<h4>Background</h4>Neuromyelitis optica spectrum disorders (NMOSD) are an immune-mediated inflammatory disease of the central nervous system (CNS) primarily characterized by anti-aquaporin-4 immunoglobulin G (AQP4-IgG)-mediated astrocyte injury, neuroinflammation, and demyelination. The gene discussed is AQP4; the disease is neuromyelitis optica.