Alpha-1 antitrypsin (AAT) is a liver-produced protein blocker that circulates in the blood, protecting lung tissue from damage due to inflammation. Mutations in the AAT gene can lead to defective AAT production, causing its accumulation in the liver and significantly lowering its levels in the blood. This increases the risk of pulmonary emphysema and liver cirrhosis. AAT deficiency (AATD) affects about 1 in 6,000 Caucasians in North America, although only 5% of cases are diagnosed. It is the second most common genetic lung disease after cystic fibrosis.