For a long time, LDs were thought to be caused by mutations in oligodendrocyte specific genes, but the identification of some LDs caused by mutations in astrocyte unique genes, such as the glial fibrillary acidic (GFAP) gene in Alexander disease (AxD) and MLC1 in Megalencephalic leukoencephalopathy with subcortical cyst disease (MLC), completely changed this view. This evidence concerns the gene GFAP and Alexander disease.