Minor component of the myelin sheath. May be involved in completion and/or maintenance of the myelin sheath and in cell-cell communication. Mediates homophilic cell-cell adhesion. Homodimer. Found exclusively in the CNS, where it is localized on the surface of myelin and oligodendrocyte cytoplasmic membranes. Reduced expression levels are observed in jimpy and quacking dysmyelinating mutant mice. Belongs to the immunoglobulin superfamily. BTN/MOG family. Do not confuse myelin-oligodendrocyte glycoprotein (MOG) with oligodendrocyte-myelin glycoprotein (OMG).