More broadly, those criteria should be primarily used to make, rather than to exclude, a diagnosis of NMO, because brain lesions and (far more rarely) short spinal cord lesions—individually or combined—may in fact be present in patients with otherwise typical NMO (as confirmed by AQP4-Ab seropositivity and/or occurrence of longitudinal extensive transverse myelitis (LETM) in the later disease course in these patients) [1]. The gene discussed is AQP4; the disease is neuromyelitis optica.