PTPN22 and systemic lupus erythematosus: Recent genome-wide association studies revealed that certain gene loci, including the R620W polymorphism of the protein tyrosine phosphatase PTPN22 and the interferon induced with helicase C domain 1 (IFIH1) rs1990760 polymorphism, are associated with susceptibility to multiple autoimmune diseases including Graves’ disease, Hashimoto’s thyroiditis, and SLE [25, 26].