Whether the presence of an autoantibody against AQP4 is the cause of the disease or a collateral consequence of some secondary pathological mechanisms still lacks an unanimous answer, but studies performed where immunoglobulins taken from AQP4 antibody positive NMO patients were administered to rats with EAE showed NMO pathology seen in the clinics [48,49], suggesting that the presence of AQP4 autoantibody in patients already suffering from neuroimmune disease worsens the condition and leads to the NMO pathology observed. This evidence concerns the gene AQP4 and neuromyelitis optica.