The proposed diagnostic criteria for MOG-EM are based on a combination of [1] monophasic or relapsing acute optic neuritis, myelitis, brainstem encephalitis, or encephalitis, or any combination thereof; [2] MRI or electrophysiological (visual evoked potentials in patients with isolated optic neuritis) findings compatible with CNS demyelination; and [3] seropositivity for MOG-IgG as detected by means of a cell-based assay employing full-length human MOG as target antigen [28, 29]. This evidence concerns the gene MOG and encephalitis.