Peripheral Metabolism of Thyroid Hormones in Congenital Thyroid Hormone Transport Abnormalities: Familial Dysalbuminemic Hyperthyroxinemia and TBG Increase
Familial dysalbuminemic hyperthyroxinemia (FDH) and inherited increase of thyroxine-binding globulin (TBG) in plasma are two very uncommon thyronine serum-binding protein abnormalities that cause hyperthyroxinemia without hyperthyroidism. In FDH, subjects have an abnormal albumin molecule which shows increased affinity only for thyroxine (T4). As a result, serum total T4 (TT4) value is increased, while the serum total triiodothyronine (TT3) concentration is normal or slightly elevated. Nevertheless, the increase in the free T4 index frequently leads to an erroneous diagnosis of thyrotoxicosis. On the contrary, in the inherited high TBG syndrome, proportionate increments in serum TT4 and TT3 concentrations are seen because TBG has a high affinity for T4, as well as T3, whereas the free T4 index remains normal.
KeywordsAffinity Constant Familial Dysalbuminemic Hyperthyroxinemia Serum Total Triiodothyronine Congenital Elevation Abnormal Serum Albumin
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