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 C1-INH (called “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) attacks in different parts of the body. 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. Find out more about HAE.

Q: Are there different types of HAE?

A: There are 2 major types of HAE. Type I is caused by low levels of C1-INH protein. Type II is caused by a decreased function of some of the C1-INH protein. An additional, very rare type of HAE has also been identified. Formerly known as type III, it is now designated as “HAE with normal C1 inhibitor.” The defect is now thought to be a defect in coagulation Factor XII, rather than the C1-INH. 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 inheritance patterns with HAE.

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

A: If you have HAE and your parenting partner does not, each of your children has a 50-50 chance of inheriting 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.

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 clues that help physicians identify 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: How common is HAE?

A: According to the US Hereditary Angioedema Association, the prevalence of HAE is estimated to be around 1 in 10,000 to 50,000. 9 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; it is almost always low in people with either type. 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 function level. No single test can diagnose HAE with normal C1-INH.