In particular, we have found significantly lower frequencies of CSF-restricted oligoclonal bands (OCB) and other markers of intrathecal IgG synthesis in patients with AQP4-IgG-positive neuromyelitis optica (NMO) spectrum disorders (NMOSD), myelin oligodendrocyte glycoprotein antibody-associated encephalomyelitis (MOG-EM), acute demyelinating encephalomyelitis (ADEM) and paraneoplastic neurological disorders (PND) than in MS, as well as significant differences in intrathecal IgG composition and dynamics and in blood–CSF barrier function [3–14]. The gene discussed is AQP4; the disease is myeloid sarcoma.