The present disclosure provides for the diagnosis and prediction of neuromyelitis optica (NMO) in subject. It also provides for treatment of multiple sclerosis (MS) in a subject. Thus, in accordance with the present disclosure, there is provided a method for treating a subject having neuromyelitis optica (NMO) comprising administering to said subject an inhibitor of B-cell activating factor (BAFF) and/or an inhibitor or proliferating inducing ligand (APRIL).