Hereditary Angioedema

Hereditary Angioedema (HAE) is a rare, potentially life-threatening and debilitating disease that can cause recurrent and unpredictable attacks of swelling in various parts of the body, including the stomach, hands, feet, arms, legs, genitals, throat, and face. These attacks can be painful and disabling. The number of attacks widely varies within those affected, from virtually never to multiple times a month.

In its Type I and II forms, HAE is an autosomal dominant disease, meaning that to be affected a person needs to have only have one copy of an abnormal gene. HAE can be inherited from either parent, but in some cases, it can be caused by a spontaneous gene change in the person. In the case of HAE Type I, the defective gene causes people to have missing or abnormally low levels of a protein called C1 esterase inhibitor (C1-INH). In HAE Type II, the C1-INH levels are sufficient but the protein does not function properly. The lack of functional C1-INH leads to unregulated production of bradykinin, which results in attacks.

Diagnosing HAE requires a clinical evaluation where a doctor can review the person’s history, and family history, of symptoms, do a physical exam, and conduct diagnostic blood tests. Due to the disease rarity, HAE is often misdiagnosed as a histamine-mediated reaction, but this condition does not respond to being treated with antihistamines or corticosteroids since the swelling is caused by overproduction of bradykinin.

Since HAE can cause swelling of the throat, this condition can be life-threatening. But treatment options are available to prevent attacks and help people manage the disease.

Hereditary Angioedema is classified into three types based on what problem the genetic defect causes.

HAE Type I - Low levels of C1-INH in the body; this is the most common form of HAE; this accounts for ~85% of people with HAE
HAE Type II - Normal levels of C1-INH, but it does not function normally; this accounts for ~15% of people with HAE.
HAE normal C1-INH - Normal levels of C1-INH and it functions normally; this is extremely rare and not well understood and this accounts for <1% of people with HAE.