COL18A1 and hereditary angioedema: Less frequently, patients with HAE may have normal C1‐INH quantity and function and no mutation in the SERPING1 gene – this is known as HAE with normal C1 inhibitor (nC1‐INH‐HAE) and is caused by mutations in one of several different genes, including but not limited to genes coding for coagulation factor XII, plasminogen, and angiopoietin‐1 (Table 1).3