Gender differences in primary antiphospholipid syndrome with vascular manifestations in 433 patients from four European centres

Objectives: Gender can influence incidence and clinical course of autoimmune diseases (ADs). Antiphospholipid syndrome (APS) is a rare AD characterised by thromboses and/or pregnancy morbidities and antiphospholipid antibodies (aPL) positivity. Our aim is to conduct a gender-oriented analysis of primary thrombotic APS (t-APS). Methods: Consecutive patients diagnosed with primary t-APS, followed from 1967 to 2019 in four European Centres, were enrolled. Results: The cohort included 296 women and 137 men. Median age at onset [31 (24-46) vs. 41 (29-53) years, p<0.001] was lower in females. In women, venous thromboses were more frequent while, among males, arterial events prevailed. During follow-up, 14% of patients suffered at least two relapses and this occurred especially among males (22% vs. 10%, p=0.001). No gender differences were found in the aPL profile (33% single, 24% double and 43% triple aPL positivity). Most patients had concomitant risk factors (RFs) for thrombosis: established cardiovascular RFs were represented especially among men while estrogenic exposure was the main RF in women. Conclusions: Women presented mostly with venous thromboses at a younger age, while men with arterial events, later in life and suffered more recurrent events. This different frequency of arterial and venous thromboses could be attributed mainly to the presence of additional RFs rather than to biological gender-specific issues. However, some RFs are exclusive or more represented in one gender rather than the other, so assessing the link of causality between gender and manifestations of t-APS remains difficult.