Contactin 4 is a 1,026 amino acid protein encoded by the human gene CNTN4. Contactin 4 belongs to the immunoglobulin superfamily and is a member of the Contactin family. Contactin 4 contains four fibronectin type-3 domains, six Ig-like C2-type domains, and has three isoforms (1,2,3). Defects in the CNTN4 gene are a cause of 3p deletion syndrome (3PDS). 3PDS is a rare contiguous gene disorder involving the loss of the telomeric portion of the short arm of chromosome 3 and is characterized by