This is supported by studies reporting an association between earlier MS onset and both HLA-DRB1*15:01, the primary MS risk allele, and a higher genetic risk score of ∼200 nonmajor histocompatibility complex (MHC) MS risk variants.10, -, 12 There have been 2 large, published genome-wide association studies (GWAS) for MS AAO. The gene discussed is HLA-DRB1; the disease is myeloid sarcoma.