C1 inhibitor deficiency: hereditary and acquired forms.

C1 inhibitor deficiency can be hereditary or acquired. The hereditary disorder has two types, each of which is inherited as a dominant disorder, with genetic mechanisms leading either to low levels of normal C1 INH and little or no mutant problem as a result of mRNA or protein synthetic defects or degradative mechanisms (Type I) or with point mutations and synthesis of a functionless protein product with transinhibition of the normal allele (Type II). The acquired disorder with low C1q is due to C1 INH consumption associated with lymphoma or connective tissue disease (Type I) and/or autoimmune mechanisms (Type II). The swelling of all types is due to absence of inhibition of the plasma kinin forming cascade with liberation of bradykinin while complement activation, a critical marker of the disorder, is not responsible for the swelling. Treatment employs androgenic compounds, antifibrinolytic agents, or replacement therapy.