HLA-DRB1 and myeloid sarcoma: The frequency for the homozygous HLA DRB1*1501 positive, heterozygous and homozygous HLA DRB1*1501 negative genotypes in MS patients were 18.7%, 33.2%, and 48.1%, respectively; the corresponding frequencies of these genotypes in controls were 5.8%, 25.8%, and 68.4%, respectively (chi-square = 20.6, p<0.001).