Linkage studies of families with multiple affected members with MS show that variation within the human leukocyte antigen (HLA) class II locus on chromosome 6p21 is associated with an increased risk of MS, with the main risk allele, HLA-DRB1*15:01, carrying an average odds ratio of 3.08 (Bertrams & Kuwert, 1976; Hollenbach & Oksenberg, 2015). The gene discussed is HLA-DRB1; the disease is myeloid sarcoma.