TTR (Transthyretin) is a prealbumin carrier protein that transports thyroid hormones in the plasma and cerebrospinal fluid as well as retinol (vitamin A) in the plasma. There are numerous mutations in TTR related to amyloid deposition, primarily impacting peripheral nerves and the heart. These mutations lead to a number of diseases, including amyloidotic polyneuropathy, amyloidotic vitreous opacities, euthyroid hyperthyroxinaemia, cardiomyopathy, oculoleptomeningeal amyloidosis, meningocerebrovascular amyloidosis, and carpal tunnel syndrome. In immunohistochemistry of normal tissue, TTR has secretory positivity in plasma and is also found in the liver, the brain, in pancreatic islets and in renal tubules. References: The UniProt Consortium. Nucleic Acids Res. 47: D506-515 (2019); Nucleic Acids Res. 2016 Jan 4;44(D1):D733-45, PMID:26553804; Circulation. 2012 Sep 4;126(10):1286-300, PMID: 22949539; Nat Rev Neurol 15, 387–404 (2019), DOI:10.1038/s41582-019-0210-4