Alpha-1 Antitrypsin Deficiency, also called Alpha-1-Proteinase Inhibitor (API) deficiency, is a genetic disorder characterized by the production of an abnormal amount of AAT protein and reduced circulating levels of this protein. Subjects with AAT deficiency are at increased risk for developing Emphysema. It is believed that this is the result of the chronic activity of elastase released by cells continually present in the lungs in low numbers.