It's the genes that put some smokers at increased risk of developing chronic obstructive pulmonary disease (COPD) in later life, according to a study.
COPD is characterized by progressive decline in lung function, and encompasses chronic bronchitis and emphysema.
Around 90 percent of COPD is caused by long-term cigarette smoking, yet only 25 percent of chronic tobacco smokers go on to develop it.
For the study, US-based researchers Alireza Sadeghnejad, Jill Ohar, Eugene Bleecker and colleagues from the Wake Forest School of Medicine and Saint Louis University looked at a disintegrin and metalloprotease (ADAM) gene known as ADAM33 in 880 long-term heavy smokers.
ADAM33 is located on chromosome 20, and has been linked to asthma in previous studies.
The new study is unique in comparing long-term smokers with COPD versus a control group of long-term smokers without COPD.
And researchers found five single nucleotide polymorphisms (SNPs) - human DNA sequence variations - in ADAM33 that were more frequent in the COPD group than in the group of smokers without COPD. One SNP, known as S1, had a particularly strong link to lung abnormalities.
"Functional studies will be needed to evaluate the biologic significance of these polymorphisms in the pathogenesis of COPD," said the authors.
The study has been published in BioMed Central's open access journal Respiratory Research.