In a Canadian report, the HLA-DRB1 allele frequencies were compared between mild (RRMS with EDSS ≤ 3 over a period >20 years) and malignant (PPMS or RPMS with EDSS > 6 within 5 years of disease onset) MS cases. The gene discussed is HLA-DRB1; the disease is myeloid sarcoma.