Multiple studies have demonstrated that NMO-IgG does not directly interfere with the water permeability of AQP4 [90,91,92], probably because NMO-IgG cannot access all four monomers—each of which has a water pore—because of the large size of immunoglobulin compared to the tetrameric composition of AQP4, as Rossi et al. pointed out [91]. Here, AQP4 is linked to neuromyelitis optica.