The finding offers fresh insights into the link between smoking and colorectal cancer.
The defect, alpha-1 antitrypsin deficiency, leaves people vulnerable to damage to the membranes - making both lungs and colon vulnerable, researchers reported in Molecular Genetics and Metabolism.
Researchers at the Mayo Clinic, Rochester, Minnesota, USA, studied 161 patients newly diagnosed with cancer, and compared them with 191 people of similar background.
They found that people who smoked and also had the deficiency faced a 20-times increased risk of developing colorectal cancer.
Alpha-1 antitrypsin deficient smokers have 20x increased risk of colon cancer
Overall, carriers of the deficient gene faced a 3.1 times increased risk of developing cancer. Smokers faced a 6.6 times increased risk.
Researcher Dr Ping Yang said, "This study provides important new insight into the controversy surrounding the link between cigarette smoking and colorectal cancer, confirming a strong association in a subgroup of colorectal cancers.
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