Cardiovascular risk in Gullah African Americans with high familial risk of type 2 diabetes mellitus: project SuGAR.

Diabetes mellitus disproportionately affects minority populations, with African Americans having a two- to threefold increased risk, an earlier age of onset, and greater years of life lost than whites.1 For African Americans born in 2000 in the United States, the lifetime risk of developing type 2 diabetes mellitus was estimated to be 40.2% (95% confidence interval [CI] 36.1–44.7) in men and 49.0% (95% CI 44.6–53.7) in women.1 With projections of nearly one of every two African American women and two of every five African American men developing diabetes mellitus, it is imperative that we have a greater understanding of the causes and consequences of this disease in African American. Ancestral or ethnic differences in cardiometabolic risk factors are well documented, with hypertension and diabetes mellitus being more common and less controlled in African Americans than whites; however, African Americans have more favorable lipid profiles than whites.2–13 The literature documenting racial differences in metabolism, particularly between African Americans and whites, is extensive. For example, the Pro12Ala variant in peroxisome proliferator–activated receptor-γ2 has been associated with diabetes and has different allele frequencies depending on racial group.14,15 Documented racial differences in metabolism include greater insulin resistance, lower resting energy expenditure, greater abdominal subcutaneous fat but decreased visceral fat, lower adiponectin levels, and insulin hypersecretion independent of ambient insulin sensitivity in African Americans compared with whites.5–7,11,16 Although African Americans tend to be more insulin resistant,13 lipid profile clusters are distinct from those of whites.2,3 One analysis showed that low high-density lipoprotein (HDL) cholesterol and normal triglycerides levels were the most common pattern in both African Americans and Africans from Ghana and Nigeria with the metabolic syndrome.17 Admixture analyses have shown significant positive correlations between African ancestry and HDL cholesterol and European ancestry and triglycerides, but found no correlation with low-density lipoprotein (LDL) cholesterol.18,19 Furthermore, studies indicate that the metabolic syndrome, recognized as a cluster of cardiovascular risk factors that frequently coincide with insulin resistance and hyperglycemia,20,21 may differentially affect cardiovascular risk in African Americans and whites.17,22 African Americans living in coastal communities and on the Sea Islands of South Carolina are referred to as Gullah. These individuals are believed to be direct descendants of enslaved Africans who were deported from the “rice or windward” coast of west Africa and transported to the South Carolina Sea Islands because their rice-growing expertise was critical to the culture of this cash crop in colonial America. The Gullah population is unique because of its geographical isolation, cultural identity, large, stable multigenerational families, relatively uniform diet and lifestyle, low levels of genetic admixture, and high relative ancestral homogeneity. Moreover, although no formal population-based epidemiologic studies have been completed in Gullah African Americans, the prevalence of obesity, hypertension, and type 2 diabetes mellitus is perceived to be high in this population. From 1995 through 2003, the Sea Islands Genetic African American Registry (Project SuGAR) recruited Gullah African Americans from families on the South Carolina Sea Islands with a high prevalence of diabetes mellitus.23–26 The objectives of Project SuGAR were twofold and encompassed science as well as service. With respect to science, the aim was to study the genetic architecture of diabetes mellitus in the Gullah population, with the hypotheses being that ancestral differences exist in the pathophysiology of the metabolic syndrome and that the increased risk of diabetes mellitus in African Americans has a genetic basis. With respect to service, the aim was to provide free health education and disease screenings, health fairs, and referrals to this underserved community. The objective of this article was to describe the Project SuGAR study population and the phenotypic information collected as it pertains to cardiometabolic risk and preventive care in Gullah African Americans with a high familial risk of type 2 diabetes mellitus.