Hereditary angioedema (Q39703)

Hereditary angioedema is caused in the majority of cases by genetically determined low absolute (type I) or functional (type II) levels of C1 inhibitor, a plasma proteinase inhibitor involved in regulation of complement activation. It is characterised clinically by recurrent subcutaneous and/or submucosal oedema and can result in life-threatening laryngeal obstruction. Involvement of the digestive tract commonly causes abdominal pain. This and the absence of accompanying urticarial weals or itch distinguish it from the common form of angioedema, which is part of the spectrum of urticaria.