PTPN22 and rheumatoid arthritis: Increasing evidence indicates that autoimmune diseases such as SLE, RA and Crohn’s disease share common risk genes with Behcet’s disease and VKH, including genes such as interleukin-23 receptor(IL23R) [18]–[20], protein tyrosine phosphatase non-receptor type 22 (PTPN22) [21]–[23] and signal transducer and activator of transcription 4 (STAT4) [24]–[25].