GFAP is a 50 kDa intra-cytoplasmic filamentous protein of the cytoskeleton in astrocytes, and it has demonstrated to be the most specific marker for cells of astrocytic origin. FUNCTION: GFAP, a class-III intermediate filament, is a cell-specific marker that, during the development of the central nervous system, distinguishes astrocytes from other glial cells. GFAP immunoreactivity has been shown in immature oligodendrocytes , epiglottic cartilage, pituicytes, papillary meningiomas, myoepithelial cells of the breast and in non-CNS: Schwann cells, salivary gland neoplasms, enteric glia cells, and metastasizing renal carcinomas. SUBCELLULAR LOCATION: Cytoplasm. Note: Associated with intermediate filaments. ALTERNATIVE PRODUCTS: 3 named isoforms produced by alternative splicing. Isoforms differ in the C-terminal region which is encoded by alternative exons. DISEASE: Defects in GFAP are a cause of Alexander disease. Alexander disease 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. The most common form affects infants and young children, and is characterized by progressive failure of central myelination, usually leading to death within the first decade. Patients with juvenile or adult forms typically experience ataxia, bulbar signs and spasticity, and a more slowly progressive course.