The syndromes of reduced sensitivity to thyroid hormone

► Defects of TH action manifest as tissue and cell specific TH deficiency and excess. ► The syndrome of resistance to TH has helped elucidate the mechanism of TH action. ► Neurological deficits of MCT8 defects are more severe than in congenital hypothyroidism. ► SBP2 defects reduce selenoprotein synthesis and alter intracellular TH metabolism.