HLA-DRB1 and rheumatoid arthritis: The valine or leucine residue at position 11 within the HLA-DRB1 protein (i.e., HLA-DRB1 Val11 and HLA-DRB1 Leu11) is associated, predominately in the Caucasian and Spanish populations, with increased risk of severe radiographic progression in ACPA-positive RA, independent of HLA-DRB1 SE status [38].