AQP4 and neuromyelitis optica: Compellingly, NMO is now more appropriately referred to as neuromyelitis optica spectrum disorder (NMOSD), reflecting that the condition can be triggered in multiple ways, for example, by antibodies targeting aquaporin-4 expressed on astrocytes or, alternatively, by antibodies directed against the oligodendrocyte-specific myelin oligodendrocyte glycoprotein (5, 6).