Multiple sclerosis (MS), aquaporin-4 antibody positive neuromyelitis optica spectrum disorder (AQP4-Ab + ve NMOSD), and myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) are three discrete autoimmune diseases of the central nervous system (CNS) that cause demyelination. The gene discussed is AQP4; the disease is multiple sclerosis.