A person with hereditary angioedema has a rare, inherited illness that causes episodes of sudden swelling of the hands, feet, face, intestines, throat and air passageways.

Severe attacks of hereditary angioedema can be life-threatening, but most episodes of swelling resolve.

The cause of hereditary angioedema is an abnormal gene that results in low levels of C1 inhibitor protein. C1 inhibitor protein prevents episodes of inflammation in the body. When levels of the protein are low, inflammation occurs much more easily in all tissues of the body.