Much evidence has implicated four of the proteins (CCN1, CCN2, CCN3 and CCN4) in the inflammatory pathologies of RA [10,11,12,13] and OA [14,15,16,17,18,19,20]; the evidence base is smaller for CCN5 and CCN6 in these diseases [21,22,23,24]. Here, CCN1 is linked to rheumatoid arthritis.