Which are the causes of Hereditary Angioedema?

Hereditary Angioedema (HAE) is a rare genetic disorder characterized by recurrent episodes of swelling in various parts of the body. It is caused by a deficiency or dysfunction of a protein called C1 esterase inhibitor (C1-INH), which plays a crucial role in regulating the immune system and preventing excessive inflammation.

1. Genetic Mutation: The primary cause of HAE is a genetic mutation that affects the production or function of C1-INH. This mutation is usually inherited from one or both parents who carry the defective gene. HAE follows an autosomal dominant pattern, meaning that an affected individual has a 50% chance of passing the mutation to their children.

2. C1-INH Deficiency: In most cases of HAE, the underlying cause is a deficiency of functional C1-INH. This deficiency leads to uncontrolled activation of certain proteins in the complement system, a part of the immune system responsible for eliminating foreign substances and pathogens. Without sufficient C1-INH, these proteins become overactive, resulting in increased vascular permeability and the characteristic swelling seen in HAE.

3. C1-INH Dysfunction: In some rare cases, individuals with HAE may have normal levels of C1-INH, but the protein is dysfunctional. This means that although it is present in sufficient quantities, it fails to perform its regulatory function effectively. The dysfunctional C1-INH is unable to control the complement system, leading to recurrent episodes of angioedema.

4. Types of HAE: There are three main types of HAE, each with a distinct genetic cause. Type I HAE is the most common form and is characterized by low levels of functional C1-INH. It is caused by mutations in the SERPING1 gene, which provides instructions for producing C1-INH. Type II HAE is characterized by normal or elevated levels of dysfunctional C1-INH and is caused by mutations in the SERPING1 gene. Type III HAE, also known as estrogen-dependent HAE, primarily affects women and is associated with mutations in the F12 gene, which encodes a protein involved in blood clotting.

5. Triggers: While HAE is a genetic disorder, certain triggers can precipitate episodes of angioedema. These triggers vary among individuals but commonly include physical trauma, emotional stress, hormonal changes (such as menstruation or pregnancy), infections, certain medications, and even unknown factors. It is important for individuals with HAE to identify their specific triggers and take appropriate precautions to minimize the risk of swelling episodes.

6. Diagnosis: Diagnosing HAE involves a combination of clinical evaluation, medical history assessment, and laboratory tests. Genetic testing can confirm the presence of specific mutations associated with HAE. Additionally, measuring C1-INH levels and assessing complement system activity can aid in the diagnosis.

7. Treatment: Although there is no cure for HAE, various treatment options are available to manage the symptoms and prevent or reduce the frequency and severity of angioedema episodes. These include on-demand therapies to treat acute attacks, such as C1-INH replacement therapy, bradykinin receptor antagonists, and plasma-derived therapies. Prophylactic therapies can also be used to prevent attacks in individuals with frequent or severe episodes. These may include long-term C1-INH replacement therapy, androgen therapy, or other medications that help regulate the complement system.

8. Lifestyle Management: In addition to medical interventions, individuals with HAE can benefit from lifestyle modifications to reduce the risk of triggering angioedema episodes. This may involve stress reduction techniques, avoiding known triggers, maintaining a healthy diet, staying hydrated, and having a comprehensive emergency plan in place.

Conclusion: Hereditary Angioedema is a genetic disorder caused by a deficiency or dysfunction of C1 esterase inhibitor (C1-INH). Genetic mutations, primarily inherited from parents, lead to low levels or dysfunctional C1-INH, resulting in uncontrolled activation of the complement system and recurrent episodes of angioedema. Identifying triggers and implementing appropriate treatment and lifestyle management strategies are crucial for individuals with HAE to minimize the impact of this rare condition on their daily lives.