PTPN22 and systemic lupus erythematosus: PTPN22 has been shown to be one of the strongest non-HLA susceptibility genes for various autoimmune diseases, such as rheumatoid arthritis (RA), type 1diabetes (T1D), systemic lupus erythematosus (SLE), and Graves' disease (GD) [18], [19], [20], [21], [22].