Thyroid stimulation—blocking antibody (TSBAb), an antibody that blocks stimulation of thyroid adenylate cyclase induced by thyrotropin stimulation,1 has been considered to play some pathogenetic role in atrophic autoimmune primary hypothyroidism.2,3 We describe a familial clustering of TSBAb that affected 4 members of 1 family. We believe that these cases provide a novel mechanism of hereditary hypothyroidism.
Report of Cases.
The proband, a 63-year-old woman, presented with general malaise and edema. Her goiter was not palpable. She was found to have hypothyroidism (free thyroxine, 4 pmol/L [0.3 ng/dL]; thyrotropin, 149 mU/L) and was positive for both thyrotropin receptor antibody (88.1%) and TSBAb (92.8%). Serologic tests were also positive for antithyroglobulin and antithyroid microsomal antibodies (X200 and X200). Her daughter, who had been diagnosed as having hypothyroidism with TSBAb (73.0%), had been treated with levothyroxine (100 μg/d) for several years. Her son had once been treated in another clinic under