AQP4 and multiple sclerosis: The NMOSD diagnostic criteria comprise two different groups regardless of AQP4-IgG positivity.4According to Sato et al., 21.1% of AQP4-IgG-negative NMOSD patients are positive for a different antibody, myelin oligodendrocyte glycoprotein-IgG (MOG-IgG).5Interestingly, although this protein was initially thought to be involved in the pathophysiogenesis of multiple sclerosis (MS), its role in a new entity known as myelin oligodendrocyte glycoprotein associated-disease (MOGAD) is now recognized.6