The rs7426056 CD28 genetic variant is located 3.5 kb downstream of the CD28 3′UTR and approximately 120 kb upstream of CTLA4. It is in almost complete linkage disequilibrium (r2 = 0.99) (https://caprica.genetics.kcl.ac.uk/~ilori/ld_calculator.php) with the genetic variant rs1980422, also within the CD28 locus, that has been associated with rheumatoid arthritis locus4. Here, CTLA4 is linked to rheumatoid arthritis.