PTPN22 and rheumatoid arthritis: Recently convincing proof of this hypothesis has been provided by the association of the missense single nucleotide polymorphism (SNP; rs2476601) in the protein tyrosine phosphatase N22 (PTPN22) gene with at least five autoimmune diseases; RA [3,4], SLE [5], autoimmune thyroid disease [6], T1D [7] and juvenile idiopathic arthritis [4].