Alexander disease

**Definition:** Alexander's disease is a neurodegenerative disorder encompassing different clinical forms: the infantile form (birth to 2 years), the most common, is characterised by its early onset and severe evolution with progressive megalencephaly (sometimes hydrocephaly), retarded psychomotor development or mental deterioration, pyramidal signs, ataxia and convulsive seizures. The juvenile forms start in school-aged children and associate spastic paraplegia and progressive bulbar signs. Adult forms are heterogeneous and difficult to diagnose.