Genome-wide association studies identified variants in the gene locus encoding protein tyrosine phosphatase nonreceptor type 2 (PTPN2; also known as T cell protein tyrosine phosphatase (TCPTP)) to be associated with IBD, as well as with other chronic inflammatory diseases, including type 1-diabetes, rheumatoid arthritis, and celiac disease [2,3,4]. Here, PTPN2 is linked to rheumatoid arthritis.