While this approach seems to offer simplicity, it would be inappropriate for several reasons: (1) The IPND criteria for AQP4-IgG-negative NMOSD demand dissemination in space, which would prevent testing of many patients with syndromes compatible with MOG-EM (e.g., patients with isolated longitudinally extensive transverse myelitis [LETM], isolated bilateral ON, or isolated brainstem encephalitis). The gene discussed is AQP4; the disease is transverse myelitis.