Our observations that NMO/NMOSD associated with MOG-ab characterized cardinal clinical and MRI features that are independent and distinct from those of AQP4-ab (Kitley et al., 2014; Kitley et al., 2012; Mader et al., 2011; Rostasy et al., 2013; Sato et al., 2014; Tanaka and Tanaka, 2014) suggest two possibilities. Here, AQP4 is linked to neuromyelitis optica.