The collapsin response mediator protein (CRMP) family of proteins (also referred to as ULIP6) are a group of neurologic proteins that have been found to play key roles in growth cone guidance during neural development. CRMP5 has relatively low sequence homology with the other four members of the CRMP family. CRMP5 is expressed in the developing nervous system in an expression pattern that resembles CRMP2 and has a peak expression during the first postnatal week. Elevated levels of autoantibody to CRMP5 have been shown to be linked paraneoplastic autoimmune optic neuritis and other paraneoplastic neoplasms. Auto-immunity against CRMP5 expression (predominantly the N-terminal epitopes) is also being investigated as an oncological marker in the respiratory system and in the thymus.