Clinical and neuroradiological characteristics of 23 patients with neuromyelitis optica or relapsing myelitis who are seropositive for AQP4 autoantibodies by cell-based IIFA, divided into those who are seropositive and seronegative for NMO-IgG by tissue-based IIFA. The gene discussed is AQP4; the disease is neuromyelitis optica.