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Abstract: Hereditary angioedema (HAE), caused by C1 inhibitor protein deficiency, was recently shown to be associated with an increased risk for venous thromboembolism (VTE). To our knowledge, this is the first national family study of HAE, which aimed to determine the familial risk of VTE. The Swedish Multi-Generation Register was linked to the Swedish National Patient Register for the period of 1964 to 2018. Only patients with HAE 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 patients with HAE in comparison with relatives without HAE. Among 2006 individuals (from 276 pedigrees of 365 patients with HAE), 103 individuals were affected by VTE. In total, 35 (9.6%) patients with HAE were affected by VTE, whereas 68 (4.1%) non-HAE relatives were affected (P < .001). The adjusted HR for VTE among patients with HAE was 2.51 (95% CI, 1.67-3.77). Patients with HAE were younger at the first VTE than their non-HAE relatives (mean age, 51 years vs 63 years; P < .001). Before the age of 70 years, the HR for VTE among patients with HAE was 3.62 (95% CI, 2.26-5.80). The HR for VTE for patients with HAE born after 1964 was 8.29 (95% CI, 2.90-23.71). The HR for VTE for patients with HAE who were born in 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., (© 2024 American Society of Hematology. Published by Elsevier Inc. All rights are reserved, including those for text and data mining, AI training, and similar technologies.)