Neuromyelitis optica spectrum disorder (NMOSD) is a type of astrocytopathy in which aquaporine-4 (AQP4)-IgG antibodies bind to AQP4 water channels on the end feet of astrocytes, leading to immune-mediated inflammation and secondary demyelination that can occur in varying degrees (15, 16). The gene discussed is AQP4; the disease is neuromyelitis optica.