Decreased binding of insulin to erythrocytes in myotonic dystrophy

Recent several studies have shown that the insulin resistance exists in patients with myotonic dystrophy. Using in vitro radioreceptor assay with 125I-labeled insulin, we evaluated the binding of insulin to erythrocytes in patients with myotonic dystrophy. It was found that there was a decreased binding of insulin to erythrocytes in the patients with myotonic dystrophy. On quantitative analysis, this decrease in binding was found to be the result of a decrease in receptor affinity rather than receptor concentration. There was no evidence that the alteration in insulin receptor affinity was due to hyperinsulinemia. All of 7 patients with myotonic dystrophy also were shown to have an excessive response of endogenous insulin to a glucose challenge. No circulating antibody to insulin was found. These data suggest that a decrease in affinity of insulin receptors may, in part, cause insulin resistance and a compensatory elevation of the plasma insulin concentration in patients with myotonic dystrophy.