Among patients with rheumatoid arthritis (RA), the reported prevalence of AITD is increased, although the reported levels of increase vary with study design, geographical region, and the definition of AITD.2,3,4,5,6,7 Variants in genes (eg, PTPN22, CTLA 4, and HLA-DR) involved in the regulation of T-cell response have been associated with both RA and AITD, suggesting that shared inheritance may be one factor linking the 2 conditions together. Here, PTPN22 is linked to rheumatoid arthritis.