MOG-IgG antibody is a biomarker of MOG-associated encephalomyelitis (MOG-EM), a relatively rare demyelinating disease characterized by different clinical manifestations, including recurrent and bilateral optic neuritis, transverse myelitis, brain stem encephalitis, and acute disseminated encephalomyelitis (ADEM) [25,52,53]. This evidence concerns the gene MOG and optic neuritis.