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What Is Alpha-1 Antitrypsin Deficiency?

Alpha-1 antitrypsin (an-tee-TRIP-sin) deficiency, or AAT deficiency, is a condition that raises your risk for lung disease (especially if you smoke) and other diseases.

Some people who have severe AAT deficiency develop emphysema (em-fi-SE-ma)—often when they're only in their forties or fifties. Emphysema is a serious lung disease in which damage to the airways makes it hard to breathe.

A small number of people who have AAT deficiency develop cirrhosis (sir-RO-sis) and other serious liver diseases.

Cirrhosis is a disease in which the liver becomes scarred. The scarring prevents the organ from working well. In people who have AAT deficiency, cirrhosis and other liver diseases usually occur in infancy and early childhood.

A very small number of people who have AAT deficiency have a rare skin disease called necrotizing panniculitis (pa-NIK-yu-LI-tis). This disease can cause painful lumps under or on the surface of the skin.

This article focuses on AAT deficiency as it relates to lung disease.


Alpha-1 antitrypsin, also called AAT, is a protein made in the liver. Normally, the protein travels through the bloodstream. It helps protect the body's organs from the harmful effects of other proteins. The lungs are one of the main organs that the AAT protein protects.

AAT deficiency occurs if the AAT proteins made in the liver aren't the right shape. They get stuck inside liver cells and can't get into the bloodstream.

As a result, not enough AAT proteins travel to the lungs to protect them. This increases the risk of lung disease. Also, because too many AAT proteins are stuck in the liver, liver disease can develop.

Severe AAT deficiency occurs if blood levels of the AAT protein fall below the lowest amount needed to protect the lungs.

AAT deficiency is an inherited condition. "Inherited" means it's passed from parents to children through genes.

Doctors don't know how many people have AAT deficiency. Many people who have the condition may not know they have it. Estimates of how many people have AAT deficiency range from about 1 in every 1,600 people to about 1 in every 5,000 people.


People who have AAT deficiency may not have serious complications, and they may live close to a normal lifespan.

Among people with AAT deficiency who have a related lung or liver disease, about 3 percent die each year.

Smoking is the leading risk factor for life-threatening lung disease if you have AAT deficiency. Smoking or exposure to tobacco smoke increases the risk of earlier lung-related symptoms and lung damage. If you have severe AAT deficiency, smoking can shorten your life by as much as 20 years.

AAT deficiency has no cure, but treatments are available. Treatments often are based on the type of disease you develop.

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Last Updated: October 11, 2011