Diabetes and Evolutionary Lag in the Sea Islanders
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Overview
abstract
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Rates of diabetes have increased dramatically over the course of recent human history. The reasons for this increase are not clear. Changes in food source and the nature of foods consumed has had profound impacts on the evolution of human physiology and morphology. There has been a pronounced trend towards increasing consumption of carbohydrates (particularly refined carbohydrates) over the course of human history, particularly in regions and cultures strongly influenced by western European civilization. Diabetes is a disease that is intimately associated with the control of glucose levels. There is increasing evidence that consumption of high levels of carbohydrate in the diet is associated with increased risk and earlier onset of diabetes. We propose that evolutionary lag is likely to have important effects with respect to observed disparities for diabetes. Specifically, populations with traditional cultures that have not emphasized or been exposed to high carbohydrate diets until quite recently in human history may be at higher risk for diabetes when exposed to the modern western diet and its associated high refined carbohydrate levels. Alleles of genes associated with various facets of carbohydrate physiology that predispose individuals to diabetes in the context of a high carbohydrate diet may be neutral or even beneficial in the context of a traditional diet that is comparatively low in carbohydrates. The African American population from the Sea Islands of coastal South Carolina and Georgia are a useful resource to interrogate our hypothesis. Type 2 diabetes and related metabolic disorders are common in the AA Sea Island population, with earlier age at onset of diabetes than AA from other studies. Moreover, the Sea Island AA population is a homogeneous population with low levels of admixture. We propose to carry out preliminary research by completing the following specific aims: (1) Evaluation of dietary differences: we will compare the traditional diet consumed in the native homeland of Sea Island AA (i.e. West Africa) with the American diet, by consulting ethnographic records from the regions and historical records that describe traditional dietary practices. (2) We will collect and organize a dataset of genomic data focused on loci that have been detected as risk alleles for Type 2 diabetes in African American (and especially Sea Islander) populations in previous research. (3) We will use recently developed evolutionary molecular genetic statistical methods implemented in computer software programs, to analyze the genomic data we collect for evidence of recent natural selection on these alleles, specifically in Sea Islander populations, as predicted by the hypothesis of evolutionary lag.
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