AQP4 and neuromyelitis optica: Neuromyelitis optica spectrum disorders (NMOSD) are inflammatory disorders of the CNS characterized by severe, immune-mediated demyelination and axonal damage predominantly targeting optic nerves and spinal cord, in which the high specificity of aquaporin-4 (AQP4)–immunoglobulin G (IgG) has allowed to recognize other sites of CNS involvement not restricted to the optic nerves and spinal cord as well as diencephalon, brainstem and the brain [37].