SERPINA1 and alpha 1-antitrypsin deficiency: Alpha-1 antitrypsin deficiency (AATD) is a rare genetic condition characterized by low plasmatic levels of the protein alpha-1 antitrypsin (AAT), a protease inhibitor synthesized and secreted mainly by hepatocytes whose main function is to protect the lungs from proteolytic damage caused by proteolytic enzymes such as neutrophil elastase (NE) or proteinase-3.