Familial Elevation of Serum Thyroxine-Binding Capacity

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Abstract
A family is described in which members in 3 generations showed serum protein-bound iodine levels well above the normal range without evidence of hypermetabolism. The saturation capacity of the serum thyroxine-binding globulin fraction (TBG) was grossly elevated in the affected cases ro valres usually observed only in pregnancy and after estrogen therapy. The 3 children investigated, one of whom shewed elevation of the TBG, had saturation values of the pre-albumin thyroxine-binding proteins (TBPA) well below the normal range accepted for normal adults, and this also wao found in a small series of children without thyroid abnormality. The incidence of the elevated-TBG trait in the pedigree is consonant with transmission by a dominant gene. A number of methods of evaluating serum thyroxine binding that are carried out under physiologic conditions of pH and thyroxine concentration have been compared with electrophoretically determined TBG and TBPA levels, and the findings are discussed in relation to the physiologic role of the 2 binding proteins.