Neural Cell Adhesion Molecule (NCAM, also the cluster of differentiation CD56) is a homophilic binding glycoprotein expressed on the surface of neurons, glia, skeletal muscle and natural killer cells. NCAM has been implicated as having a role in cell–cell adhesion, neurite outgrowth, synaptic plasticity, and learning and memory. NCAM is a glycoprotein of Immunoglobulin (Ig) superfamily. The three main isoforms of NCAM vary only in their cytoplasmic domain: NCAM-120kDa (GPI anchored), NCAM-140kDa (short cytoplasmic domain) and NCAM-180kDa (long cytoplasmic domain).