Loss of AQP4 from perivascular membranes occurs in epilepsy (Eid et al. 2005; Alvestad et al. 2013), stroke (Frydenlund et al. 2006), brain injury (Ren et al. 2013), and Alzheimer’s disease (Yang et al. 2011), but the mechanisms are poorly understood (Wolburg et al. 2011). This evidence concerns the gene AQP4 and Alzheimer disease.