Mutations associated with an increased concentration of TTR do not cause euthyroid hyperthyroxinemia, as an observed augmentation in the protein level is not high enough (although in the course of some malignancies e.g. hepatocellular carcinoma, the TTR concentration may increase significantly and bring about the picture of euthyroid hyperthyroxinemia) [39]. This evidence concerns the gene TTR and hyperthyroxinemia.