It is long known that smoking is responsible for respiratory diseases like chronic bronchitis. However, Swedish researchers have discovered that genes also play a major role in the development of the disease.
The team of researchers, led by Jenny Hallberg, of the Department of Public Health Sciences at Karolinska Institutet in Stockholm, studied more than 40,000 Swedish twins for finding out to what extent does behaviour, environment and genes each play a role in the development of chronic bronchitis.
'Smoking behavior has a known genetic component and smoking is a primary risk factor for chronic bronchitis,' Hallberg said.
It was found that around 40 percent of the risk for chronic bronchitis was due to hereditability, and at the same time, 14 percent of the genetic risk was also linked to a genetic inclination to smoke, irrespective of whether the individual actually smoked or not. The researchers also discovered that chronic bronchitis in addition to emphysema, account for the majority of the cases of chronic obstructive pulmonary disease, or COPD.
For the study, the researchers assessed data from the Screening Across Lifespan Twin (SALT) study in Sweden, which surveyed all known living twins in Sweden born in 1958 or earlier.
In the survey, the researchers asked questions on zygosity, whether the twins shared 100 or 50 percent of their genetic material, smoking history and a checklist of common diseases. The questions were designed in order to find out whether the interviewee had chronic bronchitis or not.
The survey data and statistical modelling was used to differentiate the genetic and environmental influences, responsible for an individual's risk of developing chronic bronchitis: genetic factors, shared environmental factors (i.e., experienced by both twins) and non-shared environmental factors.
'[This] study on the population-based Swedish Twin Registry, showing a genetic effect for the development of chronic bronchitis that does not differ by sex is the first to our knowledge to quantify heritability of the disease,' said Hallberg.
The results of the study pointed to a number of intriguing possibilities as chronic bronchitis had earlier been reported to be more prevalent in women than men.
'It is possible that women are more prone to report symptoms. Or, more likely, this could be an effect of smoking being more harmful for women due to their smaller lungs from start (exposure to cigarette smoke relative to body size),' she said.
However, she warned at the same time that the finding that the genetic factors that contribute to chronic bronchitis were largely independent of factors responsible for smoking, should not be interpreted to mean that smoking has no effect on chronic bronchitis.
'Although there was some genetic interplay, it is safe to say that smoking itself, and not the genes that predispose one to smoking, is a larger risk factor in developing chronic bronchitis of environmental exposures—- primarily smoking—- than genetic predisposition. This is true of both men and women,' said Hallberg.
The research was published in the first issue for March of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.