SERPINA1 and Alpha-1-antitrypsin deficiency: Alpha-1 antitrypsin deficiency (AATD) is a clinically under-recognized autosomal, codominant, genetic disorder characterized by decreased serum levels and/or functionality of alpha-1 antitrypsin (AAT), which is a 152-kDa glycoprotein that represents the major inhibitor of the human neutrophil elastase.