Contactin-4, is an axonal cell adhesion molecule (AxCAM) that belongs to the contactin family, a subfamily of the Ig superfamily (1, 2). 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 (1-4). Contactins are membrane-anchored proteins that can be released as soluble proteins by GPI-specific phospholipase D and are able to promote neurite outgrowth in their soluble form (2). Potential 1026, 705-498aa isoforms of mouse CNTN4 have been described (1, 5). Only the longest isoform includes the C-terminal GPI anchoring sequence. It shares 97% aa identity with rat and 95aa identity with human, equine and bovine CNTN4 in its mature 981aa form. It also shares 42-64% aa identity with other CNTN family members, showing highest identity with CNTN3. CNTN4 is expressed throughout the brain, but minor amounts are also detected in small intestine, thyroid, uterus and testis (2, 4). Family members display overlapping but distinct expression patterns in rat brain and are suggested to influence the formation and maintenance of specific neuronal networks (2). In the olfactory bulb, CNTN4 is expressed in specific sensory neurons in a mosaic pattern that is closely correlated with odorant receptor choice, and is thought important for odor mapping (6, 7). In humans, disruption of CNTN4 has been implicated in the 3p deletion syndrome characterized by developmental and growth delay, and in autism spectrum disorder (8-10).