Second, treatment strategies might differ between AQP4-IgG-positive and AQP4-IgG-negative patients (taking into account possible differences in aetiology and pathogenesis), even among NMO-SD (e.g. based on differences as to time-to-relapse and short-term prognosis [1]), and between patients with monophasic and patients with relapsing NMO-SD (which could well be manifestations of different diseases, e.g. postinfectious ADEM vs. AQP4 autoimmunity). The gene discussed is AQP4; the disease is Salla disease.