Methods: AQP4-antibody seronegative patients presenting 2005–2016 with CNS inflammatory disease suspicious for NMOSD, as well as 20 MS controls, were retrospectively tested for MOG-IgG1 antibodies by live cell-based assay at Oxford Autoimmune Neurology Diagnostic Laboratory (UK) and by a commercial fixed cell-based assay at MitogenDx (Calgary, Canada). The gene discussed is AQP4; the disease is myeloid sarcoma.