Congenital nonautoimmune hyperthyroidism in a nonidentical twin caused by a sporadic germline mutation in the thyrotropin receptor gene

Congenital hyperthyroidism is usually caused by maternal-to-fetal transfer of thyroid-stimulating antibodies from a mother with autoimmune thyroid disease. Very recently, activating thyrotropin (TSH) receptor germline mutations were detected in a few patients with sporadic nonautoimmune congenital hyperthyroidism, as well as in familial forms of nonautoimmune hyperthyroidism defining a new pathophysiological entity of hyperthyroidism. In this report, we describe a nonidentical twin girl with severe congenital hyperthyroidism. The twin brother and the mother were euthyroid. Skull radiographs revealed premature synostosis of the sagittal sutures. Hyperthyroidism was inadequately controlled with antithyroid drugs and radioiodine therapy. After a near-total thyroidectomy performed at age 3, the patient became hypothyroid and required thyroid hormone replacement. At age 14, hyperthyroidism recurred. A hyperplastic remnant of the right upper lobe was removed surgically, resulting in euthyroidism. Over the follo...