The Iodoproteins in the Iodotyrosyl Coupling Defect

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Abstract
A euthyroid child with a large goiter demonstrated the diagnostic criteria for the iodotyrosyl coupling defect. In spite of the presence of small amounts of thyroxine and T3 in the peripheral and thyroid vein serum, neither was found in thyroid gland hydrolysate. DIT and MIT were present in the gland in normal proportions. Almost all the 131I accumulated by the gland was incorporated into a protein molecule which migrated as albumin by starch-gel and paper electrophoresis. Salting out with ammonium sulfate likewise indicated the presence of a labeled protein with solubility greater than normal thyroglobulin. Rabbits immunized with saline extracts from the patient's thyroid produced circulating antibodies to both human thyroglobulin and serum albumin. It is suggested that the iodotyrosyl coupling defect may represent a heterogeneous group of disorders including defects in specific enzyme systems, subtle changes in the steric configuration of the thyroglobulin molecule, or synthesis of “thyroalbumin” in place of or at the expense of thyroglobulin.