Its presence should alert the physician to alternative diagnoses, which could comprise life-threatening conditions that are refractory to the usual first-line treatments in the emergency room (i.e., antihistamines, corticosteroids, epinephrine), including hereditary angioedema (HAE), acquired angioedema (AAE), or angioedema associated with angiotensin-converting enzyme (ACE) inhibitors. This evidence concerns the gene ACE and angioedema.