Inherited decrease of the binding capacity of thyroxine-binding globulin (TBG).

Abstract

ABSTRACT A family with a decrease in the binding capacity of thyroxine binding globulin (TBG) is described. The gene was probably transmitted by a female who married twice. Five subjects were considered TBG deficient, with TBG values ranging from 8.4 to 16.8 μg/100 ml. Of these subjects 2 were males and 3 females; the males had the lowest binding capacities. In addition, 1 male and 3 females had TBG values within the low normal range and were considered as possibly affected. The mode of inheritance could not be exactly defined but there were indications that it might be an autosomal dominant. The correlation of TBG to the protein-bound iodine in the serum (PBI), to the triiodothyronine uptake by Sephadex (T3-U), to the ratio between them (T3-U/PBI), and to the proportionate free thyroxine (PFT4) was strongly positive or negative. A gradual change in these variables from the affected to the unaffected subjects was observed. These correlations indicated that in normal subjects TBG is the most important factor governing the PBI and free thyroxine levels. In addition, a strong inverse and statistically significant correlation was observed between the binding capacity of TBG and that of the pre-albumin (TPBA). The difference between affected and unaffected subjects with regard to TPBA was also statistically significant.