Hereditary angioedema

Hereditary angioedema (HAE) is a rare genetic condition causing recurrent episodes of severe swelling, most often affecting the skin, abdomen, or airway, due to a deficiency or dysfunction of a protein called C1-inhibitor. Attacks are not caused by allergies and do not respond to standard allergy treatments like antihistamines or adrenaline. It requires specific management with specialist immunology or allergy input.

It is caused by inherited mutations affecting the gene for C1-inhibitor, a protein that normally regulates certain inflammatory pathways in the body. Without adequate functioning C1-inhibitor, these pathways become overactive, leading to fluid leakage from blood vessels and swelling. It is inherited in an autosomal dominant pattern, meaning each child of an affected parent has a 50% chance of inheriting the condition.

Symptoms include recurrent episodes of swelling affecting the skin (face, limbs, or genitals), severe abdominal pain from swelling within the gut wall, and, most seriously, swelling of the throat or tongue that can obstruct breathing. Attacks typically build up over hours and can last several days if untreated. Unlike allergic swelling, HAE attacks are not usually accompanied by hives or itching.

Yes, airway-involving attacks are potentially life-threatening medical emergencies, which is why everyone with HAE should have on-demand emergency treatment readily available and a clear action plan. Abdominal attacks, while not usually life-threatening, can be extremely painful and are sometimes mistaken for other causes of abdominal pain, occasionally leading to unnecessary surgery if HAE is not recognised. With appropriate treatment, including preventive medication for some patients, most attacks, including severe ones, can be managed successfully.

Diagnosis is confirmed through specific blood tests measuring C1-inhibitor levels and function, alongside a relevant clinical history of recurrent swelling episodes, often with a family history of similar symptoms. Genetic testing can further confirm the diagnosis in some cases. Because HAE is rare and its symptoms can overlap with other causes of swelling, diagnosis is sometimes delayed, so specialist referral is valuable when it is suspected.

Treatment includes on-demand medications, such as C1-inhibitor concentrate or icatibant, used to treat attacks as they start, and long-term preventive medication for people with frequent or severe attacks. Standard allergy treatments, including antihistamines, adrenaline, and steroids, are not effective for HAE, which is an important distinction from allergic angioedema. A specialist immunology or allergy team, ideally at a centre experienced with HAE, coordinates ongoing management.

There is currently no cure for the underlying genetic condition, but modern on-demand and preventive treatments have transformed the ability to control symptoms, with many people now living full, active lives with infrequent, well-managed attacks. Ongoing specialist follow-up helps optimise treatment over time as new therapies continue to become available. Research into more advanced and convenient treatment options continues to progress.

Hereditary angioedema is caused by a genetic C1-inhibitor deficiency and does not respond to antihistamines, adrenaline, or steroids, the standard treatments for allergic reactions. Allergic angioedema is typically triggered by a specific allergen, often accompanied by hives or itching, and does respond well to standard allergy treatments. Because the correct emergency treatment differs so significantly between the two, anyone with confirmed HAE should carry information (such as a medical alert card) explaining this to any emergency responders.

Anyone with a confirmed HAE diagnosis should have ongoing specialist immunology or allergy follow-up as standard care, with an individualised action plan for managing attacks. If HAE is newly suspected, based on recurrent unexplained swelling, particularly with a family history, a private allergy and immunology referral can typically be arranged within about one to two weeks. Seek emergency care immediately for any swelling affecting the throat or causing breathing difficulty, regardless of whether the diagnosis has yet been formally confirmed.