Genetic factors associated with MS risk are mainly major histocompatibility class II (MHC II) alleles (e.g., HLA-DRB1*15:01, the earliest identified and most dominant risk factor in MS) and MHC I alleles (e.g., HLA-A*02 and HLA B*44, decreasing MS susceptibility). The gene discussed is HLA-A; the disease is myeloid sarcoma.