C1-inhibitor (C1inh) is a serine protease inhibitor (serpin) protein, the main function of which is inhibition of the complement system. It circulates in blood at levels of around 0.25-0.45 g/l.

C1inh is the largest member of the serpin class of proteins (G1). It is probably the highest glycosylated protein. Remarkably, it has O-glycosylated residues, which is uncommon for proteins that are not secreted into the skin or gut.

The gene is located on the eleventh chromosome (11q11-q13.1).

Deficiency of this protein is associated with hereditary angioedema (or angioneurotic edema), which is marked swelling of the face, mouth and airway that occurs spontaneously or to minimal triggers. In 85% of the cases, the levels of C1inh are low, while in 15% the protein circulates in normal amounts but it is dysfunctional. In addition to the episodes of facial swelling and/or abdominal pain, it also predisposes to autoimmune diseases, most markedly lupus erythematosus, due to its consumptive effect on complement factors 3 and 4.

External links

• OMIM 606860 (http://www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=606860)