Factor XII autoantibodies as a novel marker for thrombosis and adverse obstetric history in patients with systemic lupus erythematosus

Aim: To investigate the clinical significance of anti- factor XII ( FXII) in a large cohort of patients with systemic lupus erythematosus ( SLE). Patients and methods: This study comprised 127 patients with SLE. IgG and IgM anti- FXII were tested by an in- house ELISA. 123 healthy donors comprised the control group. Results: 51 ( 40%) patients with SLE and 9 ( 7%) healthy controls were positive for anti- FXII. IgG and IgM anti- FXII were frequently found in patients with thrombosis ( 28% and 13%, respectively). Levels of IgG and IgM anti- FXII were higher in patients with thrombosis than in the control group ( p < 0.001 and p = 0.005, respectively). Anti- FXII was more frequent in patients with arterial thrombosis ( 31% vs 4% for IgG and 14% vs 3% for IgM, respectively) and venous thrombosis than in controls ( 37% vs 4% for IgG). IgG anti- FXII were more frequent in patients with miscarriages and fetal death ( 35% and 40% vs 4% for IgM). The prevalence of IgM anti- FXII was not different between groups. Conclusion: Anti- FXII are frequent in patients with SLE. Their presence is associated with thrombosis and adverse obstetric history, making these antibodies a novel marker for the antiphospholipid syndrome.