Background and objectives: Rheumatoid arthritis (RA) is an autoimmune disease with a complex genetic background. The protein tyrosine phosphatase non-receptor type 22 (PTPN22) is a lymphoid specific protein tyrosine phosphatase which is involved in negative regulation of T cell response. Several studies have assessed the association between PTPN22 single nucleotide polymorphisms (SNPs) with RA ...