The disease is characterized by recurrent attacks of angioedema of the skin and mucous membranes and can be life threatening at the engagement of the airways. Hereditary angioedema (HAE) is caused by hereditary C1-INH deficiency in the heterozygous base. A large number of different mutations of the gene of C1-INH have been described. The disease is characterized by recurrent attacks of angioedema of the skin and mucous membranes and can be life threatening at if effecting the airways. In the most common form, HAE type I, the concentration C1-INH is low in serum. HAE type II is due to various point mutations formed a dysfunctional protein. Functional analysis of C1-INH are required for establishing the diagnosis. C1-INH concentrations at HAE type II is usually normal, but in a variant, very high values can be seen when the dysfunctional protein forms a complex with albumin. C4 levels in HAE is routinely low, even between attacks.
Acquired C1-INH deficiency, due to hyper catabolism of C1-INH, is often associated with the presence of M-components and one should suspect lympho proliferative disease. The characteristic of acquired C1-INH deficiency in patients with M-component is that the levels of C1q and C1s are usually very low. In another group of patients with acquired C1-INH deficiency one has seen autoantibodies against C1-INH.
Another group of patients with angioedema, and / or urticaria can be identified with this diagnosis. Patients with hypocomplementemic urticarial vasculitis syndrome (Hood's) you find low C1q levels, normal levels of C1-INH and C1s, and low levels of C4 and C3. These patients have autoantibodies against the collagen-like portion of C1q.