First, certain clinical features, laboratory findings, and/or prognostic characteristics differ between AQP4-IgG-positive and AQP4-IgG-negative patients [1,99,101,104,109], among the various NMO-SD (as shown for time-to-relapse, prognostic implications of clinical presentation at onset, and CSF findings [1,110]), and between patients with monophasic disease and patients with relapsing disease [1,2]. This evidence concerns the gene AQP4 and neuromyelitis optica.