Does hypoadiponectinemia explain the increased risk of diabetes and cardiovascular disease in South Asians?

A substantial body of evidence has documented the high prevalence of type 2 diabetes and cardiovascular disease (CVD) among people of SouthAsian descent, defined on the basis of ancestral origin from the Indian subcontinent comprised of India, Pakistan, Bangladesh, and Sri Lanka (1–7). These observations relate to both native South Asians in urban settings and those living overseas in different countries (including the U.K., Canada, the U.S., South Africa, Singapore, Fiji, and Trinidad), leading to the suggestion that members of this ethnic group may share an underlying predisposition to metabolic and vascular disease (3,4,6–10). It has been postulated that a gene-environment interaction between underlying genetic susceptibility and urbanization-induced lifestyle changes (such as increased caloric intake and decreased energy expenditure) may promote the clinical expression of a highrisk phenotype (7). Clinically, this phenomenon translates to a 1.5to 10-fold– higher incidence of coronary artery disease (CAD) in immigrant South Asians compared with the general populations of the host countries (2–4,10,11). Furthermore, South Asians exhibit clinical features suggestive of a distinctly aggressive cardiovascular pathophysiology compared with other ethnic groups. These features include significantly higher cardiovascular mortality (4,12) and earlier onset of CAD in young adults (7,13). Thus, identification of the determinants of vascular disease in South Asians may be relevant to both 1) our understanding of the pathophysiology of CVD and 2) preventive health care for the approximately one-fifth of the world’s population that comes from the Indian subcontinent. A similarly worrisome problem is the rising prevalence of type 2 diabetes in South Asians. India currently has the highest number of cases of diabetes in the world (14). In addition, it has been projected that between 2000 and 2030, the number of patients with diabetes in India will increase from 31.7 to 79.4 million, reflecting the highest national increase within the global diabetes epidemic (14). In the U.K., the prevalence of diabetes in people of South-Asian descent is as high as 16–20% (2,7,15). Furthermore, South Asians develop type 2 diabetes at an earlier age and at lower BMI than Caucasians (16). Even in the absence of overt diabetes, South Asians exhibit higher fasting glucose levels and more glucose intolerance than other ethnic groups (6). Thus, as with CVD, elucidation of the factors underlying abnormal glucose metabolism in South Asians is sorely needed.