PTPN2 and psoriasis: Genome-wide association studies (GWAS) identified variants within the gene locus encoding protein tyrosine phosphatase non-receptor type 2 (PTPN2; also known as T cell protein tyrosine phosphatase [TC-PTP]) to be associated with chronic inflammatory and autoimmune diseases, including type 1-diabetes, psoriasis, rheumatoid arthritis, systemic lupus erythematosus, Crohn's disease, and celiac disease (3–5).