APS IgG significantly reduced FXa activity (P < 0.0001 for APS versus HC, and P = 0.0008 for APS versus SLE IgG) and antithrombin-III mediated inhibition of FXa activity (P < 0.0001 for APS versus SLE and APS versus HC IgG) and significantly prolonged the clotting time compared to HC IgG (p < 0.0001) and SLE/APS- IgG (p = 0.04). The gene discussed is SERPINC1; the disease is autoimmune polyendocrinopathy.