Hereditary angioedema: Classification, pathogenesis, and diagnosis

Hereditary angioedema (HAE) is a rare autosomal dominant genetic disorder associated with a deficiency in C1 inhibitor. More than 200 mutations in this gene, located on chromosome 11, have been identified. Although HAE is often inherited, 20‐25% of cases are from new spontaneous mutations and they have no family history of swelling. Decreased C1 inhibitor activity leads to inappropriate activation of multiple pathways, including the complement and contact systems and the fibrinolysis and coagulation systems. Reduced C1 inhibitor activity results in increased activation of plasma kallikrein-kinin system proteases and increased bradykinin levels. Bradykinin is felt to be the main mediator of symptoms in HAE. Patients with HAE have recurrent episodes of swelling of the extremities, abdomen, face, and upper airway. Angioedema involving the gastrointestinal tract can lead to intestinal wall edema, which results in abdominal pain, nausea, vomiting, and diarrhea. Laryngeal swelling is life-threatening and may lead to asphyxia. Common triggers of an attack include trauma, stress, infection, menstruation, oral contraceptives, hormone replacement therapy, and angiotensin-converting enzyme inhibitors. Laboratory testing including C4, C1 inhibitor level, and function is needed to confirm or rule out the diagnosis of HAE. The treatment of HAE has improved significantly in recent years with the availability of several safe and effective therapies. Several consensus guidelines have been created to further assist in the management of HAE patients. This review will provide an update on the classification, pathophysiology, clinical presentation, and diagnosis of HAE.