CTLA4 and rheumatoid arthritis: Population-based differences in susceptibility to RA are observed through previous reports that show an association between RA and rs3087243 (+60C/T), a polymorphism known to affect the expression levels of soluble CTLA4 protein [35], in Swedish and North-American populations [14] or a lack of association at this locus in studies based in Massachusetts or Northern Ireland [7],[13].