PRB2 and systemic lupus erythematosus: IgG anti-PS/FXa positivity was found more frequently (P <0.05) in patients with the SLE/APS- (n = 35, 33%) compared with APS (n = 8, 13.6%), Myo (n = 1, 4.3%), SSc (n = 0) and HC (n = 0) groups.