Hereditary angioedema (HAE) is an inherited condition that causes swelling in the tissue in various parts of the body. Attacks can target a single hand or foot, or may appear in a portion of the face. Swelling in the abdomen can cause severe pain and is often misdiagnosed as appendicitis and could result in unnecessary surgical procedures. Swelling in the throat can prevent breathing and is a life-threatening condition.
HAE is hereditary because most cases are inherited from a family member, although it is possible to develop HAE as a result of a genetic mutation without having the disease in your family. People with HAE have a genetic change in a gene that causes low levels or malfunctioning copies of a protein known as C1 inhibitor or C1-INH. C1 inhibitor works in the blood to regulate levels of the chemical bradykinin. If there is too much bradykinin, cells in blood vessels will contract and pull together. This leaves gaps between the cells that make up the blood vessel where fluid from the blood (known as serum) can leak out of the blood and into the surrounding tissue which causes swelling.
There are three basic types of HAE:
• Type I – Patients have very low levels of C1-INH. When levels drop below a critical value, fluid can leak out of blood vessels and cause swelling. Approximately 85 percent of patients have HAE Type I.
• Type II – Patients have normal levels of C1-INH, but the protein is not normal and does not function properly.
• Type III – This type of HAE is not fully understood, but seems to be associated with estrogen levels and is often associated with pregnancy or the use of oral contraceptives containing hormones.
Hereditary angioedema symptoms can appear at different ages. Approximately half of patients report symptoms before the age of 7. Over two-thirds report having HAE attacks by the time they were 13.
Attacks may occur more often during puberty and adolescence. Other events that can trigger an HAE attack include:
• Menstruation – some women are more likely to have an attack during their periods
• Trauma to the body including medical or dental procedures