Neuromyelitis optica spectrum disorder (NMOSD) is a rare, autoimmune disease of the central nervous system (CNS) in which approximately 75–90% of patients harbour pathogenic immunoglobulin (Ig) G autoantibodies against the aquaporin-4 water channel (AQP4-IgG).1 This evidence concerns the gene AQP4 and neuromyelitis optica.