Inflammatory demyelinating diseases (IDDs) of the central nervous system (CNS) are immune-mediated disorders that lead to the destruction of myelin, either primarily [multiple sclerosis (MS) and myelin oligodendrocyte glycoprotein-antibody-associated disease (MOGAD)] or secondarily [neuromyelitis optica spectrum disorder (NMOSD)]. The gene discussed is MOG; the disease is neuromyelitis optica.