Nondiabetic, HLA-identical siblings of insulin-dependent diabetic subjects have an increased risk of developing diabetes. Since insulin resistance is present in newly diagnosed diabetic subjects, we studied 12 HLA-identical siblings to determine whether they have impaired insulin sensitivity. Each sibling was carefully matched for age, sex, and body weight to a control from a nondiabetic family. The insulin sensitivity index (S1,) was determined after an intravenous glucose tolerance test (IVGTT) using the minimal model of insulin kinetics. The insulin sensitivity index was significantly lower in the HLA-identical siblings compared with their matched controls.

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