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What Causes Alpha-1 Antitrypsin Deficiency?

Alpha-1 antitrypsin (AAT) deficiency is an inherited disease. "Inherited" means it's passed from parents to children through genes.

Children who have AAT deficiency inherit two faulty AAT genes, one from each parent. These genes tell cells in the body how to make AAT proteins.

In AAT deficiency, the AAT proteins made in the liver aren't the right shape. Thus, they get stuck in the liver cells. The proteins can't get to the organs in the body that they protect, such as the lungs. Without the AAT proteins protecting the organs, diseases can develop.

The most common faulty gene that can cause AAT deficiency is called PiZ. If you inherit two PiZ genes (one from each parent), you'll have AAT deficiency.

If you inherit a PiZ gene from one parent and a normal AAT gene from the other parent, you won't have AAT deficiency. However, you might pass the PiZ gene to your children.

Even if you inherit two faulty AAT genes, you may not have any related complications. You may never even realize that you have AAT deficiency.

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Alpha-1 Antitrypsin Deficiency Clinical Trials

Clinical trials are research studies that explore whether a medical strategy, treatment, or device is safe and effective for humans. To find clinical trials that are currently underway for Alpha-1 Antitrypsin Deficiency, visit

October 11, 2011 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.