Whereas clear positive MOG-IgG titres are strongly associated with the clinical features proposed for MOGAD (optic neuritis, myelitis, ADEM, cerebral monofocal or polyfocal deficits, brainstem and cerebellar deficits and cortical encephalitis with seizures) and at the same time distinguish them from clinical features characteristic of AQP4-IgG-seropositive neuromyelitis optica spectrum disorder (NMOSD) or multiple sclerosis (MS). The gene discussed is AQP4; the disease is optic neuritis.