Familial thyroxine-binding globulin deficiency.

Genetically determined thyroxine-binding globulin deficiency is described in two families in the United Kingdom. All subjects in both pedigrees were euthyroid. Transmission was by sex-linkage; males showed low serum protein bound iodine and high thyroxine (T4) resin uptake due to complete absence of serum thryroxine-binding globulin; females were less severely affected. The distinctive biochemical results disclosed the diagnosis and emphasize that serum protein bound iodine levels should be interpreted carefully and tests, such as triiodothyroinine (T3) or T4 resin uptake, used to prevent erroneous diagnoses of hypothyroidism.