Review of Alexander disease: beyond the classical concept of leukodystrophy.

Alexander disease is classified as one of the leukodystrophies, which are degenerative diseases primarily affecting the cerebral white matter. Formal diagnosis is achieved by showing diffuse accumulation of Rosenthal fibers in the brain by biopsy or autopsy. Showing a heterozygous mutation in the glial fibrillary acidic protein (GFAP) gene is currently sufficient for diagnosis. The mechanisms of Rosenthal fiber formation remain unclear. However, both the quality and quantity of GFAP are important. GFAP-epsilon (rodent homologous GFAP-delta), one of the alternatively spliced GFAP isoforms, may also play a modulating role in aggregate formation. The current ease of diagnosis has accelerated the accumulation of a wide variety of patients with Alexander disease along with the widespread use of MRI. In contrast to the classical infantile type, patients with juvenile and adult types mainly complain of bulbar symptoms and usually show progressive atrophy of the lower brainstem and cervical spinal cord with mild or minimal leukodystrophic changes. Among the many MRI findings of Alexander disease, periventricular linear lesions with various names depending on the thickness and shape seem to represent the unique pathophysiology, because the subventricular zone of the adult human brain includes special astrocytes that behave as multipotent progenitor cells and specifically produce GFAP-epsilon. Except for a few mutations, no clear phenotype-genotype correlation has been established for Alexander disease, although male preponderance in the infantile type suggests that phenotypes may be partly affected by gender.