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Fewer tracheobronchial branches may be a genetically-related risk factor.
While chronic obstructive pulmonary disorder (COPD) is primarily caused by smoking and exposure to air pollution, some individuals are more likely to develop the progressive lung disease than others. Genetic variations in anatomy can affect the lungs’ ability to filter out noxious particulate matter.
The genetic variation concerns the number of branches in a person’s tracheobronchial tree. This system of branches, with smaller branches, known as bronchi, and even smaller branches, known as bronchioles, conducts air from the upper airways to the lungs. It’s called a “tree” because it looks like an upside-down tree with branches widening through the lungs.
The system is designed to filter out noxious particulate matter, such as air pollution or cigarette smoke before it gets to the lungs, but a decrease or increase in the number of branches can make some systems more efficient than others. While most people have up to 30,000 tiny bronchioles in each lung, a 2018 study by the National Academy of Sciences suggests individual variations can affect airflow.
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According to the study, variants are present in 26.5% of the general population. Some individuals may be missing a branch, while others may be born with an extra one. Those who have fewer branches may be at a higher risk of developing COPD later in life, because they start out with less than ideal lung function. This genetic variation in airway structure would not only explain why some non-smokers develop COPD but also why some lifelong smokers do not..
In terms of human survival, such variations might not have mattered as much before humans regularly smoked tobacco or were increasingly exposed to noxious pollution.
Since COPD is a progressive disease, it was previously thought to be the result of prolonged exposure to irritants which accelerated the normal decline of the lungs as a person aged. The knowledge that there is a genetic component has altered that perception. Evidence shows that the decline may be normal for adults who have this variation because they have lower lung function early in life.
Understanding the importance of such genetic variations can make it easier to predict who is likely to develop COPD and possibly develop personalized treatments. Confirming this genetic variation is not complicated or invasive, since variations can easily be measured by a CT scan. For patients with mild and moderate airflow limitation, early intervention may help prevent lung damage.