DSCAM (Down syndrome cell adhesion molecule) is a 230 kD axonal guidance molecule that is a member of the Ig superfamily. It is synthesized as a mature, 2005 amino acid (aa) type I transmembrane glycoprotein. There is a large, 1578 aa extracellular domain (ECD) and a 389 aa cytoplasmic region. The ECD shows ten C2-type Ig-like domains and six fibronectin type III repeats. One soluble splice form is known which contains all the ECD modules and ends after aa # 1571 of the precursor. This form has a unique C-terminal ten amino acids. DSCAM is found on axonal and dendritic processes. It also forms homophilic complexes among cells.