DSG1 and rheumatoid arthritis: Autoantibodies for this study included antinuclear antibodies (AN-Abs); antibodies to extractable nuclear antigens (ENA-Abs, including smooth muscle (Sm-Ab), ribonucleoprotein (RNP-Ab), SSA/Ro-Ab, and SSB/La-Ab) for systemic lupus erythematosus, Sjögren's syndrome, and other connective tissue diseases; antibodies to the cyclic citrullinated peptide (CCP-Abs) for rheumatoid arthritis; antibodies to tissue transglutaminase (tTGM-Abs) for celiac disease; antibodies to the 180 kDa bullous pemphigoid antigen (BP180-Abs); and antibodies to desmoglein 1 (Dsg1-Abs) and Dsg3-Abs respectively.