The second-generation individual H0278DC4 diagnosed with MS inherited both, the protective HLA-B*27:02:01 allele and the high-risk HLA-DRB5*01:01:01~HLA-DRB1*15:01:01:01 haplotype block, further exemplifying the limited penetrance of protective and risk alleles and complex interaction underlying the association signals. The gene discussed is HLA-DRB5; the disease is myeloid sarcoma.