AQP4 and neuromyelitis optica: Excitingly, the autoantibodies that target the aquaporin‐4 (AQP4) water channel protein were discovered and evidenced to have pathogenic potential for neuromyelitis optica (NMO) in 2004,12, 13 providing a better way to identify and diagnose NMOSD based on the presence of AQP4 immunoglobulin G (AQP4‐IgG).2, 14