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Medical Definition of A1-trypsin inhibitor
1. A glycoprotein that is the major protease inhibitor of human serum, is synthesised in the liver, and is genetically polymorphic due to the presence of over 20 alleles; individuals appropriately homozygous are deficient in a1-trypsin and are predisposed to pulmonary emphysema and juvenile hepatic cirrhosis because of alterations in the amino acid and sialic acid components of the glycoprotein. A1-Antitrypsin also inhibits thrombin. Synonym: a1-trypsin inhibitor, human a1-proteinase inhibitor. (05 Mar 2000)