FAMILIAL PARTIAL PERIPHERAL RESISTANCE TO THYROID HORMONES

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Abstract
A male aged 21 had elevated serum PBI [protein bound iodine] on several occasions. Further studies revealed clinical euthyroidism with raised serum concentrations of T4 [thyroxine], T3 [triiodothyronine] and free T4 with normal hormone binding capacity of the T4 binding proteins and normal thyroid-pituitary relationships. The response to TRH [thyrotropin releasing hormone] was high normal or on 1 occasion exaggerated. The extrathyroidal T4 pool and the daily turnover of thyroxine were considerably above the upper limit of the normal. The subject had no goiter. These findings indicated partial peripheral resistance to thyroid hormones including the pituitary gland. There were no circulating antibodies to thyroglobulin, thyroid microsomes, T4 or T3. A study of the propositus'' family revealed an autosomal dominant heredity of this abnormality. Similar findings were found in the brother, mother and the 2 uncles of the propositus. In these subjects the serum concentrations of T4, T3 and free T4 and that of r[reverse]T3 were raised above the normal. The subjects studied were clinically euthyroid. Goiter was present only in the older members of the family. The response to TRH was usually high normal or at times exaggerated and the basal TSH [thyrotropin] level seemed to fluctuate during years of follow-up indicating a continuous adjustment of the thyroid function by means of TSH secretion. The mother and the older uncle had previously been treated because of hyperthyroidism. Only the mother had circulating thyroid antibodies and none of the family members had antibodies against T4 or T3. This hereditary condition seems to have a very mild clinical manifestation in this family.