First of all, I am not a doctor, nor do I work in the medical field, but I can tell you what WebMD says. It says that emphysema occurs when the lungs are damaged, specifically the air sac lining. The number one cause of this is smoking, although WebMD does state that they do not know why these are so interlinked. The site also states that people born with an AAT deficiency are more apt to get this disease, because AAT, or Alpha-1 antitrypsin, is a protein that circulates in the blood and it keeps white blood cells from damaging normal cells. Some people do not produce enough of this, leading to emphysema as well as liver problems, because it does not protect these organs as it should.
Although AAT deficiency and smoking are the primary causes, scientists believe that second-hand smoke and air pollution may also be damaging the lining of the air sacs and causing emphysema.