By comparing the ratio of expression (Figure 2), we found that PTPN22 expression in RA cases is significantly different compared with that in controls (P = 6 × 10-9), which is a result of significantly higher expression of PTPN22-long isoforms and simultaneously slightly lower expression of PTPN22_v4 in patients (Table 1). Here, PTPN22 is linked to rheumatoid arthritis.