AQP4 and demyelinating disease: Neuromyelitis optica spectrum disorder (NMOSD), formerly referred to as neuromyelitis optica (NMO) or Devic’s disease, is a demyelinating disorder thought to be caused by immunoglobulin G (IgG) antibodies targeting water channel protein aquaporin 4 (AQP4) located in astrocytic foot processes contributing to the formation of blood-brain barrier (BBB) [1].