HLA-DRB1 and rheumatoid arthritis: Sixty percent of those with RA have been found to have polymorphisms in HLA-DRB1 with a shared epitope in the hypervariable region of DRB1, leading to poor T cell antigen presentation, along with a smaller subset who present with epigenetic changes, such as PTPN11 hypermethylation, promoting the overexpression of fibroblast-like synoviocytes [90].