Hereditary angioedema due to C1 inhibitor deficiency (HAE-C1-INH) is an autosomal dominant disease with an estimated prevalence of 1:50,000 [2] and is caused by mutations in the SERPING1 gene, which codes for C1 esterase inhibitor (a serine protease inhibitor) [3]. Here, C1S is linked to hereditary angioedema.