PTPN22 and rheumatoid arthritis: Despite differences in the genetic backgrounds of RA patients, the significance of the HLA-DRB1-shared epitope (6p21.3) [10], [11], [12], [13] and PTPN22 (1p13.3-p13.1) [14], [15], [16], [17], [18], [19], [20] in the genomes of RA patients has been well replicated in different genetic studies.