Alpha-1 antitrypsin (AAT) deficiency is an inherited disorder that can cause disease in the lung and liver. Symptoms include inability to breathe, recurring respiratory infections and fatigue as well as liver cirrhosis, leaving patients at risk for development hepatocellular carcinoma. AAT deficiency is caused by mutations in SERPINA1, the gene that encodes the AAT protein, a serine protease inhibitor or serpin. The AAT protein is made in the liver and plays a crucial role in protecting lung function.