Contactin-5 (CNTN5), also known as NB-2, is a neural adhesion molecule in the contactin family of the immunoglobulin superfamily. The contactin family comprises six members (CNTN1/F3, CNTN2/TAG-1, CNTN3/BIG-1, CNTN4/BIG-2, CNTN5/NB-2 and CNTN6/NB-3) that are characterized by the presence of six Ig-like domains, four fibronectin type III-like repeats, and a glycosylphosphatidylinositol (GPI)-anchoring domain (1, 2). The human Contactin-5 cDNA exists in two splice forms which contain an 18 amino acid (aa) signal sequence and a 28 aa C-terminal propeptide. The long isoform is a 1082 aa protein that shares 91% aa sequence identity with rat and mouse Contactin-5. The short isoform lacks the first 74 aa at the N-terminus of the long isoform. Human Contactin-5 shares 43%, 41%, 52%, 52%, and 48% aa identity with Contactins-1,-2,-3,-4, and -6, respectively (3). Contactin family proteins exist as membrane-bound proteins, but can also be released as soluble proteins by GPI-specific phospholipase D. The gene encoding Contactin-5 is localized to a chromosomal region associated with schizophrenia and the neuronal disorder Jacobsen syndrome (4). The highest expression of human Contactin-5 is seen in occipital lobe and amygdala, followed by cerebral cortex, frontal lobe, thalamus, and temporal lobe (4). In rat, Contactin-5 is highly expressed specifically in structures of the central auditory pathway (5). Also in rat, Contactin-5 has been shown to promote neurite outgrowth of cerebral cortical neurons in vitro (5). Deficient Contactin-5 expression in mice results in impaired neuronal activity of the central auditory system (6).