SERPINA1 and chronic obstructive pulmonary disease: α-1 antitrypsin (AAT) is secreted by the liver, and if the mutant allele is present, the protein aggregates in hepatocytes causing liver fibrosis, cirrhosis, and cancer and the reduction in circulating AAT also results in emphysema and Chronic Obstructive Pulmonary Disease (COPD) in the lungs.