AAT deficiency is a genetic condition caused by a lack of AAT. In healthy individuals, the lungs contain a natural enzyme called neutrophil elastase that, under normal circumstances, helps the lungs by digesting damaged, aging cells and bacteria. This process promotes healing of the lung tissue. Unfortunately these enzymes don't know when to stop, and eventually attack the lung tissue instead of helping it heal. That's where AAT comes in. By destroying the enzyme before it can cause actual damage to healthy lung tissue, the lungs proceed to function normally. When there is not enough AAT, however, the lung tissue will continue to be destroyed, which may lead to the chronic lung disease, emphysema.