© 2014 Elsevier Inc. All rights reserved. Alexander's disease can occur at any age. Children typically present with delayed development, seizures, and macrocephaly, whereas older patients generally display bulbar symptoms. Myelin defects can be severe in younger patients, but subtle or absent in older patients. Nearly all cases are due to mutations in the gene-encoding glial fibrillary acidic protein (GFAP), an intermediate filament (structural) protein found almost exclusively in astrocytes. Although this marks astrocytes as the primary disease site, the clinical findings are attributed to oligodendrocyte and neuron dysfunction. How GFAP mutations produce these dysfunctions is not known, nor is a cure presently available.