STAT4 and rheumatoid arthritis: 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