Absence of thyroid-stimulating antibody and long acting thyroid stimulator in relatives of Graves' disease patients.

None of the 76 euthyroid relatives of patients with Graves' disease had detectable LATS in their serum nor was thyroid-stimulating antibody (TSAb), assessed by an increment of cAMP in human thyroid slices, detected in any of the 60 sera tested. Seven of 41 were slightly positive for TSH binding-inhibiting immunoglobulin (TBII). Nineteen of 73 sera were positive (greater than 1:1600) for antibody to thyroid antimicrosomal antigen, of which 4 were also positive (greater than 1:400) for antibody to thyroglobulin; 3 of the 19 had a slightly elevated basal TSH which rose excessively after TRH. Thus, although these euthyroid relatives had evidence of thyroid immunological defects, a thyroid-stimulating antibody was not found.