Extensive investigations, including cerebrospinal fluid (CSF) analysis and testing for myelin oligodendrocyte glycoprotein (MOG-IgG) and aquaporin-4 (AQP4-IgG) antibodies, were negative, suggesting a seronegative monophasic demyelinating event such as acute disseminated encephalomyelitis (ADEM) spectrum. The gene discussed is MOG; the disease is acute disseminated encephalomyelitis.