DISSOCIATED THYROXINE, TRIIODOTHYRONINE AND REVERSE TRIIODOTHYRONINE LEVELS IN PATIENTS WITH FAMILIAL GOITRE DUE TO IODIDE ORGANIFICATION DEFECTS

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Abstract
The thyroid function of patients with 3 different types of organification defect was studied. All patients were characterized by a high thyroidal 131I uptake and a positive perchlorate discharge. Patients with Pendred''s syndrome who had goiter and congenital nerve deafness were mostly euthyroid with normal circulating thyroid hormone levels. Only 2 of them had compensated euthyroidism with elevated total T3 [triiodothyronine], high basal TSH [thyrotropin] and delayed return to basal value after TRH [thyroliberin]. The patients who were euthyroid with large goiters and normal hearing had elevated total T3 and an exaggerated TSH response to TRH. The thyroid function of these 2 groups of patients contrasted with that of goitrous cretins, who were clinically hypothyroid with low circulating total T4 [thyroxine], increased T3 and decreased r[reverse]T3 levels. In patients with intrathyroidal I deficiency secondary to organification defect, there is preferential T3 production in an effort to maintain euthyroid state; this is further substantiated in the case of gross thyroid insufficiency either by enhanced peripheral conversion of T4 to T3, or reduced metabolic clearance of T3 and increased clearance of rT3, resulting in elevated T3 and decreased rT3 levels.