Most of the previous studies, based on the common classification, identified HLA-DRB1*101, HLA-DRB1*0401, HLA-DRB1*404 and HLA-DRB1*1001 as predisposing alleles for ACPA production in RA, with a significant dose effect in patients carrying two of these predisposing alleles [9,12,32,44]. This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.