The possibility that both HLA-DRB1*1501 and HLA-DQB1*0602 loci influence susceptibility to MS through epistatic interactions has been demonstrated in Canadian MS cohorts, where the HLA-DQA1*0102, which showed no independent association, was found to interact strongly with HLA-DRB1*1501 in trans, increasing MS risk in the presence of HLA-DRB1*1501 and playing a protective role in its absence [45]. This evidence concerns the gene HLA-DQB1 and myeloid sarcoma.