CTLA4 and rheumatoid arthritis: Current genome-wide association studies (GWASs) have identified 46 genetic loci, such as HLA, PTPN22, and CTLA4 associated with RA [2]; however, the identified risk loci of RA have modest effect sizes (odds ratios in the range of 0.78 to 2.78) and can explain only about 16% of the RA heritability [3].