This is the "major histocompatibility complex, class II, DR alpha" gene. It is also known as HLA-DRA1. It plays a central role in the immune system by presenting peptides derived from extracellular proteins.
HLA-DRA codes for the alpha subunit of the HLA DR loci, and is largely invariant. The variation in HLA-DR comes from the beta units, which is important for organ compatibility.
The DRA SNP A/G rs3135388 is a proxy for the DRB1*1501 allele, which is associated with MS. Concordance between the rs3135388 A allele and DRB1*1501 was found in 2730 of 2757 subjects by the International Multiple Sclerosis Genetics Consortium (2007).
For a full list of HLA gene SNPs, see the HLA page.