In a subgroup of AQP4 antibody (AQP4-IgG) seronegative NMOSD patients as well as in patients with recurrent optic neuritis and a few patients with multiple sclerosis (MS) an antibody against myelin oligodendrocyte glycoprotein (MOG-IgG) can be detected (23–33). Here, AQP4 is linked to optic neuritis.