AQP4 and neuromyelitis optica: Recent evidences such as the discovery of serum anti-aquaporin-4 (AQP4) antibody in NMO patients [7] (now recognised as a specific biomarker for NMO), differences in pathology [8], neuroimaging [9], cytokine profiles [10,11] and responses to some immunotherapies between MS and NMO [12], supports the hypothesis that NMO is distinct from MS.