GFAP (Glial fibrillary acidic protein) is a member of the class III intermediate filament protein family. GFAP is heavily and specifically expressed in astrocytes and certain astroglia of the central nervous system, in satellite cells of peripheral ganglia, and in non-myelinating Schwann cells of peripheral nerves. In addition, neural stem cells strongly express GFAP. Antibodies to GFAP are very useful as markers of astrocytic cells. In addition, many types of brain tumor, presumably derived from astrocytic cells, heavily express GFAP. GFAP is also found in the lens epithelium, Kupffer cells of the liver, in some cells in salivary tumors and has been reported in erythrocytes. GFAP is used as a marker to distinguish astrocytes from other glial cells during development. Mutations in this gene cause Alexander disease, a rare disorder of astrocytes in the central nervous system. Alternative splicing of the GFAP gene results in multiple transcript variants encoding distinct isoforms.