Journal of Clinical Endocrinology & Metabolism, Vol 63, 1140-1144, Copyright © 1986 by Endocrine Society

ARTICLES

Inherited heat-stable variant thyroxine-binding globulin (TBG-Chicago)

J Takamatsu and S Refetoff

The five known types of inherited variant T4-binding globulin (TBG) have in common increased sensitivity to heat denaturation compared to the common type TBG (TBG-C). In the course of studies to screen for and characterize variant TBGs in population groups, we detected a unique TBG with marked resistance to heat denaturation. The propositus was a 22-year-old black man without personal or family history of thyroid disease. His native TBG (nTBG) in serum had a t1/2 of denaturation at 56 C of 90 min compared to a mean value of 6.8 +/- 1.1 (+/- SD) min for TBG-C. This variant TBG, termed TBG-Chicago, was also resistant to acid denaturation, but was indistinguishable from TBG-C in terms of immunoreactivity, microheterogeneity on isoelectric focusing, and affinity for T4. It had a single T4-binding site and a normal concentration in serum associated with iodothyronine levels within the normal range. The mode of inheritance of TBG-Chicago appears to be X- chromosome linked. The mother of the propositus was heterozygous; her serum contained approximately 40% TBG-Chicago and 60% of another variant TBG common in blacks, TBG-S. The father had TBG-C, a trait that was not transmitted to his son. The exact nature of this variant TBG is not known. It most likely represents a mutation in the polypeptide chain of the molecule with formation of stronger intramolecular bonds.

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				O. E. Janssen, B. Chen, C. Büttner, S. Refetoff, and P. C. Scriba Molecular and Structural Characterization of the Heat-resistant Thyroxine-binding Globulin-Chicago J. Biol. Chem., November 24, 1995; 270(47): 28234 - 28238. [Abstract] [Full Text] [PDF]