Angioedema is a reaction marked by episodes of severe swelling of the skin. The swelling mostly occurs on the face and limbs, but also may be found in the intestinal tract and airways.

Angioedema may have several causes, including allergies, reactions to medications, and genetic factors.

Studies have found that angioedema often is linked to low levels of a protein called C1-inhibitor in the blood. This protein controls the levels of another protein called C1, which is a part of the immune system and plays a role in the inflammatory response.

There are different types of angioedema based on the underlying causes and the levels of C1 inhibitor (C1-INH) in the blood. 

Acute allergic angioedema

Acute allergic angioedema is the most common type of angioedema that occurs as a consequence of an allergic reaction. In this type of angioedema, the body mistakenly identifies certain harmless external substances, such as food or medications, as harmful. It then releases certain chemicals to attack these external substances. These chemical reactions in the body lead to angioedema and cause the skin to swell.

Non-allergic angioedema

Non-allergic angioedema is caused by a reaction to medications such as angiotensin-converting enzyme (ACE) inhibitors. The onset of this type may vary from days to months after first taking the medication.

Idiopathic angioedema

Idiopathic angioedema is the name given to angioedema of an unknown cause. This type is often chronic, relapsing, and mostly accompanied by hives or urticaria

Hereditary angioedema (HAE)

Hereditary angioedema is inherited and occurs due to genetic abnormalities that cause a deficiency in the levels of C1 protein. Hereditary angioedema can be further divided into three types:

HAE type 1

This is one of the most common types of hereditary angioedema. It is seen in approximately 80-85 percent of cases diagnosed with hereditary angioedema. The levels of C1 inhibitor in patients with this type are considerably below normal levels. This is due to a mutation in SERPING1 gene that encodes for the C1 inhibitor. A large number of people diagnosed with type 1 hereditary angioedema are known to have a family history of the disease. However, this type of angioedema also can occur as a result of spontaneous mutations.

HAE type 2  

This type of angioedema is seen in 15-20 percent of cases. It also occurs as a result of mutations in the SERPING1 gene, but in this case the mutations cause the C1-inhibitor protein to malfunction.

HAE type 3 

Hereditary angioedema of this type is very rare. It is caused by mutations in the gene responsible for the production of a protein called coagulation factor 12. The mutations cause the production of overactive coagulation factor 12. This, in turn, leads to higher production of bradykinin, a compound that promotes inflammation. Although predominant in women, this type of hereditary angioedema also affects men.

Acquired angioedema

Acquired angioedema is caused by antibodies destroying C1-inhibitor, leading to disease development. 

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