Genetics play a role in the development of COPD.  It is more common among relatives of those with COPD who smoke than unrelated smokers.  Currently, the only clearly inherited risk factor is alpha 1-antitrypsin deficiency (AAT).  This risk is particularly high if someone deficient in alpha 1-antitrypsin also smokes.  It is responsible for about 1–5% of cases   and the condition is present in about three to four in 10,000 people.  Other genetic factors are being investigated,  of which many are likely.