A study was made of 10 patients with simple goiter and a defect in deiodination of diiodotyrosine.

Six patients apparently had a defect both in thyroidal and in peripheral deiodination. All of them had an abnormally slow rate of deiodination of administered I131-labeled Ldiiodotyrosine (l-DIT I131). In vitro studies of the thyroid glands from 3 of these 6 revealed defective deiodination. The other 3 were goitrous cousins of one of them and presumably had a similar defect. The defective deiodination in these 6 patients persisted after thyroid treatment.

The other 4 patients had a defect in peripheral deiodination. All of them had an abnormality of deiodination of administered l-DIT I131. Thyroid tissue from 3 of these 4 was tested in vitro, and the deiodinating activity was found to be normal. The fourth was a goitrous daughter of one of them. This defect in peripheral deiodination seemed to be somewhat corrected by thyroid therapy.

Observations made on our patients suggest that a defect in deiodination of iodotyrosines in the periphery or throughout the body would be expected to produce simple goiter and that this defect is genetically determined.

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