Increased risk of venous thromboembolism in young and middle-aged individuals with hereditary angioedema: a family study.

Hereditary angioedema (HAE) due to C1 inhibitor protein (C1-INH) deficiency was recently shown to be associated with increased risk of venous thromboembolism (VTE). This is the first national family study of HAE with the aim to determine the familial risk of VTE. The Swedish Multi-Generation Register was linked to the Swedish National Patient Register during the period 1964-2018. Only HAE patients with a validated diagnosis were included in the study and were linked to their family members. Hazard ratios (HRs) and 95% confidence intervals (CIs) for VTE were calculated for HAE patients compared with relatives without HAE. Among 2,006 individuals (from 276 pedigrees of 365 patients with HAE), 103 individuals were affected by VTE. In total 35 (9.6%) of HAE patients compared to 68 (4.1%) of non-HAE relatives were affected by VTE (p<0.001). The adjusted HR for VTE among HAE patients was 2.51 (95% CI 1.67-3.77). HAE patients were younger at the first VTE than their non-HAE relatives (mean age 51 versus 63 years, p<0.001). Before the age of 70 years the HR for VTE among HAE patients was 3.62 (95%CI 2.26-5.80). The HR for VTE for HAE patients born after 1964 was 8.29 (95%CI 2.90-23.71). The HR for VTE for HAE patients born 1964 or earlier was 1.82 (95%CI 1.14-2.91). HAE is associated with VTE among young and middle-aged individuals in Swedish families with HAE. The effect size of the association is in the order of other thrombophilias. We suggest that HAE may be considered a new rare thrombophilia.