Persistent infantile hypothyroidism attributable to thyroxine-binding globulin deficiency

An infant diagnosed with thyroid-binding globulin (TBG) deficiency after ne wborn screening demonstrated persistent elevation of thyroid-stimulating ho rmone (TSH) and abnormally low free thyroxine (fT4) levels. Treatment with thyroxine (T4) normalized fT4 and TSH levels during the first 5 years of li fe, but withdrawal of T4 supplementation at that time was associated with r eturn of hyperthyrotropinemic hypothyroidism. To our knowledge, this patien t is the first reported case of TBG deficiency-associated hypothyroidism. I n rare instances, TBG deficiency may lead to hypothyroidism requiring hormo ne supplementation.