People with familial emphysema have a hereditary deficiency of a blood component, alpha-l-protease inhibitor, also called alpha-l-antitrypsin (AAT).
The elastase-AAT imbalance is thought to be a result of the effects of smoking, rather than inherited as in familial emphysema. Some evidence for this theory comes from studies on the effect of tobacco smoke on lung cells.
Because familial emphysema results from a deficiency of AAT in affected individuals, efforts to minimize the risk of emphysema have been directed at increasing the circulating AAT levels either by promoting or increasing the production of AAT within the individual, or augmenting it from the outside.