A Possible New Syndrome of Familial Euthyroid Dysproteinemia Associated with Elevated Thyroxine and Triiodothyronine

Increased thyroxine (T₄) binding to thyroid binding prealbumin (TBPA) or albumin causes a biochemical picture suggestive of thyrotoxicosis with increased total T₄(TT₄). Previously described familial syndromes are characterized by increased binding of T₄ to thyroid binding globulin (TBG), TBPA, or albumin. Increased T₃ binding to TBG has been noted, but we are not aware of any kindreds reported with increased T₃ binding to TBPA or albumin. We wish to report a family in which there is increased binding of T₃ to TBG, TBPA and albumin. All family members were clinically euthyroid and tested negative for T₃ antibodies. This family appears to demonstrate two abnormalities: First, elevated TBG, and second, normal levels of TBPA and albumin with increased binding of T₃ and T₄ to these proteins. We believe this may represent a new syndrome of familial dysproteinemia in which multiple proteins show enhanced binding of T₃ and T₄. This could reflect increased binding sites, increased binding affinity, or a combination of both.