Alpha-1 antitrypsin deficiency is caused by mutations in the SERPINA1 gene on the q arm of chromosome 14. This gene encodes an enzyme called alpha-1 antitrypsin. Which expressed in the liver and released into the blood to protect the lungs from the attack of another enzyme called neutrophil elastase. Neutrophil elastase is made by white blood cells in response to infection or irritants to digest damaged tissue in the lungs.
When SERPINA1 gene is mutated, the abnormal alpha-1 antitrypsin protein gets stuck in the liver and is unable to pass into the bloodstream. Lungs are left vulnerable to attack by neutrophil elastase without the protection of this protein. So the accumulation of alpha-1 antitrypsin damage the liver and lungs both.