The discovery of the NMO-immunoglobulin G (NMO-IgG) antibody in the serum of patients with this condition and subsequent identification of the target antigen anti-aquaporin-4 (AQP4) [3] suggested that the pathogenesis of NMO differs from that of multiple sclerosis (MS). The gene discussed is AQP4; the disease is neuromyelitis optica.