Alpha-1 antitrypsin (ān'tē-trĭp'sĭn) deficiency (AATD) is a common, serious disease that is passed down from parents to children. It can cause liver and lung disease. The liver makes a protein called alpha-1 antitrypsin that goes into the bloodstream. This protein protects the lungs and allows them to work normally. If there is not enough alpha-1 antitrypsin, it is called alpha-1 antitrypsin deficiency (AATD).

Alpha-1 antitrypsin deficiency is the most common genetic cause of liver disease in children. It is the most common genetic disease that leads to liver transplant in children.