Alexander disease is one of a group of neurological conditions known as the leukodystrophies, disorders that are the result of abnormalities in myelin, the “white matter” that protects nerve fibers in the brain. Alexander disease is a progressive and usually fatal disease. The destruction of white matter is accompanied by the formation of Rosenthal fibers, which are abnormal clumps of protein that accumulate in non-neuronal cells of the brain called astrocytes. Rosenthal fibers are sometimes found in other disorders, but not in the same amount or area of the brain that are featured in Alexander disease. The infantile form is the most common type of Alexander disease. It has an onset during the first two years of life. Usually there are both mental and physical developmental delays, followed by the loss of developmental milestones, an abnormal increase in head size, and seizures. The juvenile form of Alexander disease is less common and has an onset between the ages of two and thirteen. These children may have excessive vomiting, difficulty swallowing and speaking, poor coordination, and loss of motor control. Adult-onset forms of Alexander disease are rare, but have been reported. The symptoms sometimes mimic those of Parkinson’s disease or multiple sclerosis. The disease occurs in both males and females, and there are no ethnic, racial, geographic, or cultural/economic differences in its distribution.