PTPN22 and rheumatoid arthritis: Thus, the previous observation of stronger association of HLA-B8 with women in MG [15], [34] extends to another locus, PTPN22. This difference of PTPN22 in women and men was not observed previously in the genome-wide association study [15], but similar findings have been proposed previously in rheumatoid arthritis (RA) for PTPN22[28], [35].