PTPN22 and systemic lupus erythematosus: GWAS found an association of PTPN22 1858T with seropositive SLE in a case-only analysis and another study found a positive association with anti-cardiolipin IgG and a trend towards an increased frequency of PTPN22 1858T in patients with lupus nephritis or in individuals seropositive for anti-dsDNA autoantibodies [55,56].