Since its ?rst description in 1942 in both serum and cerebrospinal ?uid, transthyretin (TTR) has had an eventful history, including changes in name from ¿prealbumin¿ to ¿thyroxine-binding prealbumin¿ to ¿transthyretin¿ as knowledge increased about its functions. TTR is synthesised in a wide range of tissues in humans and other eutherian mammals: the liver, choroid plexus (blood- cerebrospinal ?uid barrier), retinal pigment epithelium of the eye, pancreas, intestine and meninges. However, its sites of synthesis are more restricted in other vertebrates. This implies that the number of tissues synthesising TTR during vertebrate evolution has increased, and raises questions about the selection pressures governing TTR synthesis. TTR is