Alpha-1 antitrypsin is a serine protease inhibitor. Its main substrate is neutrophil elastase. Its function in the lung is to protect to pulmonary tissue from degradation by neutrophil elastase. A deficiency of AAT results in early onset emphysema and chronic obstructive pulmonary disease, and liver disease. Pulmonary symptoms usually present in the fourth and fifth decade of life. Hepatic injury can occur at any age, include neonates.
|The gene that encodes AAT is highly polymorphic. The AAT protein variants are usually prefixed with Pi (proteinase inhibitor). Many AAT variants result in normal AAT expression and function. The most common non-deficiency allele is PiM. Other AAT variants result in AAT deficiency. The most common AAT deficiency alleles code for the PiS and PiZ protein variants. Patients with the PiMM (homozygous) phenotype have NORMAL AAT expression and function.
Patients who are PiSS and PiZZ (homozygous) or are heterozygous for deficiency alleles (eg PiSZ) have DEFICIENT AAT expression (low AAT concentration).
Patients who have only one AAT deficiency gene (heterozygotes eg PiMZ, PiMS) do not have the disease, but they are "carriers" of the deficiency. Their AAT levels are usually lower than normal, but this does not cause a serious risk of health problems.
Over 100 alleles for AAT have been identified, The AAT protein variants listed above are the most common.
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|AAT concentration should be determined before AAT phenotyping is requested. AAT phenotyping will be automatically requested by the laboratory when a low AAT concentration is detected.
|Ref. Range Notes
|Pi Varient reported
|IP Acute TAT
|IP Routine TAT
|GP Acute TAT
|GP Routine TAT