It is important to note that although HLA-DRB1*04 and HLA-DRB1*01 are often grouped together as SE-containing serotypes, we chose to separate them in our analysis, since the association of HLA-DRB1*04 with RA is considerably stronger than that of HLA-DRB1*01 (12). This evidence concerns the gene HLA-DRB1 and rheumatoid arthritis.