The prevalence of MOG-IgG seropositivity among patients with NMOSD or limited forms has been reported by several studies and varies widely, depending mainly on each sample’s inclusion criteria (for example, children and/or adults; diagnosed based on 2006 criteria for NMO or 2015 criteria for NMOSD, etc.)but also on the detection technique used in each study. The gene discussed is MOG; the disease is neuromyelitis optica.