NMOSD (also known as Devic’s disease) is a relapsing disease with the typical triad of optic neuritis, myelitis, and positive NMO-IgG, an autoantibody to the protein channel aquaporin-4 (AQP4), which is expressed on foot processes of astrocytes (Fig. 6). The gene discussed is AQP4; the disease is neuromyelitis optica.