A classic example of a “primary” astrocytic disease is Alexander disease (AxD), a human neurological disorder unequivocally caused by a dysfunction of astrocytes due to mutations in the gene encoding glial fibrillary acidic protein (GFAP) (Brenner, Goldman, Quinlan, & Messing, 2009; Messing, Brenner, Feany, Nedergaard, & Goldman, 2012). Here, GFAP is linked to Alexander disease.