HLA-DR51 is a HLA-DR serotype that recognizes the antigens encoded by the minor DR locus HLA-DRB5.
DRB3, DRB4, and DRB5 are minor DR beta encoding loci, they have been recognized as having distinct evolution,[1] having diverged from DRB1 approximately 4 million years ago.
[2] DRB5 locus is only apparent in a small subset of DR haplotypes, and most individuals lack DRB5.
B5*02 encoded 4 alleles that can generate 4 isoforms.
There are numerous null genes at this locus.