AQP4 and neuromyelitis optica: Neuromyelitis optica spectrum disorders are also inflammatory demyelinating diseases affecting CNS, characterized clinically by attacks of myelitis and optic neuritis and biologically by the presence of highly specific and pathogenic autoantibodies directed against the extracellular domain of the water channel protein aquaporin-4 expressed in astrocytes (NMO-IgG) (154).