HLA-DRB1 and myeloid sarcoma: To exclude the possibility that the HLA-DPB1 susceptibility signal may derive from the primary HLA-DRB1*15:01 association, we performed a stratification analysis, which excluded families and individuals that carried the haplotype bearing HLA-DRB1*15:01, confirming that HLA-DPB1*104:01 is independently associated with MS risk (Supplemental Table 4B).