PTPN22 and rheumatoid arthritis: Possible reasons for the association between systemic ANCA associated vasculitis and RA may be the common genetic predispositions to autoimmunity which involve the HLA region or genes such as PTPN22, reported in series of both RA and AAV (Jagiello et al. 2005; Farago et al. 2009; Johansson et al. 2006; Lee et al. 2005).