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Hereditary angioedema (HAE) is a rare autosomal dominant disorder characterized by recurrent episodes of non-pitting, asymmetric swelling affecting the skin, mucous membranes, and potentially life-threatening laryngeal edema. The condition results from deficiency or dysfunction of C1 esterase inhibitor, leading to uncontrolled activation of the complement and contact systems.
HAE is caused by mutations in the SERPING1 gene encoding C1 esterase inhibitor, with Type I showing reduced levels and Type II showing dysfunctional protein. Deficient C1 inhibitor activity leads to excessive bradykinin production through uncontrolled kallikrein activation, resulting in increased vascular permeability and the characteristic angioedema without urticaria.
Diagnosis should be suspected in patients with recurrent angioedema without urticaria, especially with family history, abdominal pain episodes, or laryngeal involvement. Laboratory confirmation requires measuring C1 inhibitor levels and function, along with C4 levels which are typically low during attacks and between episodes in most patients.