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 developmental delay, growth retardation, and dysmorphic features. Contactin 4 is primarily expressed in brain tissue. Highest expression has been found to be in the cerebellum, with lowest levels found in corpus callosum, caudate nucleus, amygdala and spinal cord. Some expression is also found in testis, pancreas, thyroid, uterus, small intestine and kidney. Contactin 4 is not believed to be expressed in skeletal muscle. Isoform 2 is weakly expressed in cerebral cortex.