Defective iodination of tyrosine a cause of nodular goiter?

Abstract

Twenty patients with colloid nodular goiter, 7 patients with Hashimoto's struma, and 15 patients without thyroid disease (all non-deaf) were tested with radioactive iodine and potassium thiocyanate for a thyroidal defect in iodination of tyrosine. In the cases of colloid nodular goiter with a family history of goiter there was a higher incidence and more severe degree of defective iodination of tyrosine than in the cases of colloid nodular goiter without a family history of goiter. Defective iodination of tyrosine was demonstrated in 1 sibling with proved colloid nodular goiter and in 1 with Hashimoto's struma. Iodination of tyrosine was impaired in 1 patient with her fourth recurrence of colloid nodular goiter. These data suggest that defective iodination of tyrosine is not uncommon in euthyroid non-deaf subjects with colloid nodular goiter, and may occur on a familial basis. ATRACER dose of radioactive iodine (I131) is normally incorporated into the tyrosine molecule shortly after entering the thyroid gland (1). If an oral dose of potassium thiocyanate (KSCN) is given to a person with a normal thyroid gland two hours after the administration of a tracer dose of I131, the resultant decrease in concentration differential for ionic iodide across the follicular cell membrane does not result in an exodus of I131 from the thyroid gland because the I131 already incorporated into the tyrosine molecule does not leave the follicular cell. If the process of iodination of tyrosine is impaired, however, nonorganified I131 leaves the thyroid gland after the administration of KSCN. Defects in the organification of iodine have been noted during administration of thiouracil (2), and in goitrous cretins (3), congenitally nerve-deaf siblings in whom goiter later developed (4), and patients with Hashimoto's struma (5).