Such a diagnosis can be made in a patient seronegative for AQP4-IgG when at least two core clinical features occur as a consequence of one or more clinical attacks, and all of the following conditions are met: (a) at least one core clinical feature must be NMO-typical (optic neuritis, acute myelitis with longitudinally extensive transverse myelitis (LETM) or area postrema syndrome); (b) clinically proven dissemination in space (two or more different core clinical syndromes) with additional MRI requirements specific for each clinical syndrome (see Figure 1) [8]. The gene discussed is AQP4; the disease is neuromyelitis optica.