[Familial increase in thyroxine binding globulins in the blood]

Elevation of Thyroxine-binding globulin (TBG) in serum may lead to abnormally high total-thyroxine (T4) concentration. Causally hyper-TBG-aemia can either be acquired (estrogentherapy; hepatitis etc.) or familial. In a family-study with 3 generations 6 persons were found with this rare anomaly. Analysis of the pedigree is in accordance with an X-chromosomal transmission. Five of the affected family members were clinically euthyroid and had normal T4/TBG and effective thyroxine ratios (ETR). In one patient hypothyroidism was detected by these indirect parameters despite a normal T4-concentration. Changes in serum levels of thyroxine binding proteins make it difficult to diagnose a disturbance in thyroid function. However indirect parameters for free T4 (ETR, T4/TBG) as well as the TRH-Test allow a clear diagnosis in such patients.