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Hereditary Angioedema (HAE)
What is it?
Hereditary Angioedema (HAE) is a rare inherited disease that causes significant swelling (often referred to as edema) in the tissues of the body, like the abdomen or face. Depending on the severity of the disease, some people will have many attacks each month, while others can go years without a swelling attack. Minor trauma or stress may trigger an attack but swelling often occurs without a known trigger. HAE can affect the gastrointestinal system and can cause severe abdominal pain, nausea, and vomiting. This disease can also affect the airway and can restrict breathing leading to life-threatening obstruction of the airway if an intervention does not occur.
What causes it?
HAE patients have a defect in the gene that controls a blood protein known as the C1 Inhibitor. The genetic defect results in the production of either inadequate or a dysfunctional C1-Inhibitor protein. Normal C1-Inhibitor helps to regulate the interactions between certain blood vessels that assist in disease fighting, inflammation, and coagulation. Because a defective C1-Inhibitor protein cannot function correctly, a biochemical imbalance can occur which results in a production of unwanted proteins that cause small blood vessels called capillaries to release fluids into surrounding tissue, thereby causing edema.
What Causes an Attack?
Most attacks occur with no apparent reason. However, anxiety, stress, minor trauma, surgery, and illnesses like a cold or flu can be triggers. Dental procedures or any trauma to the oral cavity can make HAE patients susceptible to airway attacks. The following have been shown to increase the risk of an attack:
- Anxiety or stress
- Trauma
- Surgery
- Respiratory Illnesses
- Menstruation
- Pregnancy
- Certain medications: specifically, ACE Inhibitors (a medication used for high blood pressure) and oral contraceptives
Who does it affect?
Hereditary Angioedema is called hereditary because the genetic defect is passed down through families. The defect is autosomal dominant. This means that if a parent has HAE then their child has a 50% chance of inheriting the disease. However, the absence of the disease in the family does not completely rule out the HAE diagnosis since some cases occur as a result of a spontaneous mutation of the C1-inhibitor gene. These patients can then pass the improper functioning gene down to their children.
What are the symptoms?
Symptoms of hereditary angioedema typically begin in childhood and worsen during puberty. On average, untreated individuals have an attack every 1 to 2 weeks, and most episodes last for about 3 to 4 days. The frequency and duration of attacks vary among people with hereditary angioedema, even among people in the same family.
- Throat swelling
- Sudden hoarseness
- Repeat episodes of abdominal cramping without obvious cause
- Diarrhea
- Vomiting
- Swelling in the arms, legs, lips, eyes, tongue, or throat
- There absence of itching or hives.
How is it diagnosed?
The diagnosis of HAE is confirmed by a blood test or genetic test. There are two specific tests, C1-inhibitor quantitative and C1-inhibitor functional, that confirm HAE. Other lab tests including a C4 level can identify the presence of HAE during an attack. C4 levels should be elevated during an attack, decreased immediately following an attack, and normal in between attacks. There are three main types of HAE that can be determined based on genetic and laboratory studies. They are as follows:
- Type I: In type I HAE, the C1-INH level is low but functional. About 85% of people with HAE have type I, thus making it the most common type.
- Type II: In type II HAE, the C1-INH levels are normal, but they do not function properly. About 15% of people with HAE have type II.
- Type III: In type III HAE, all C1-INH lab tests are normal, but the person still has symptoms of HAE. This is an extremely rare type, and is not entirely understood. This type is found primarily in women.
How is it treated?
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