In Mexicans, we found a high frequency of some MHC class II alleles that predispose to rheumatoid arthritis (RA) (DRB1*04∶04, DRB1*14∶02, and DRB1*01∶02), to systemic lupus erythematosus (SLE) (DRB1*03∶01) [11] and to systemic sclerosis (SSc) (DRB1*11∶04) (Rodriguez-Reyna TS et al., Unpublished data). This evidence concerns the gene HLA-DRB1 and systemic lupus erythematosus.