The purpose of the study is to determine the role of beta-cell function and insulin resistance in the development of impaired glucose tolerance (IGT) and type 2 diabetes in children and adolescents who have an increased risk of developing type 2 diabetes due to overweight/obesity or a family history of overweight/obesity, diabetes and/or impaired fasting glucose. It is hypothesized that: 1)Obese adolescents with IGT will be more insulin resistant than obese adolescents with NGT. Insulin resistance will be the best predictor of changes in glucose tolerance status., 2)Beta cell function will be impaired in obese adolescents with IGT compared to obese adolescents with NGT., 3)Obese adolescents with IGT will present with greater intramyocellular, intrahepatic and visceral fat than obese adolescents with NGT. Furthermore, obese adolescents with IGT will have larger adipocytes, while having significantly fewer adipocytes compared to obese adolescents with NGT. Obese adolescents with IGT will also have altered expression of key genes related to insulin resistance., and 4)Abnormalities in endothelial function as manifested by low FMD and PAT are already present in obese adolescents with IGT and are linked to insulin resistance.
Impaired Glucose Tolerance
Type 2 diabetes is a serious and common chronic disease affecting an estimated 6.6% of the U.S. population 20 to 74 years of age. Among children, type 2 diabetes has previously been reported to account for 2% to 3% of all patients with diabetes mellitus. Recent studies, however, indicate that the prevalence of this disorder is increasing in the pediatric population. This phenomenon parallels the increased prevalence of obesity in children and adolescents, particularly in African-American and Hispanic ethnic groups. Despite the wealth of knowledge concerning the epidemiology, pathophysiology and treatment of type 2 diabetes in adults, we know little about the disease in children.Paralleling the rise in childhood obesity and type 2 diabetes is an increase in the metabolic syndrome in youth. The metabolic syndrome, also known as "Syndrome X," is characterized by hypertension, type 2 diabetes, dyslipidemia and obesity. This syndrome was first described in 1966 by Camus and again by Reaven in 1988. Cook et al. showed that the metabolic syndrome is already present in 6.8% of 12-19 year-olds with a BMI between the 85th and 95th percentiles, and in 28.7% of those with a BMI greater than the 95th percentile. In addition, recent studies from our group suggest that risk factors for type 2 diabetes and the metabolic syndrome are already present in overweight children and adolescents. As the degree of obesity worsens, the prevalence of these risk factors greatly increase.Overweight and obese adolescents with NGT and with IGT will be recruited. Progression from NGT to IGT and from IGT to type 2 diabetes will be assessed by annual oral glucose tolerance tests (OGTT). Comprehensive metabolic assessments will be employed to examine within and between group differences in insulin action and beta-cell function at baseline and during the follow-up.