Altered tertiary structure or loss of arginines in portions of fibronectin not yet recognized to be involved with synovial fibroblast adhesion may be the most probable explanation for the observed cellular defects on citrullinated fibronectin since, to date, only five arginines in human fibronectin purified from the synovial fluid of two people with rheumatoid arthritis have been identified as citrullinated [40], none of which are in the RGD domain or the heparan sulfate binding domain. The gene discussed is FN1; the disease is rheumatoid arthritis.