Transthyretin (TTR), a plasma and cerebrospinal fluid protein secreted by the 
liver and choroid plexus, is mainly known as the physiological carrier of 
thyroxine (T(4)) and retinol. Under pathological conditions, various TTR 
mutations are related to familial amyloid polyneuropathy (FAP), a 
neurodegenerative disorder characterized by deposition of TTR amyloid fibrils, 
particularly in the peripheral nervous system (PNS), leading to axonal loss and 
neuronal death. Recently, a number of TTR functions in neurobiology have been 
described; these may explain the preferential TTR deposition, when mutated, in 
the PNS of FAP patients. In this respect, and with a particular relevance in the 
PNS, TTR has been shown to have the ability to enhance neurite outgrowth in 
vitro and nerve regeneration following injury, in vivo. In the following pages, 
this novel TTR function, as well as its importance in nerve biology and repair 
will be discussed.