Pituitary-thyroid function in Pendred's syndrome.

Pendred's syndrome is reported in three siblings. All were euthyroid, with large goitres and deaf mutism and all had an unusual deposition of pigment in the retina. All had raised circulating levels of triiodothyronine (T-3) and an exaggerated response of thyroid-stimulating hormone (TSH) to thyrotrophin-releasing hormone (TRH). It appears that their compensated euthyroid state was maintained by the raised T-3 levels. We suggest that preferential T-3 production is maintained by increased TSH secretion in subjects with intrathyroidal iodine deficiency secondary to thyroid organification defect.