Objective: Diabetic nephropathy in type 1 diabetes is associated with familial aggregation of diabetes. In order to explore the mechanisms behind this association, we assessed glucose metabolism in glucose-intolerant relatives of type 1 diabetic patients with (ALB+) or without (ALB-) elevated urinary albumin excretion rate (UAER).
Methods: Glucose tolerance and insulin secretion were assessed using an oral glucose tolerance test (OGTT) and insulin sensitivity was measured with the short insulin tolerance test (ITT).
Results: One hundred and fourteen parents and siblings of 43 type 1 diabetic patients with ALB+ (UAER > or = 20 microg/min) were identified and 93 parents and siblings of 39 patients with ALB- (UAER < 20 microg/min). From this pool, a further selection was made of those (25 and 13 relatives of patients with ALB+ and ALB-, respectively) with mild abnormalities of glucose metabolism (fasting plasma glucose < 7.8 mmol/L; 2 h plasma glucose > or = 7.8 mmol/L in the OGTT). No difference in insulin sensitivity was discernible between the two groups of relatives (KITT 3.3 +/- 1.0 vs. 3.2 +/- 1.0%/min, p=NS). Although there were no significant differences in the incremental areas under glucose or insulin curves (AUC) between relatives of ALB+ and ALB- in the OGTT, the insulin secretory response to the rise in plasma glucose was impaired in relatives of patients with ALB+ (insulin AUC/glucose AUC: 7.1 [1.1-30.8] vs. 9.8 [3.6-52.2], p=0.039).
Conclusions: Glucose-intolerant relatives of patients with elevated UAER seem to be characterized by impaired insulin secretion. Genetic or environmental factors related to impaired insulin secretion may be important in the development of diabetic nephropathy.