These SLE susceptibility genes could affect different steps of SLE development including B cell tolerance breakdown leading to autoantibody production (e.g., PTPN22, BANK1, BLK, LYN), defective clearance of immune complexes and apoptotic debris (e.g., ITGAM, Fc gamma R, Complement), T cell activation (e.g., PTPN22, CTLA4) or organ damage (e.g., Complement, IRF5, TNFAIP3) 1,2. The gene discussed is PTPN22; the disease is systemic lupus erythematosus.