The team, led by Professor Magnus Svartengren from the Karolinska Institute, has been looking at the interaction of the environment with the genes of nearly 45,000 twins over 40 years old. They were interested in twins with chronic bronchitis or emphysema.
Speaking at a meeting of the Biochemical Society held in Loughborough on March 5th, 2009) he said, "We know that only a subset of smokers get chronic lung disease" (chronic obstructive pulmonary disease - COPD), "yet non-smokers also get COPD, so there must be genetic factors involved."
Smoking is the main risk factor for COPD which includes bronchitis and emphysema. "We found that heritability accounts for 40% of chronic bronchitis, yet only 14% of those genetic influences are linked to smoking," he said. Not all smokers develop COPD, yet people who have never smoked can also develop COPD. Smokers who develop COPD seem to be genetically more susceptible to the harmful effects of cigarette smoke than smokers who do not develop COPD.
COPD which progressively and irreversibly damages lungs is one of the most challenging diseases in the world, both in terms of treatment and prevention. Currently it is one of the global top five causes of mortality and is predicted to rise. It is also closely associated with other major causes of death such as heart disease.
Of the 45,000 Swedish twins first investigated, 392 twins were tested for lung function. All the twins answered a series of questions about their smoking habits and respiratory symptoms with emphasis on whether a twin was likely to have a lung disease. Those selected for lung function tests had blood and urine samples analysed to identify markers of inflammation that could be linked to problems with other organs, such as heart disease. "Our results show a complex relationship between COPD and inflammation elsewhere in the body. Inflammation could explain the high prevalence of heart and other diseases in patients with COPD," said Professor Svartengren.
"We found sex differences in the impact of genetic factors on lung function. Our preliminary findings also suggest genes play an important role in the development of emphysema. Women seem to be more predisposed to suffer the harmful respiratory consequences of tobacco smoking," said Professor Svartengren.
The reasons why people smoke are complex. Behaviour that leads people to smoke is governed by genetic and environmental factors. However, the genes that influence behaviour are different to the genes that make some people, women in particular, more vulnerable to COPD. "Our twin studies suggest that genetic factors are of importance in individual differences in lung function," said Professor Svartengren.
Professor Svartengren and his team will now carry out further analyses to evaluate factors that explain how the disease discriminates between men and women.
(1) It's an old joke about the somewhat silly politically correct tone of the major old media publications; when God declares he is going to end the world, the joke goes, the Washington Post headline is "World to End Tomorrow, Women and Children Most Affected" while the New York Times top headline is "World to End Today, Minorities Hardest Hit." Joke not guaranteed to be funny to actual NY Times or Washington Post readers, who really do think they are more educated and compassionate than everyone else.