Abstract
A case with circulating glucagon binding antibody without any previous immunization was described. The patient was a 47-year-old married nurse. At the age of 44 (1977), a diagnosis of hyperthyroidism was made. Subsequently, she began to take methimazole (MMI). Four months of MMI treatment brought about a euthyroid state. She had no history of previous insulin or glucagon injection. The OGTT revealed a normal glucose tolerance. There was no circulating antibody to insulin or pancreatic polypeptide. The treponema pallidum hemagglutination test was negative.
Plasma immunoreactive glucagon could not be assayed in the native plasma taken in April, 1980 because there was a substance that strongly bound 125I-glucagon and interfered with glucagon radioimmunoassay. This binding substance was detected by the polyethylene glycol method. The value expressed as specific binding % was 13.2 (control=1.2). This high binding could be displaced only by porcine glucagon and porcine glicentin and became dissociated at acidic pH. The substance was found in the plasma protein fractions on gel filtration and proved to belong to γ-globulin (IgG, L-chain K-type) by means of salting out with ammonium sulfate and specific radioprecipitation.
The patient's history indicates that the glucagon binding antibody might have developed through autoimmunity. However, there were no clinical symptoms caused by the autoantibody.
Aside from the patient reported here, the glucagon binding antibody was detected in plasma samples of three patients with hyperthyroidism under MMI treatment out of 68 patients with thyroid disease (40: hyperthyroidism; 36: treated with MMI). These findings suggest that the development of glucagon binding antibody in hyperthyroidism may be associated with MMI treatment.
A few cases of hyperthyroidism treated with MMI and having insulin autoantibody have already been reported. However, this is the first report showing glucagon autoantibody.
