A Case of Hypo-Responsiveness to Thyroid Hormone

A 16-month-old male patient with severe growth and mental retardation is reported. Although his thyroid function tests showed high circulating levels of free 3, 5, 3′-triiodothyronine (T3), free thyroxin (T4) and thyrotropin (TSH), he had no clinical manifestations suggesting hyperthyroidism. Physical responses to exogenous T3 were normal. T4 supplement (7-10μg/kg/day) dramatically improved his growth and mental development, suggesting that his clinical symptoms were due to a relative shortage of thyroid hormone. Direct sequencing confirmed that he carried a normal thyroid hormone receptor β (TRβ) gene. The mechanism causing hypo-responsiveness to thyroid hormone in this patient is unclear.