The influence of the plasma inorganic iodine concentration on thyroid function in dehalogenase deficiency

Iodine metabolism and thyroid function were studied in a patient with hypothyroidism and goitre due to dehalogenase deficiency. Initially the plasma inorganic iodine (PII) level was within the normal range but circulating levels of hormone were low and the thyroid clearance and absolute uptake of iodine (AIU) by the thyroid were high.

Administration of iodide supplements resulted in a rapid rise in the plasma thyroxine concentration and restoration of the euthyroid state. Thyroid hormone synthesis appeared to proceed normally when the PII exceeded 1.0 μg/100 ml. This was achieved by increasing the intake of iodide by 612 μg per day. At PII levels around 10 μg/100 ml there was evidence of increased levels of circulating thyroid hormone.

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Iodine excretion in urine, saliva, gastric juice and sweat in dehalogenase deficiency

The excretion of iodine in urine, saliva, gastric juice and sweat has been studied by using 131I-labelled monoiodotyrosine in a patient with the dehalogenase type of dyshormonogenesis. Iodinated components 'x', iodide, monoiodotyrosine and 'y' were found in the urine. A previously undescribed component (compound 'u') accounted for a large fraction of the urinary radioactive iodine. Organic iodinated compounds were not excreted in the saliva. Only inorganic iodide was found in the gastric juice. No organic iodine was detected in the sweat. The plasma inorganic iodine (PII) derived from salivary iodine measurements gave low values indicative of iodine deficiency. The PII values obtained from the urinary iodine were falsely high due to the presence of organic iodinated compounds.