The demonstration of AQP4‐specific immunoglobulin G (IgG) autoantibodies (NMO‐IgG) in NMO patients (Lennon, Kryzer, Pittock, Verkman, & Hinson, 2005; Lennon et al., 2004), and its pathogenicity (Saadoun et al., 2010; Tradtrantip et al., 2012) provides further evidence. The gene discussed is AQP4; the disease is neuromyelitis optica.