Challenge 1 group included 28 patients with positive MOG-IgG results, of whom 21 (75%; 12 with clear-positive and 9 with low-positive results) received MS diagnosis, 2 (7%; 1 with clear-positive and 1 with low-positive results) MOGAD diagnosis, and 5 (18%; 2 with clear-positive and 3 with low-positive results) discordant diagnoses. The gene discussed is MOG; the disease is myeloid sarcoma.