HLA-DRB1 and neuromyelitis optica: A meta-analysis with the results of the thirteen studies that investigated the association of the DRB1*03:01 allele with NMO is summarized at the forest plot (Fig. 2), indicating that patients with NMO are 2.46 times more likely to have the DRB1*03 allele group than controls (95% CI 2.01—3.01).