To investigate whether there are genetic differences between AQP4-IgG antibody seropositive and seronegative NMO cases, we stratified our analyses into three categories: AQP4-IgG-seropositive NMO (NMO-IgG+), AQP4-IgG-seronegative NMO (NMO-IgG−), and combined NMO irrespective of AQP4-IgG status (NMO) (Fig. 1). Here, AQP4 is linked to neuromyelitis optica.