AQP4 and neuromyelitis optica: MOG antibodies (MOG-Ab) are found in about 40% of children with first demyelinating event in particular acute demyelinating encephalomyelitis (ADEM).1, , , –5 In adults, MOG antibodies are described in about 30-50% of patients suffering from Aquaporin-4 antibody (AQP4-Ab) seronegative Neuromyelitis optica spectrum disorders (NMOSD).6, , , , –11 Here, NMOSD overlaps with the spectrum of MOG-AD.11,12 However, among patients with MOG-AD, only 23% of adults and 31% of children fulfill diagnostic criteria for seronegative NMOSD.11 Multiple clinical, radiologic differences exist.