Glial fibrillary acidic protein, or GFAP, is a class III intermediate filament. During development of the central nervous system, GFAP distinguishes astrocytes from other glial cells. It is involved in various cellular functions, such as cell structure and movement, cell communication and the functioning of the blood­brain barrier. It also plays a role in mitosis by adjusting the filament network present in the cell. Defects in GFAP are a cause of Alexander disease, a rare disorder of the central nervous system affecting mostly males. It is a progressive leukoencephalopathy resulting in mental and physical retardation, dementia, seizures and early death.