Some people have a genetic variation that makes them more susceptible to chronic obstructive pulmonary disease (COPD) if they smoke tobacco, according to new research from Wake Forest University School of Medicine and colleagues.
"The genetic variant we studied seemed harmless on its own," said Alireza Sadeghnejad, M.D., Ph.D., lead author. "But when someone has this variant, there is more of an adverse effect of smoking on lung function. Therefore, in combination with smoking, this genetic variant represents a risk factor for COPD."
Emphysema and chronic bronchitis are components of COPD, which is the fourth leading cause of death in the U.S. and the only top-10 killer that is increasing in frequency. The World Health Organization predicts that by 2020, COPD will be the third-leading cause of death worldwide.
The study is published online and will appear in a future print issue of the American Journal of Respiratory and Critical Care Medicine. The researchers studied two variations (-1112C and -1112T) of the interleukin-13 (IL-13) gene. The gene is responsible for the production of the IL-13 protein that is involved in pulmonary inflammation and susceptibility to COPD.
Everyone has two copies of the gene, one inherited from each parent. The investigation suggests that having two copies of -1112T in the IL-13 gene is linked with a more profound adverse effect of cigarette smoking on lung function.
Study participants were 1,073 men at least 40 years old who had smoked 20 or more pack-years. One pack-year is equivalent to smoking one pack a day for a year. Participants underwent genetic testing and a pulmonary function test known as Forced Expiratory Volume, which is the volume of air that can be forced out in one second after taking a deep breath.
Jill Ohar, M.D., senior researcher and a professor of internal medicine-pulmonary, said it's likely that -1112C/T is one of several genetic variants that influence the risk of a smoker developing COPD. About 25 percent of smokers develop the disease, suggesting that genetic factors, in addition to environmental exposure (in this case cigarette smoking), play a role.
"This finding may help us to understand why some smokers develop COPD and improve our understanding of how the disease develops," said Ohar. "It shows us that it's likely the gene/environment interaction sets you up for this disease."
Sadeghnejad said that by understanding more about the role of IL-13 in COPD, the protein may one day be a target for new drugs for the disease.
The variant has been shown to be associated with asthma, which may help explain why COPD and asthma tend to cluster in families, Ohar said.
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