Alpha-1 antitrypsin is a naturally occurring enzyme that protects your lungs from damage. Some people are born with a gene variant that results in a deficiency of alpha-1 antitrypsin. There are no symptoms of this deficiency, but if you have the gene, you can develop chronic obstructive pulmonary disease (COPD) more easily and at a younger age than those with adequate amounts of alpha-1 antitrypsin.
Smoking is particularly dangerous for those with alpha-1 antitrypsin deficiency; if you smoke and develop COPD at an early age (before age 45), your doctor may test you for the gene. However, because the condition is rare, not everyone is tested for an alpha-1 antitrypsin deficiency.