Genetic epidemiology of NIDDM among Asian Indians.

Prevalence of non-insulin-dependent diabetes (NIDDM) in India was reported to be 2.3% in the urban and 1.5% in the rural areas in the early 1970s by the Indian Council of Medical Research (ICMR). Recent studies both in the migrant Indians and in the native Indians have shown the prevalence to be much higher than the above values. Similar prevalence of NIDDM in the migrant and native Indians in affluent areas suggests that Indians as an ethnic group have a high genetic risk for diabetes. Our recent study in South India showed a high prevalence of diabetes in the urban area (8.2%) versus a low prevalence of 2.4% in the rural area. Age, urban-rural factor, body mass index (BMI) and the waist:hip ratio (WHR) were positively associated with diabetes. Interestingly, the prevalence of impaired glucose tolerance (IGT) was similar in urban and rural areas (8.7% and 7.8%, respectively) despite a four-fold lower prevalence of diabetes in the latter. The ratio of new to known diabetes was 1:2 in the urban and 3:1 in the rural areas. There was a male preponderance among Indian diabetic patients. Migration from rural to urban environment with changes in dietary habits and physical inactivity may have contributed to the increased prevalence of diabetes. A high rate of familial aggregation is noted in NIDDM in India and the genetic risk of NIDDM increases with increasing family history of diabetes. In the adult offspring of diabetic parents, hyperinsulinaemia and decreased insulin sensitivity are observed before the development of glucose intolerance.