What Causes Hereditary Angioedema?

Researchers are still trying to determine the exact cause of hereditary angioedema (HAE), but much is known about the role played by complement 1 esterase inhibitor, or C1-INH. A defect in a person's genetic code for the C1-INH protein may be responsible for HAE. An abnormal code can lead to a deficiency in C1-INH (type I HAE) or an inability of existing C1-INH to function properly (type II HAE).

In order to understand how HAE is inherited, it is helpful to look at genetics. People receive half their genetic code from their mother and half from their father. In some diseases, such as cystic fibrosis or sickle-cell anemia, a child must receive one copy of the disease-causing gene from each parent. Biologists call these autosomal recessive genes. The parents of the affected child have the gene, but may not have the disease - these parents are considered carriers of the disease.

This is not the case in HAE. In HAE, just one defective gene will cause the disease. Biologists call this an autosomal dominant gene. This means that there is a 50-50 chance that a child who has one parent with HAE will also have HAE.

Children born without the abnormal gene will effectively prune the occurrence of HAE from that branch of the family tree. All successive generations (that child's children and grandchildren) will be free of HAE.

Rarely, HAE can occur in a person without a previous family history of HAE. This is due to a spontaneous change in the genetic code for the C1-INH protein. Not only will this person have the disease, but he or she will also have the potential to pass this changed gene (and the disease) to his or her children.

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FAQs about treating HAE

Questions about treating HAE? You’re not alone. Read the questions of other people learning how to treat HAE and see how they were answered. Find out more in Questions on Treating HAE.

Family tree

HAE can be caused by a problem in the genetic code for a single protein, so it can be inherited. Discover how it occurs in families, and how HAE may run in your family tree.