To screen for possible functional or causative variants in the AQP4, AQP1 and MOG genes, we sequenced all exons of the three genes in 18 NMOsd Spanish patients (12 seropositive and 6 seronegative for anti-AQP4 IgG) and in 16 MS patients for comparative purposes. The gene discussed is AQP4; the disease is myeloid sarcoma.