The majority of MOG-IgG-seropositive cases have ON, encephalitis with brain demyelinating lesions, and/or myelitis; thus, we propose the new term MOG-IgG-associated ON, encephalitis, and myelitis (MONEM) to encompass this group of patients with CNS demyelinating syndromes associated with MOG-IgG (Figure 1). The gene discussed is MOG; the disease is encephalitis.