TTR (Transthyretin) is a tetrameric protein primarily produced by the liver and choroid plexus. It transports thyroid hormones and retinol-binding protein in plasma and cerebrospinal fluid, contributing to the regulation of metabolism and visual function. TTR maintains the homeostasis of thyroid hormones and retinol-binding protein by binding to them, influencing multiple biological responses and signaling pathways. The expression of the TTR gene is tissue-specific, and its mutations are associated with familial amyloidotic polyneuropathy (ATTR), a hereditary disease that damages peripheral nerves and the heart, severely affecting patients' quality of life and lifespan.