Episodes of ON (unilateral or bilateral) all preceded initial myelitis presentations, with ON in 9 (45%) of 20 patients with AQP4-IgG seropositive NMOSD vs 1 (6%) of 17 “double-seronegative” patients (p = 0.011) and 1 (33%) of 3 patients with MOGAD (Table 1). This evidence concerns the gene AQP4 and myelitis.