Questions About Understanding Hereditary Angioedema

Q: What is hereditary angioedema (HAE)?

A: People suffering from HAE have a low level of an important protein in their blood. The protein is called C1-INH (pronounced “C1 inhibitor,” which is short for “complement 1 esterase inhibitor”). C1-INH regulates and "turns off" various reactions in the body. In people with HAE, a low level or decreased function of C1-INH is thought to be the major reason for recurrent, often severe, and even life-threatening swelling (angioedema) in different parts of the body. Find out more about HAE.

Q: Are there different types of HAE?

A: There are two major types of HAE. Type I is caused by low levels of C1-INH. Type II is caused by a decreased function of some of the C1-INH protein. Recently, another kind of HAE (type III) has been identified. In these patients, C1-INH levels are usually normal. Learn more about types of HAE.

Q: How serious is HAE?

A: The severity of HAE is determined by the frequency, location, and degree of swelling. Swelling in the throat may compromise the airway. Therefore, these attacks of HAE can be life-threatening. Swelling in the intestines may cause severe abdominal pain and discomfort. Although the majority of the attacks are not life-threatening, they can seriously affect quality of life. Find out more about living with HAE.

Q: How does a person get HAE?

A: HAE is usually inherited. The abnormality in the C1-INH gene is passed down from a parent to a child. However, about 25% to 30% of HAE cases are caused by a new mutation. In these cases, there is no previous history of HAE in the family. If someone with HAE marries a person without the condition, there is a 50% chance their child will have HAE. Learn about what causes HAE.

Q: What causes hereditary angioedema (HAE)?

A: HAE is a rare genetic disease believed to be caused by an abnormality in a gene that makes C1-INH. C1-INH is short for complement 1 esterase inhibitor, a protein that helps regulate the immune system. Without this protein, people with HAE experience attacks of fluid retention and swelling. Learn about what causes HAE.

Depending on the severity of the disease, some people will have many attacks each month, while others could go months or even years without a swelling attack.

Q: What are the symptoms of HAE?

A: HAE may mimic other types of medical conditions, such as allergic reactions or appendicitis. However, there are some clues that help physicians identify HAE and distinguish it from other medical problems. The ABCs of HAE and eight simple questions can help you and your physician differentiate HAE from other medical problems.

Q: Since HAE is hereditary, will I pass HAE to my children?

A: If you have HAE and your spouse does not, each of your children has a 50-50 chance of inheriting HAE. Learn about what causes HAE.

Q: How common is HAE?

A: HAE is quite rare. Only about 1 in 30,000 to 50,000 people has HAE. Find out more about HAE.

Q: How is HAE diagnosed?

A: HAE is diagnosed by taking a blood sample and measuring the level of C1-INH in the blood. C4 (another important blood protein) is often used in screening tests. Type I HAE is diagnosed by confirming a low level of C1-INH. People with type II HAE will have a normal C1-INH level, but an abnormal C1-INH functional level. No single test can diagnose type III HAE.