Antibodies to AQP4 are also frequently detected in so called "High-risk NMO" (HR-NMO) patients not fulfilling all diagnostic criteria for NMO, who present with NMO-associated symptoms like recurrent optic neuritis (ON) or longitudinally extensive transverse myelitis (LETM) extending more than three vertebral segments [10]. This evidence concerns the gene AQP4 and neuromyelitis optica.