Hyperthyroxinemia and Hypercortisolemia due to Familial Dysalbuminemia

A 23-year-old man and his grandmother with hyperthyroxinemia and hypercortisolemia were heterozygous for anALBmutation (p. Arg218Pro), known to cause familial dysalbuminemic hyperthyroxinemia (FDH). However, serum-free cortisol levels in these individuals were normal and total cortisol concentrations fell markedly after depletion of albumin from their serum. We conclude that binding of steroid as well as iodothyronines to mutant albumin causes raised circulating cortisol as well as thyroid hormones in euthyroid euadrenal individuals with R218P FDH, with potential for misdiagnosis, unnecessary investigation, and inappropriate treatment.