INHERITANCE OF DECREASED THYROXINE-BINDING BY THE THYROXINE-BINDING GLOBULIN.

Abstract

Near absence of the thyroxinebinding by serum thyroxine-binding globulin (TBG) was found in 6 members of a family who displayed no clinical manifestations of thyroid disease. This protein-binding defect appears to be transmitted as a mendelian autosomal dominant. The decreased binding by TBG was associated with a decreased concentration of PBI (1.9–3.3 μg/100 ml). A compensatory increase in the fractional rate of disappearance of thyroxine from the plasma resulted in a normal rate of daily hormonal turnover in the propositus. Although predictable elevations in TBG-binding capacity are found in normal pregnancy, extrapolations of the present data suggest that disparate thyroxine-binding capacities between mother and fetus do not affect gestation. This trait is thus an isolated, benign defect of a serum protein.