The single-nucleotide polymorphism (SNP) R620W, also denoted rs2476601, is located within the hematopoietic-specific protein tyrosine phosphatase gene, PTPN22. This SNP (C/T) codes for an amino-acid change and the frequency of its minor allele T has been recently and repeatedly shown to be increased in patients with rheumatoid arthritis (RA) [1]. The gene discussed is PTPN22; the disease is rheumatoid arthritis.