Genetics of Adiposity and Glucose Homeostasis

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The IRAS Family Study, initially funded as six linked R01s in 1999, is a multicenter project designed to study the genetic epidemiology of adiposity and glucose homeostasis. The recruitment and phenotyping components have been completed in the three clinical centers. All families were of African-American or Hispanic descent. A total of 132 extended families (1861 subjects) have been studied for measurement of adiposity by abdominal CT scan and glucose homeostasis using the insulin-modified frequently sampled intravenous glucose tolerance test (FSIGT). These investigations have identified substantial genetic contribution to measures of adiposity (visceral and sub-cutaneous fat, BMI and waist circumference) and glucose homeostasis (insulin sensitivity, glucose effectiveness, acute insulin response to glucose, disposition index, fasting glucose and fasting insulin). A 10 cM genome scan of the IRAS Family Study DNA has been completed. Linkage analyses have identified several genomic regions related to adiposity and glucose homeostasis. Several of these signals have been followed-up with fine mapping. This renewal application, entitled Genetics of Adiposity and Glucose Homeostasis, targets the further exploration of genomic regions and positional cloning of genes contributing to variation in adiposity and glucose homeostasis. Positional candidate genes will be identified. We will also re-contact the original cohort to repeat some of the primary phenotypes for measures of change (abdominal CT scan and fasting insulin) and add several important new phenotypes to add depth to our assessment of adiposity and glucose homeostasis (total body fat by DXA and adipocytokines, including adiponectin and soluble TNF-a receptors 1 and 2). A panel of nutritional, dietary, and eating behaviors will be assessed in which to study the genetic effects. Using the existing genome scan data and variance-components-based linkage analysis methods, regions of the genome will be detected that contribute to variation in these new phenotypes and in the change phenotypes. The proposed study is unique in its performance of gone discovery for adiposity and glucose homeostasis in a multi-ethnic (non-majority) sample while simultaneously examining the genetic and environmental correlations among these and other metabolic phenotypes.