HLA-DRB1 and rheumatoid arthritis: An extensive meta-analysis on the influence of multiple HLA alleles has shown that despite these categories, HLA-DRB1*13:01, and to a lesser extent HLA-DRB1*13:02, confers protection in ACPA+ RA but not ACPA− RA in four different populations (Salvat et al. 1994; van der Woude et al. 2010a).