A FAMILY WITH HEREDITARY HIGH SERUM THYROXINE-BINDING GLOBULIN

A family with hereditary high serum thyroxine-binding globulin was stu died. All the subjects studied were clinically euthyroid without goite r. The propositus (female), her mother and sister had high TBG, total T-4 and total T-3 with normal free T-4, free T-3 and TSH. Her father's thyroid function was within the normal range. Possible etiologic fact ors causing secondary hyper-TBG-nemia were ruled out in all the affect ed subjects. Isoelectric focusing demonstrated qualitatively normal mi croheterogeneity, ruling out possible TBG variations caused by liver d iseases, estrogen therapy or pregnancy. Although the mechanism involve d in the TBG increase awaits further investigation, it could be an abn ormality in the gene controlling the synthesis of TBG.