Congenital Goiter with Iodoalbumin Replacing Thyroglobulin and Defect of Deiodination of Iodotyrosines. Serum Origin of the Thyroid Iodoalbumin

Abstract

The thyroid of an 8-yr-old girl with a congenital goiter without hypothyroidism has been studied. She presented the same biochemical symptoms as her brother, whose goiter was studied previously (J Clin Endocr27: 185, 1967). Iodinated serum proteins, of which an iodinated iodothyronine-containing serum albumin was the major component, were the predominant soluble iodinated proteins of the goiter. Poorly iodinated thyroglobulin accounted for only around 10% of total goiter iodoproteins. Qualitative and quantitative immunoprecipitation tests performed on the total soluble 14C-proteins synthesized during in vitro incubation of goiter slices in the presence of 14C-aminoacids failed to show the synthesis of 14C-serum albumin. A lack of DIT-deiodinating activity of the thyroid tissue in vitro has also been demonstrated: this defect explained the presence of free iodotyrosines in blood and urine. In this type of familial goiter, which combines 2 abnormalities (decrease or absence of thyroglobulin synthesis and defect of iodotyrosine-deiodinating activity), the hyperplastic thyroid gland synthesizes variable quantities of thyroid hormone by iodinating serum proteins (essentially serum albumin) picked up from the blood. Iodinated serum albumin is most probably a normal component of the thyroid and might, in hyperplastic glands associated with a congenital defect, become the predominant substrate for iodination and thyroid hormone formation. It is suggested that certain of the abnormalities observed (high T3:T4 ratio in the blood, presence of iodinated plasma proteins in thyroid and blood, decreased thyroglobulin synthesis) may be secondary to a unique primary defect, the lack of iodotyrosine-dehalogenase activity.