Learn About Alpha-1 Antitrypsin Deficiency | American Lung Association

Learn About Alpha-1 Antitrypsin Deficiency

Alpha-1 antitrypsin (AAT) deficiency is a rare genetic disorder that is passed on in families and affects the lungs, liver and skin. When this condition affects the lungs, it causes emphysema, a part of COPD (chronic obstructive pulmonary disease) along with chronic bronchitis.

Key Facts

  • Alpha-1-antitrypsin (AAT) is a protein that keeps an enzyme called elastase, produced by white blood cells to fight infection in check.
  • In alpha-1 antitrypsin deficiency, AAT levels are reduced, allowing elastase enzymes to increase. This results in the destruction of lung tissue and the development of emphysema.
  • AAT deficiency is inherited. Severe disease is more likely to occur in people who receive an abnormal gene from both parents.
  • People with AAT deficiency may have a normal lifespan, although those who smoke cigarettes have a faster decline in lung function and develop earlier lung disease.

What Is AAT Deficiency?

AAT deficiency is a genetic disorder in which the body's ability to produce a protein called alpha-1 antitrypsin (AAT) is reduced, resulting in damage to the lungs and other organs.

How AAT Deficiency Affects Your Body

When AAT levels are reduced or absent, the balance between AAT and elastase is thrown off.  This means that elastase can cause damage. Normally, this enzyme plays an important role in fighting infection, but too much of it can harm healthy tissue. It causes damage to the lining and alveoli of the lung, resulting in emphysema, or permanent enlargement of the lung's airways. This can cause problems with exchange of gas and clearance of mucus from the lung. Additionally, AAT deficiency can affect the liver, leading to poor function and increasing the risk of cirrhosis and liver cancer. In the first three decades of life, liver disease is more common than lung disease. In some individuals, AAT deficiency may cause frequent red, painful nodules on the skin.

How Serious Is AAT Deficiency?

There are different severity levels of AAT deficiency. This depends on the type of gene alteration that is inherited from each parent. The normal gene from each parent is called an M. The gene alteration that is most abnormal is Z. A patient that inherits a Z from each parent is the most at risk for disease as compared to those that receive an abnormal gene from only one parent. Those with severe deficiency are at higher risk of life-threatening complications such as liver failure and lung damage, and may require a liver or lung transplant in the late stages of disease. Individuals with AAT deficiency who smoke or are exposed to environmental pollutants are at increased risk for developing lung disease. However, non-smoking individuals with AAT especially with a less severe gene alteration can have a more normal life span.


    This content was developed in partnership with the CHEST Foundation, the philanthropic arm of the American College of Chest Physicians.


    Approved by Scientific and Medical Editorial Review Panel. Last reviewed August 4, 2016.

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