The remarkable LD between these genes makes it difficult to determine by genetic studies whether the functionally relevant effect on MS derives from DRB1*15:01 only, or also from its neighboring DQA1*01:02-DQB1*06:02 or DRB5*01:01 genes of HLA-DR15 haplotype. This evidence concerns the gene HLA-DQA1 and myeloid sarcoma.