Studies estimate that about 50 percent of smokers will develop COPD. So it's obvious that some who smoke develop lung disease, but not all. It remains a mystery why this is. Most researchers speculate the answer has something to do with genetics.
The human body is composed of 37.2 trillion cells. Every cell has a nucleus, inside of which is a DNA molecule packaged in threadlike structures called chromosomes. DNA molecules consist of genes, which act as recipes for creating proteins. Each protein carries out some bodily function.
Most genes are the same in all people, although about one percent are unique, making every person unique. Unique genes are the result of gene mutations. Often these mutations are hereditary, and are handed down from parents. This might explain why some diseases, like asthma, are hereditary.
Other mutations are acquired during a person's lifetime. This might occur when a DNA molecule copies itself during cell division. This might also occur as a result of environmental exposure, such as to chemicals in cigarette smoke.
As far as the impact of genetics on COPD is concerned, very little is known. Here is some of what is known.
- Alpha-1-Antitrypsin. This is a protein produced by the liver that prevents the natural breakdown of lung tissue. Mutations in the SERPINA1 gene cause Alpha-1-Antitrypsin Deficiency. This results in the early development of emphysema even in those not exposed to cigarette smoke or other environmental triggers. This is the only specific genetic mutation known to cause COPD. It is hereditary. But this only explains 1-2 percent of COPD cases.
- Basal Cells. These are cells lining air passages that play a crucial role in producing other cells responsible for keeping the lungs healthy. They also replace lung cells that are injured or die. Researchers have discovered 676 genes in basal cells that were either over or under expressed in smokers. Four of these cells may be responsible for the early development of lung disease. One theory suggests that smoking causes them to reprogram basal cells to act abnormally. These changes are going on even in smokers who otherwise appear to be healthy.
- Inflammatory Response. Smoking may trigger some genes to initiate an immune response where inflammatory cells are recruited to the lungs. These inflammatory cells treat certain chemicals from cigarette smoke as an enemy, resulting in chronically inflamed airways, or bronchitis. Inflammation may also be responsible for the breakdown of lung tissue, or emphysema.
- Airway Remodeling. Some gene mutations may be responsible for airway remodeling, or airway changes, such as a thickening of the airway walls leading to permanent airway obstruction or narrowing.
- Lung Development. Hedgehog Interacting Protein is a protein that researchers think plays a role in lung development. They suspect it is produced on chromosome 7, and a COPD gene in this area may result in abnormal lung development, resulting in airflow obstruction. Researchers are keying in on various other locations where specific genes might be located that play a role in lung development.
- Asthma Genes. Another thing to consider is that researchers have discovered over 100 different genes responsible for asthma. It's also possible that some of these genes, especially when exposed to chemicals from cigarette smoke, might also cause COPD. So some people might have a genetic code making them susceptible to both diseases.
- Heterogeneous. Every case of COPD is unique. This might be because the combination of COPD genes, or gene mutations, is unique in each person. This might explain why some COPD patients start to lose lung function earlier and faster than others. It might explain why COPD triggers vary from one patient to the next. It might also explain why each patient benefits from different medicine combinations.
Once the genes responsible for lung disease are discovered, researchers can focus on them to create treatment options to block their effects. Ideally, this will help those with COPD live better with it, and prevent our children from developing lung disease in the future.