Hereditary angioedema is an autosomal dominant condition in which a decrease in either the amount of C1 inhibitor or the function of C1 inhibitor results in swelling when the body is exposed to certain substances.
Attacks may be preceded by a painful macular rash. The swelling may be life-threatening. The image below from wiki commons (uploaded by Dr Heilman) shows a child with hereditary angioedema.
Increased levels of bradykinin play a central role in the pathphysiology and therefore ACE inhibitors (which prevent bradykinin breakdown) can cause angioedema.
Treatment acutely is with IV C1 inhibitor concentration.
The anabolic steroid danozol may be given prophylactically as it increases liver C1 inhibitor production by an unknown mechanism.