AQP4 and neuromyelitis optica: In contrast to MS, its related disorders—AQP4 + neuromyelitis optica (NMO) and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD)—meet (or nearly meet) autoimmune criteria, with identification of specific antigens that elicit both antibody and T-cell responses, as well as therapeutic responses to antigen removal or neutralization of effector pathways.21, –23 While animal models exist for these disorders, key questions remain.