AQP4 and autoimmune disease: Anti-aquaporin-4 antibody (anti-AQP4-Ab)-associated neuromyelitis optica spectrum disorder (NMOSD) is a rare autoimmune disease affecting the central nervous system (CNS).1 Optic nerves and spinal cord are the most frequently involved structures, due to the extensive expression of AQP4;1 however, NMOSD-associated lesions might also develop, in some cases, in circumventricular structures and within brain white matter.2