Polymorphic variants of the tyrosine phosphatase non-receptor type 22 (PTPN22) gene, the Cytotoxic T-Lymphocyte Associated Protein 4 (CTLA4), the signal Transducer and Activator of Transcription 4 (STAT4), and variants of the genes that encode enzymes peptidylarginine deiminases (PADI)-2 and PADI-4 have been associated with susceptibility to RA.51–53 Still, differences in the genetic factors related to RA susceptibility have been identified between different populations in Europe, Asia, and Africa.54,55. Here, PTPN22 is linked to rheumatoid arthritis.