AQP4 and neuromyelitis optica: Some autoantibodies in this group of disorders are considered pathogenic such as aquaporin-4 (AQP4) in neuromyelitis optica spectrum disorder (NMOSD), whereas other antibodies are not directly pathogenic but are rather markers of cytotoxic T cell mediated autoimmunity [i.e., collapsin receptor mediator protein-5 (CRMP5)].