Hereditary Angioedema (HAE) is a rare genetic disorder caused by a deficiency or dysfunction of a protein called C1-inhibitor. This defect leads to the overproduction of a substance known as bradykinin, which increases the permeability of blood vessels, causing fluid to leak into surrounding tissues and resulting in swelling (edema).

HAE is inherited in an autosomal dominant pattern, meaning that each child of an affected parent has a 50% chance of inheriting the condition. However, there are also cases caused by new mutations, with no prior family history. In Greece, more than 55 families with over 200 diagnosed patients have been identified, including approximately 20–30 children.

HAE is characterized by recurrent episodes of non-inflammatory swelling in different parts of the body, including the skin and subcutaneous tissue (such as the face, hands, or feet), the gastrointestinal tract (causing severe abdominal pain, vomiting, and diarrhea), and the upper respiratory tract (such as the larynx, tongue, or throat), which can be life-threatening due to airway obstruction. These episodes occur without itching or rash, do not respond to standard treatments like antihistamines or corticosteroids and typically last 2 to 5 days. Although the age of symptom onset varies, most patients will experience their first episode during childhood or adolescence.