Transthyretin is a protein produced primarily in the liver and the choroid plexus of the brain. It plays a crucial role in transporting vitamin A and thyroxine, a hormone produced by the thyroid gland. Transthyretin is a tetramer, meaning it is made up of four identical subunits, which helps it maintain stability and function in the bloodstream. In certain conditions, such as transthyretin amyloidosis, the protein can misfold and form amyloid fibrils, leading to tissue damage and various health issues. This misfolding can result in a range of symptoms, including heart problems and neuropathy, making early diagnosis and treatment essential for affected individuals.