C1 esterase inhibitor (angioedema)

General Information

C1 esterase inhibitor (C1-INH) is a highly glycated polymorphic protein (protein) that belongs to the family of serine proteases, or serpins. The polypeptide chain contains 478 amino acids and the molecular weight is 105 kilodaltons.

C1 esterase inhibitor is an inactivator of activated coagulation factor 12. It also inhibits plasmin, coagulation factor 11 and kallikrein. It is also an inhibitor of complement components – C1r and C1s.

On the other hand, C1-INH is an acute phase reactant protein, its production is stimulated by interleukin-6, interleukin-6, interferon-α and interferon-γ.

C1-INH deficiency increases the permeability of the blood vessel wall and causes angioedema (swelling around the blood vessel). This condition may be congenital or acquired.

Hereditary angioedema is an autosomal dominant disorder. There are 2 forms of the disease: in variant I, the synthesis of C1 inhibitor is reduced, and in variant II, an abnormal form of C1 inhibitor is synthesized, due to which its activity decreases.

Symptoms

From a clinical point of view, there is no difference between these two forms. The disease begins in childhood or adolescence - with subcutaneous and/or submucous edema. The swollen area is painless, non-swelling, non-compressible (that is, it does not disappear under pressure). Episodes are self-limiting - that is, the swelling will go away by itself in 2-5 days. The frequency, severity, and intensity of its development are variable. The causes have not been fully studied.

The usual location of edema development is: face, limbs, genitals, respiratory and gastrointestinal tract. Vomiting and diarrhea are symptomatic when localized in the intestines. When the center of swelling is located in the respiratory tract, a life-threatening obstruction (suffocation of the respiratory tract) may develop. Treatment of angioedema involves long-term administration of mild androgens, which increase serum C1-INH concentrations in both forms of the disease.

An acquired form of angioedema has been described, especially in elderly patients with lymphoproliferative, autoimmune, neoplastic diseases.

Other forms of angioedema

• Allergic angioedema (histamine-induced)
• Pseudoallergic angioedema (induced by cyclooxygenase inhibitors)
• Caused by converting enzyme inhibitors (eg: arterial hypertension in patients treated with drugs that increase serum bradykinin concentration;
• Idiopathic angioedema – such angioedema is sometimes accompanied by urticaria.

Preparation of the patient: The study is conducted on an empty stomach

Reference norms: 210 – 390 mg/l

Interpretation of results

A low level of C1 esterase inhibitor is found in congenital angioedema type I. However, 15% of patients with congenital angioedema have elevated protein levels. The rate is also low in acquired angioedema.

The normal level of C1 esterase inhibitor in children up to 6 months is different from that of adults.