GFAP is a cell-specific marker which belongs to the intermediate filament family. It can distinguish astrocytes from other glial cells during development. GFAP is expressed in cells lacking fibronectin. It is a type III intermediate filaments protein which contains three domains: the head, rod and tail domains. GFAP functions in many important entral nervous system (CNS) processes, including cell communication and the functioning of the blood brain barrier. Improper GFAP regulation can cause multiple disorders. Defects in GFAP is related to Alexander disease which is a rare disorder of the central nervous system. It is a progressive leukoencephalopathy whose hallmark is the widespread accumulation of Rosenthal fibers which are cytoplasmic inclusions in astrocytes.