A highly attractive candidate gene for IBD, owing to its anti-inflammatory function and involvement in type 1 diabetes susceptibility and rheumatoid arthritis [29], is the PTPN2 (protein tyrosine phosphatase, non-receptor type 2) located on chromosome 18p11, which encodes for a tyrosine phosphatase expressed in T cells, a negative regulator of inflammation. The gene discussed is PTPN2; the disease is rheumatoid arthritis.