Increase in thyroxine-binding globulin (TBG) in lysinuric protein intolerance

The common occurrence of increased serum PBI concentration in patients with lysinuric protein intolerance (LPI) was elucidated by further studies. The reason was found to be an increase in the concentration of thyroid binding globulin (TBG), concomitantly with an increase in the binding capacity of TBG. The concentrations of serum thyroxine and triiodothyronine were elevated, whereas the free thyroxine index remained normal. The free triiodothyronine index was slightly increased. The binding capacity of thyroid hormone binding pre-albumin (TBPA) was significantly decreased. The concentrations of reverse triiodothyronine (3,3',5'-T3) and of 3,3'-diiodothyronine were normal. In all patients serum lactic acid dehydrogenase activities and ferritin concentrations were elevated. The reason for the almost constant increase in TBG remains obscure. It may be related to the primary disorder of LPI, a defect in diaminoacid transport.