Congenital hypothyroidism in two cats due to defective organification: data suggesting loosely anchored thyroperoxidase.

Two cats with congenital hypothyroidism are described. In vivo discharge of accumulated labelled iodide by perchlorate administration revealed defective organification of iodide, which was complete in one cat and partial in the other. In the cat with the partial organification defect, thyroid tissue was obtained for biochemical studies. No membrane-bound peroxidase activity could be demonstrated. The activity was found in the 100,000 x g supernatant. It is suggested that the loose enzyme anchoring caused decreased availability of peroxidase and as a consequence reduced capacity for organic binding of trapped iodide.