Identifying Types of HAE

HAE is caused by a problem in a person’s genetic code for a single protein, known as C1-INH.

As you may remember from high school biology, each person receives 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 the abnormal, disease-causing gene from both parents. Biologists call these autosomal (AW toe ZOAM ul) recessive genes. The parents of the affected child have the gene, but not the disease. The parents are considered carriers of the disease.

This is not the case in HAE. In HAE, just one problem gene will cause the disease. Biologists call this an "autosomal dominant" gene.

FACT : If you have HAE, there is a 50-50 chance that your child will also have HAE.

Rarely, HAE can occur in a person without a previous family history of HAE. This is due to a spontaneous change in the gene of the sperm or egg that formed the developing person. Not only will this person have the disease, but also the potential to pass this gene (and the disease) to their children. Because each person with HAE has either an affected gene or an unaffected gene to pass to the next generation, each child will have a 50-50 chance of also having the affected gene and the disease.

There are three main types of hereditary angioedema (HAE):

• Type I: Overall levels of C1-INH are low in type I HAE, and this is the most common type of HAE. About 85% of people with HAE have type I HAE. It is equally common among men and women.
• Type II: In type II HAE, the C1-INH levels are normal, but the existing C1-INH does not function properly. This is the second-most common type of HAE, and about 15% of people with HAE have type II HAE. It is equally common among men and women.
• Type III: In type III HAE, C1-INH lab tests are normal, but the person has symptoms of HAE. This is an extremely rare type of HAE, and it is not entirely understood. Most people with type III HAE are women.