In the case of the IgA isotype, all groups of patients present higher levels of Anti-CD26 aAbs than healthy donors (Table 1 and Fig. 1), with the highest values found in RA and CG patients; in these two groups of patients, IgA Anti-CD26 aAbs values were around 5- and tenfold higher than those of the other patient groups and healthy donors, respectively. This evidence concerns the gene DPP4 and rheumatoid arthritis.