If you or your child has hereditary angioedema (HAE), you may have heard that C1 inhibitor deficiency plays a role in many HAE attacks. A C1 inhibitor (C1INH) deficiency can lead to sudden swelling episodes that may be life-threatening without immediate treatment.

If your specialist diagnosed you with C1INH deficiency, you may have questions about what it means. This guide explains what C1INH is, how a deficiency affects HAE, and why it can lead to swelling attacks.

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Effects of a C1INH Deficiency

When your body doesn’t have enough C1INH or can’t use C1INH properly, inflammation and swelling can happen in different parts of your body. This sudden, uncontrolled swelling is called angioedema.

Not all types of angioedema come from a C1INH deficiency, but the most common types of HAE do.

Why HAE Attacks Happen

An HAE attack is a swelling episode that tends to happen regularly in people with HAE. If you don’t make enough C1INH or your C1INH doesn’t function as it should, your body can make too much bradykinin, a chemical that makes blood vessels leak fluid. Too much bradykinin can lead to swelling during an HAE attack.

An HAE attack can happen in response to a trigger that increases bradykinin. However, in many cases, HAE attacks happen spontaneously, without an obvious trigger.

These attacks aren’t allergic, although they can sometimes look like an allergic reaction, such as tongue or throat swelling. Common allergy medications, including antihistamines, epinephrine, and corticosteroids, won’t work to treat them.

Common Triggers for HAE Attacks

Around 40 percent of HAE attacks happen in response to identifiable triggers, while the other 60 percent happen with unknown triggers. If you or your child has had HAE for a while, you may begin to recognize the triggers that are most likely to cause attacks.

Triggers can include:

• Strong emotions, like stress and anxiety
• Hormone fluctuations, especially involving estrogen
• Infections, including the common cold and flu
• Physical trauma, including injuries, surgery, or dental procedures
• Pressure on tissues from typing or other repetitive actions
• Certain medications, including ACE inhibitors and estrogen birth control

Triggers of HAE attacks can’t always be identified. If you can identify your triggers, you can take steps to avoid them and lower your risk of future HAE attacks.

What C1INH Deficiency Means for HAE Types

Not all types of HAE are the same. How much C1INH you have and how your C1INH functions help determine which type of HAE you have.

• Type 1 HAE — Your body doesn’t produce enough C1INH. This means there isn’t enough C1INH in your body to help prevent uncontrolled inflammation and swelling. In type 1 HAE, a genetic mutation (change) affects the body’s ability to make enough C1INH.
• Type 2 HAE — Your body may produce normal levels of C1INH, but the C1INH doesn’t function properly. As a result, it can’t regulate inflammation and swelling as it should.
• HAE with normal C1INH — This rare type of HAE doesn’t involve C1INH deficiency or C1INH dysfunction. If you or your child has this rare type, your C1INH levels and function are normal. HAE attacks in this type are likely related to other proteins involved in inflammation that are affected by genetic mutations.

C1INH Testing and HAE Diagnosis

Blood tests that check C1INH can help doctors diagnose HAE types 1 and 2. Your doctor or your child’s doctor may also order C4 tests or genetic tests. After asking about symptoms and doing a physical exam, they may recommend the following C1INH tests.

• C1 inhibitor quantitative test — A C1INH quantitative test measures how much C1INH is in your blood. If you have HAE type 1, a quantitative C1INH test will show that you have low levels of C1INH.
• C1 inhibitor functional test — Doctors also perform C1INH functional tests while diagnosing HAE. These tests can show whether your C1INH is working properly.

If you have type 2 HAE, your quantitative test may come back normal, or you may even have excessive C1INH in your blood sample. However, your functional test results indicate low function of C1INH. People with HAE type 1 also typically have test results that indicate low C1INH function.

Exploring Treatments for C1INH Deficiency

Once your doctor has performed C1INH tests and better understands your HAE, they can use your test results to guide treatment decisions. Based on what your HAE specialist learns about your C1INH levels and function, they may recommend treatments, including plasma-derived C1 inhibitors or recombinant C1 inhibitors.

On-Demand Treatments

Some treatments for HAE related to a C1INH deficiency are on-demand treatments. These treatments should be used right away when you notice signs of swelling. Some on-demand treatments rapidly replace C1INH to help control swelling in the same way natural C1INH does.

Prophylactic Treatments

Preventive treatments can be used as long-term prophylaxis or short-term prophylaxis if you’re going to encounter an HAE trigger, such as an upcoming dental procedure. Long-term prophylaxis usually means taking medicine regularly to help prevent HAE attacks before they happen.

Just like on-demand treatments, prophylactic treatments sometimes include C1INH to make up for your body’s low levels of functional C1INH.

An Emergency Action Plan

Your HAE specialist will likely advise you to have an emergency action plan in place for unexpected HAE attacks related to C1INH deficiency or dysfunction. While many HAE attacks cause swelling in the face, hands, or feet, some cases can involve swelling around the throat or airway.

Throat or tongue swelling can block the airway and prevent breathing. This is a medical emergency and can be life-threatening without immediate action. Be prepared to use on-demand medications as soon as you notice signs of an attack, and get emergency medical care right away for trouble breathing, trouble swallowing, or swelling of the tongue or throat.

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On myHAEteam, people share their experiences with hereditary angioedema, get advice, and find support from others who understand.

Does your HAE involve a C1 inhibitor deficiency? Let others know in the comments below.