AQP4 and neuromyelitis optica: Anti-aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorder (NMOSD), anti-myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), and multiple sclerosis (MS) are distinct autoimmune-related relapsing neurological diseases of the central nervous system (CNS)1–3.