In HLA-DRB1 analyses, HLA-DRB1*15∶01 was a stronger risk factor for OCB-positive than OCB-negative MS, whereas HLA-DRB1*04∶04 was associated with an increased risk of OCB-negative MS and a reduced risk of OCB-positive MS. This evidence concerns the gene HLA-DRB1 and myeloid sarcoma.