Genetics of Alpha-1

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View About Chromosome 14 Animation

Alpha-1 antitrypsin (AAT) deficiency is an inherited disorder, which means it is caused by abnormal genes that can be passed from parents to children.

AAT deficiency results when there is a mutation in the gene that directs the body to make the AAT protein. This gene is located on chromosome 14. Chromosome 14 is not a "sex chromosome," meaning that both males and females have it and can pass it on.

There are many variations or alleles of the AAT gene, but the most common are:

• M – Normal (associated with normal amounts of AAT protein)
• S and Z – Abnormal (associated with deficient amounts of AAT protein)
• Null – Abnormal (deficient; no AAT protein is detected)

Every person has two copies of the AAT gene – one from each parent. It is the combination of genes that an individual receives from the parents that determines whether he or she is "normal," has AAT deficiency, or is a carrier of AAT deficiency.

These diagrams show how AAT deficiency can be passed from one generation to another.

View Genetics of AAT Deficiency Animation

It is important to understand that the disorder can be passed along either by someone who has AAT deficiency or by someone who is a carrier. It is also important to understand that any one of the parents’ children could have any one of the four gene combinations.

It is estimated that worldwide there are 3.4 million people with deficiency allele combinations (ZZ, SZ, SS) and 116 million who are carriers (MS, MZ).¹