Abstract
We report a case of familial insulin resistance due to a post-binding defect in insulin action, the type C syndrome of insulin receptor diseases. The patient was a 16-year-old girl with acanthosis nigricans and hyperinsulinemia. Hirsutism and polycystic ovary syndrome were absent. She had normal glucose tolerance as shown by a 100g oral glucose tolerance test, but her plasma insulin level was 40μU/ml at fasting and was as high as 746μU/ml during OGTT. She showed a blunted hypoglycemic response to an injection of 0.1U/kg exogenous insulin, indicating the presence of insulin resistance. Anti-insulin antibodies and anti-insulin receptor antibodies were not detected. Insulinbinding to erythrocytes was nearly normal. There was no proinsulin-like component in plasma by gel filtration with Biogel P-30. Plasma insulin was purified by affinity chromatography using anti-insulin serum. Only one peak of normal human insulin was detected by HPLC analysis. The patient's insulin competed normally with 125I-insulin for binding to insulin receptors from plasma membrane of guinea pig kidney, and exhibited a normal biological potency for stimulation of glucose oxidation of rat adipocytes. Her mother and two brothers also had hyperinsulinemia at fasting and after oral glucose load. The findings indicate that the patient's insulin resistance was due to a postbinding defect that was probably genetic in nature.
