PTPN22 and rheumatoid arthritis: In genome-wide associations studies (GWAS), the single nucleotide polymorphism (SNP) rs2476601 within the PTPN22 locus was identified to increase the risk for autoimmune disorders such as type 1 diabetes (T1D) [82], rheumatoid arthritis (RA) [83], systemic lupus erythematosus [84,85] and Graves’ disease [86].