The HLA-DRB1*15 allele provides an increased risk of MS with an odds ratio (OR) of approximately 3 whereas the HLA-A*02 allele of the HLA-A locus exerts a protective effect with an OR of approximately 0.5.1,2 Although predisposing gene variations have a role in disease development, previous estimations of the heritability may have been overestimated. The gene discussed is HLA-A; the disease is myeloid sarcoma.