Genetic factors, especially MHC II alleles carrying a “shared epitope” motif, were originally described to be associated with RA, although other genes such as peptidyl arginine deiminase (PAD) and protein tyrosine phosphatase non-receptor 22 (PTPN22) have been suggested to be associated with RA onset as well [12,128,130,132,133,134]. The gene discussed is PTPN22; the disease is rheumatoid arthritis.