Heterogeneity of insulin response in relatives of type-I and type-II diabetics

In 30 first-degree relatives (siblings or children) of type-I diabetics and 17 relatives (children) of type-II diabetics as well as in 19 healthy subjects a two-hour glucose infusion test (GIT, 12 mg/kg b.w./min) primed by a starting bolus of 0.33 g/kg b.w. was performed to evaluate carbohydrate tolerance (CHT) and insulin secretion pattern. After 4 to 5 years the test was repeated and the results were compared with those of the initial GIT. The glucose-stimulated insulin response of the early secretion phase (0--5 min) decreased during the follow-up study in relatives of type-II diabetics with normal CHT (in tendency) and with glucose intolerance (p less than 0.05) but not in relatives of type-I diabetics. A rightward shift of the glucose-insulin response curve was seen in the former group. Relatives of type-II diabetics with impaired CHT showed a striking abnormality in B-cell responsiveness. In relatives of type-I diabetics a disturbed glucose-insulin response curve could not be observed. The insulin response during the late phase of insulin secretion did not differ significantly among the groups. The conclusion drawn from our findings is that responsiveness of pancreatic B-cells seems to be directly affected genetically in first-degree relatives of type-II but not of type-I diabetics. Thus, diabetes mellitus cannot be regarded as one disorder with a similar genetic background.