We found that the presence of 2 T risk alleles of rs12537 in the miR-181a -binding site in the 3′UTR of MTMR3 was a candidate for increased risk and severity of both RA and SLE among Egyptian patients recruited in this study, indicating a novel role of this SNP in the genesis and progression of both diseases. Here, MTMR3 is linked to rheumatoid arthritis.