AQP4 and neuromyelitis optica: Also, when AQP4 is dysfunctional and/or lost as in the clinical diseases neuromyelitis optica [81,82] and neuromyelitis optica spectrum disorders [83,84] as a result of autoantibodies against the AQP4 water channel as well as the genetic knockout rodent models, which are associated with EPVS [11,85], there is dysfunction of the brain.