Evaluation of Pituitary and Peripheral Tissue Markers of Thyroid Hormone Action in an Iranian Family With Resistance to Thyroid Hormone

Resistance to thyroid hormone (RTH), an inherited syndrome of reduced sensitivity to thyroid hormone, is being detected with increased frequency. We report the first family with RTH identified in Iran. Goiter prompted thyroid evaluation, and nonsuppressed TSH associated with high free T₄, suggested RTH as the etiology. The mother and all four of her children expressed the RTH phenotype associated with attention deficit and hyperactivity. Detailed clinical and laboratory studies before and following the administration of graded doses of L-T₃ demonstrated relatively severe resistance to the hormone at the level of the thyrotrophs and peripheral tissues. Our data underscore the importance of evaluating the changes of various parameters of thyroid hormone action in response to thyroid hormone rather than their measurement at baseline or assessment of absolute levels.