Neuromyelitis optica (NMO), characterized by recurrent episodes of longitudinally extensive transverse myelitis and/or optica neuritis, is another autoimmune inflammatory demyelinating disorder of CNS, which is distinct from MS in both mechanism of action and clinic treatment after discovery of the serum aquaporin 4 antibody (AQP4-Ab). The gene discussed is AQP4; the disease is myeloid sarcoma.