HLA-DRB1 and rheumatoid arthritis: One example is the strong association between RA and HLA-DRB1 alleles that contain the so-called “shared epitope” (Gregersen et al, 1987; van Drongelen and Holoshitz, 2017), a 5-amino-acid sequence in the HLA-DRB1 molecule that is associated with RA.