AQP4 and myeloid sarcoma: The proportion of AQP4-ON (USA and Europe: 0–5.8%, China: 20–43.5%, South Korea:14.3–37.8%, Japan: 3.4–12.4%) or MOG-ON (USA and Europe: 1.7–13.8%, China: 14.4–21.8%, Japan: 10.2–25.7%) among all ON cases appears to be much higher in Asian populations than in white Caucasians from Europe and North America, and appears to correlate with a lower prevalence of MS in these regions [1, 2, 39].