HLA-DRB1 and neuromyelitis optica: Two studies showed a significant difference between the frequency of the DRB1*03 allele group and the DRB1*15:01 allele (Ribeirão Preto (SP)25—DRB1*03: 24.07%-NMO vs 8.62%-MS, pcF = 0.0254; DRB1*15: 3.7%-NMO vs 37.9%-MS, pcF = 0.0001 and Rio de Janeiro33—DRB1*03:01: 20%-NMO vs 6.4%-MS, pcF ≤ 0.001; DRB1*15:01: 2.3%-NMO vs 15.4%-MS, pcF ≤ 0.001).