AQP4 and neuromyelitis optica: MOG-IgG has been shown in multiple studies from independent researchers to be a specific serum biomarker of a subset of central nervous system (CNS) inflammatory demyelinating diseases (IDD), clinically distinct from MS and aquaporin-4 (AQP4) antibody (Ab) seropositive neuromyelitis optica spectrum disorder (NMOSD) [9, 29, 34, 45, 51, 53, 62, 63].