A single nucleotide polymorphism (SNP) within the gene locus encoding protein tyrosine phosphatase non-receptor type 22 (PTPN22; SNP ID rs2476601) has been associated with an increased risk to develop autoimmune disorders, including rheumatoid arthritis (RA)[1–3], systemic lupus erythematosus (SLE)[4–6], Graves disease[7], and type-I diabetes (T1D)[7, 8]. The gene discussed is PTPN22; the disease is rheumatoid arthritis.