AQP4 and neuromyelitis optica: Myelin oligodendrocyte glycoprotein (MOG) antibody immunoglobulin G (IgG)-associated disease (MOGAD) has clinical and pathophysiological features-like but distinct from those of aquaporin-4 antibody (AQP4-IgG)-positive neuromyelitis optica spectrum disorders (AQP4-NMOSD).