AQP4 and neuromyelitis optica: Interestingly, in the European GWAS, the HLA-DRB1*03:01 allele was imputed and found to be associated with AQP4-IgG-seropositive NMO but not with AQP4-IgG-seronegative NMO, and showed a high correlation with rs1150757 (r2 = 0.7) but a poor correlation with rs28383224 (r2 = 0.2)16.