• 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 fibres in the brain.

• Its prevalence is unknown but it is extremely rare. It is thought that between about 300 and 500 cases have been reported since the disorder was first described in 1949.

• The majority of sufferers have a mutation in the gene that makes glial fibrillary acidic protein; most of the mutations occur without any known cause and are not inherited from parents.

• There is no cure for the disease and most children with the infantile form are not expected to survive past the age of six. There is no standard treatment.

• The disease results in mental and physical developmental delays, followed by the loss of developmental milestones, an abnormal increase in head size and seizures.

• It occurs in both males and females and there are no ethnic, racial, geographic, cultural or economic differences in its distribution.

Information from the National Institute of Neurological Disorders and the National Library of Medicine in the US.