AQP4 and neuromyelitis optica: Most importantly, since 75% of seronegative patients developed MOG-ab within four months of neurological disease onset in Tanaka’s study (Tanaka and Tanaka, 2014), and 100% of AQP4-ab sero-negative patients developed MOG-ab at the time of disease onset in Kitley’s study (Kitley et al., 2014), the suggestion that MOG-Ab in NMO does not emerge from secondary demyelination seems logical.