Although some cases of MOG-IgG positive patients fulfill the diagnostic criteria of neuromyelitis optica spectrum disorders (NMOSD), multiple sclerosis (MS), acute disseminated encephalomyelitis (ADEM), or other idiopathic inflammatory demyelinating diseases (IIDDs), there are no distinct types of IIDDs that can explain all presentations of MOG-IgG positive patients. The gene discussed is MOG; the disease is myeloid sarcoma.