AQP4 and neuromyelitis optica: This suggests that the first step in pathogenesis, in NMO and other in autoantibody-mediated CNS diseases, is BBB disruption: in the case of NMO due either to antibodies directed against AQP4 within the BBB43 or to induction of IL-6 production by AQP4-positive astrocytes.44 This disruption may allow leakage of AQP4 antibodies into the cerebrospinal fluid (CSF).45 We have reviewed the implications of BBB dysregulation in psychosis elsewhere.46