South Asian Ancestry Raises Risk of Diabetes

People of Asian Indian ancestry are at increased risk for type 2 diabetes, even when they are thin, according to articles in the December 2003 and June 2004 issues of the Journal of Clinical Endocrinology and Metabolism. The researchers found that people of Indian, Pakistani, or Bangladeshi ancestry - all considered “Asian Indian” for these studies -a re metabolically and genetically different from those of European descent. (Traditionally, anthropologists have classified Asian Indians as “Caucasians.” In these studies, however, those descended from Europeans are referred to as “Caucasians”). Scientists already knew that insulin resistance and type 2 diabetes are common in India. The new research studied people living in the United States.
In the December 2003 study, the research team looked at whether two genes suspected to cause insulin resistance occur more often among people of Asian Indian ancestry than among Caucasians. They also investigated whether people who had these genes were more insulin-resistant than those who didn’t.
There were 738 subjects of European ancestry and 638 subjects of Asian Indian ancestry; some of the Asian Indians were recent immigrants, and others had been born in the United States. Genetic tests found that one of the two suspect genes, called PC-1 121 Q, occurred significantly more often in the Asian Indians. Blood tests also showed that Asian Indians with this gene were less insulin sensitive than Asian Indians without it. Among Caucasians, the gene did not affect insulin sensitivity in this study.
The researchers concluded that the PC-1 121Q gene is strongly associated with insulin resistance among Asian Indians in the United States. Because insulin resistance raises the risk of type 2 diabetes, people with this gene are likely more prone to diabetes. In the June 2004 study, the researchers compared insulin-resistant Asian Indian men with less-insulin-resistant Caucasian men. They sought to find out whether the men’s fat cells released similar amounts of leptin, adiponectin, and none sterified fatty acids (NEFA). (Obese people produce high levels of leptin and NEFA and low levels of adiponectin; these abnormalities may help cause the insulin resistance that often accompanies obesity.).
The Asian Indians’ higher levels of NEFA and leptin and lower levels of adiponectin suggest that the bodies of thin Asian Indians are metabolically similar in some ways to those of overweight Caucasians. The researchers concluded that Asian Indians may have a fat cell defect that makes them produce the wrong quantities of these three substances and so leads to insulin resistance, even when a person isn’t overweight. Insulin resistance, in turn, presumably leads to a higher risk of type 2 diabetes.
Together, these studies suggest that people of Asian Indian ancestry are genetically more prone to type 2 diabetes. Thus, it is extra important for people with such ancestry to stay as thin as possible, to exercise regularly, and to be aware of the symptoms of diabetes.

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Editor: Akhtar M. Faruqui
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