Consistent with the findings from haplotype inheritance analyses, the effect of MS associated DRB1-DQB1 genotypes delineates a model constituted by a dominantly acting susceptibility gene contained on, or near to, the *04:05-*03:01, *13:03-*03:01, *03:01-*02:01 haplotypes, in conjunction with the absence of a protective gene required for the maintenance of peripheral tolerance. Here, HLA-DRB1 is linked to myeloid sarcoma.