Hereditary Angioedema Types I and II

**Semantic type:** Disease or Syndrome

**Definition:** Autosomal dominant inherited disorders characterized by abnormalities of C1 inhibitor. Patients present with swelling of the skin, subcutaneous tissues, and mucosa sites. In type I hereditary angioedema, the plasma levels of C1 inhibitor are decreased. In type II hereditary angioedema, the C1 inhibitor is dysfunctional and its plasma levels may be normal or elevated.