PTPN22 and rheumatoid arthritis: Furthermore, in the presence of allele C, the DCIR expression was higher in both ACPA-positive and ACPA-negative RA subsets, though being unable to reach the statistical significance in ACPA-negative RA due to the loss of statistical power, indicating rs2377422 might interact with other risk factor(s) to contribute specifically to ACPA-negative RA, as the contribution of PTPN22 to ACPA-positive RA [4].