PTPN22 and systemic lupus erythematosus: Further, trimethylation of histone H3 at lysine 4 (H3K4) molecules at PTPN22 (protein tyrosine phosphatase, non-receptor type 22) and LRP1B (LDL receptor related protein 1B) genes positively correlate with lupus severity and is annotated as “histone modification” (VariO:0453).