(… deh-FIH-shun-see) An inherited condition in which the body either does not make enough of a protein called alpha-1 antitrypsin (AAT) or makes an abnormal form of AAT. AAT is made in the liver and helps protect the body’s organs, especially the liver and lungs, from damage. AAT deficiency can lead to serious lung conditions (including emphysema and bronchiectasis) and liver conditions (including cirrhosis, hepatitis, and liver cancer). It may also cause inflammation of the blood vessels and a rare skin condition that causes painful lumps on or under the skin. Lung problems caused by AAT deficiency almost always occur in adults, but liver and skin problems may occur in both adults and children. AAT deficiency is caused by a mutation (change) in a gene called SERPINA1. Also called alpha-1 antitrypsin deficiency.