AQP4 and neuromyelitis optica: Clinically it may mimic aquaporin 4 (AQP4)‐antibody‐associated disease as a neuromyelitis optica (NMO) spectrum phenotype, with optic neuritis being the commonest onset and relapse presentation, but particularly in children may present as an acute demyelinating encephalomyelitis (ADEM), and more rarely as a cortical syndrome with seizures.