media thickness was measured in longitudinal section at the far wall of the distal common carotid arteries, 2 cm from the bifurcation, at three consecutive end-points, 5-10 mm apart. Results: The genotype frequencies of PPARG Pro12Ala, IRS1 Gly972Arg and PPARG His449His were 10,4%, 7,7% and 23,8% respectively. No mutations were found for PPARG Pro115Gln, Val290Met, Pheu388Leu and Arg379Cys. In a model containing both PPARG Pro12Ala and IRS1 Gly972Arg alleles and their interaction term, the presence of the PPARG Pro12 resulted in a 64% risk of prevalent type 2 diabetes mellitus and was associated with higher 2 hour post-OGTT insulin levels in subjects with normoglycaemia. The PPARG Pro12 was associated with insulin resistance and interacted with IRS1 Gly972Arg, increasing the risk of type 2 diabetes mellitus. The PPARG His449His allele T frequency was about 14% and in an additive genetic model significantly reduced the risk of diabetes by 44%. After adjustment for age, gender, body mass index and diabetes status, the fasting plasma glucose (β=0,087;p=0,042) and glucose/insulin ratio (β=0,026; p=0,026) were associated with carotid intima media thickness. However, the effect on the overall model performance was marginal, R2<29,7%. Conclusion: The PPARG Pro12 was associated with insulin resistance and showed a gene-gene interaction with the unfavorable polymorphism IRS1 Gly972Arg, leading to an increased risk of type 2 diabetes mellitus. In contrast, the PPARG His449His T allele showed a protective effect against the risk of developing diabetes. Furthermore, indices of insulin resistance such as homeostatis model assessment of insulin resistance, quantitative insulin-sensitivity check index, fasting insulin resistance index and the glucose/insulin ratio were weakly associated with carotid intima media thickness in the risk stratification of cardiovascular disease in this population.