Molecular basis of inherited thyroxine-binding globulin defects.

Thyroxine-binding globulin (TBG) is a liver glycoprotein that transports thyroid hormones in serum. Inherited TBG defects appear as partial or complete deficiency and TBG excess. Sequencing of the TBG gene located on the X-chromosome has revealed nucleotide substitutions in partial TBG deficiency, and substitutions or deletions in complete deficiency variants. Whereas the deduced changes of the primary structure of the protein have been sufficient to explain the observed alterations of properties in some of the TBG variants, this has not been the case in other inherited TBG defects studied at the gene level. Further analysis of these and other variants may provide helpful information on glycoprotein synthesis and processing and on protein-hormone interaction.