Alexander disease, a leukodystrophy, is a progressive and usually fatal neurological disorder in which the destruction of white matter in the brain is accompanied by the formation of abnormal deposits known as Rosenthal fibers. Rosenthal fibers are aggregations of protein that occur in astrocytes, which are cells that support the brain. These protein collections are found occasionally in other disorders, but not with the abundance or particular distribution in the brain that occurs in Alexander disease.

The most common form of Alexander disease is the infantile form, which usually becomes apparent during the first two years of life. Typically, there are both mental and physical developmental delays, followed by loss of milestones, an abnormal increase in head size, and often seizures. The juvenile form of Alexander disease is less common and generally has onset between the ages of four and 15. These children may have excessive vomiting, difficulty swallowing and speaking, poor coordination, and loss of motor control. Survival is quite variable, with rare juvenile cases surviving several decades. Adult-onset forms of Alexander disease exist, and are sometimes confused clinically with multiple sclerosis or Parkinson’s disease. The disease occurs in both sexes and there are no ethnic, racial, geographic, or cultural/economic differences in its distribution.