A variant of iodotyrosine-dehalogenase deficiency

Three siblings (products of consanguineous marriage) affected with iodotyrosine-dehalogenase deficiency (presumed homozygotes) were found to have low thyroxine and large multinodular goiters, but none was mentally retarded. Iodide therapy corrected the serum T4 and thyroidal iodide uptake and discharge curve. The goiters shrank with iodide treatment. The subjects demonstrated significant ability to deiodinate intravenously injected L-mono-iodotyrosine (MIT) but not L-diiodotyrosine (DIT); 9.9% and 80.0% of an injected dose of 125I-MIT and 125I-DIT appeared unchanged in the urine 4 h, respectively. The data in presumed heterozygote subjects (both parents and two other siblings) were intermediate between controls and affected subjects. Thyroidal dehalogenase activity was measured in one of the affected subjects in vitro. The tissue showed greater ability to deiodinate MIT than DIT, but both activities were much lower than that of control tissue. The disease appears to be transmitted in an autosomal recessive fashion. The MIT-dehalogenase activity demonstrable in the affected individuals may explain the mild phenotype, in that MIT leaking from the goiter can be deiodinated to a significance degree and the liberated iodide reutilized.