HAE has classically been described as occurring due to a deficiency of functional C1 inhibitor (C1INH, HAE‐C1INH): HAE‐C1INH‐Type1 is caused by deficient plasma levels of C1INH (∼85% of HAE‐C1INH cases), and patients with HAE‐C1INH‐Type2 have normal plasma levels but dysfunctional C1INH (∼15% of HAE‐C1INH cases) [2]. This evidence concerns the gene SERPING1 and hereditary angioedema.