In this phase 3 double-blind trial, patients with NMO-SD and AQP4 seropositivity, with an EDSS score of 7.0 or less, were randomly assigned (2:1) treatment with eculizumab (IV, every week for the first four doses, followed by every 2-weeks; n = 96) or placebo (matched administration; n = 47). This evidence concerns the gene AQP4 and neuromyelitis optica.