AQP4 and intervertebral disk degenerative disorder: NMOSD was initially thought to be more common than MOG-EM/MOGAD among adult patients with IDD [55, 106] and less frequent than MOG-EM/MOGAD among children with IDD [15, 34, 188]; however, recent data suggest that cases of MOG-EM/MOGAD may outnumber those of both AQP4-IgG-positive and AQP4-IgG-negative NMOSD also in adults, in both Asian and non-Asian populations [121, 188].