Men may have higher rates of bowel cancer because of a female genetic fault, research suggests.
Scientists identified an alteration on the female X chromosome, one of the packages of DNA that determine gender, associated with bowel cancer.
The fault appears to be involved in the development of cancer in both men and women. But it may have a bigger effect in men, say the researchers.
The defective X chromosome region is linked to reduced activity of a gene called SHROOM2 that controls how cells develop and take shape.
Women have two X chromosomes, so if one has the fault the other normally functioning version may mask it.
But this would not apply to men, who have just one X chromosome paired with a male Y chromosome.
Professor Richard Houlston, one of the scientists from from the Institute of Cancer Research in London, said: "To our knowledge, this is the first time that anyone has shown that one of the sex chromosomes is involved in the development of a cancer that can afflict both sexes. This may help explain why bowel cancer is slightly more common in men. Ultimately, it could also help us target screening to those who are more at risk of the disease."
The study, reported in the journal Nature Genetics, also uncovered two other genetic risk variants for bowel cancer, bringing the known total to 20.
The scientists analysed data from five international studies looking for single letter changes in the genetic code (single nucleotide polymorphisms, or SNPs) linked to bowel cancer.
A second variant identified was in a gene called CDKN1A which governs a number of tumour suppressing biological pathways.
The third affected a gene called POLD3 which influences two pathways that repair DNA damage.
Bowel cancer is the third most common cancer in the UK affecting 41,000 men and women each year.
Dr Lesley Walker, from the charity Cancer Research UK which funded the study, said: "This research shows how a range of genes could be behaving in bowel cancer, potentially leading to new treatments for the disease."
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