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."
Carl Froch knocks out Lucian Bute during their IBF World Super Middleweight Title bout at Nottingham Capital FM Arena on May 26, 2012 in Nottingham, England. (Photo by Scott Heavey/Getty Images)
A man trying to catch a young wild stallion in Duelmen, Germany, Saturday, May 26, 2012. It is believed that this is the last herd of wild horses on the European continent in this 350 hectare reservation in western Germany, where more than 300 of the indigenous horses stay free and wild without any care under the protection of the Duke of Croy. Only once a year the new born stallions are caught and sold, all mares stay with the herd and guarantee the survive of the endangered species. (AP Photo/Martin Meissner)
Miami Marlins center fielder Chris Coghlan stretches for a triple hit by San Francisco Giants' Ryan Theriot in the eighth inning of a baseball game in Miami, Saturday, May 26, 2012. The Marlins defeated the Giants 5-3. (AP Photo/Lynne Sladky)
An animal rights activist dressed as a cat protests the Ringling Brothers Circus outside the circus venue before the start of a show in Mexico City, Saturday, May 26, 2012. (AP Photo/Marco Ugarte)
A resident watches from atop a building as fire fighters, unseen, spray water after a fire broke out at a garment factory, left, in Gandhi Nagar area of New Delhi, India, Sunday, May 27, 2012. No casualty has been reported so far and the reason for the fire is not known. (AP Photo/Manish Swarup)
A fisheye view with a wide-angle lens shows center court Philippe Chatrier as Jo-Wilfried Tsonga of France and Andrey Kuznetsov of Russia play their first round match at the French Open tennis tournament in Roland Garros stadium in Paris, Sunday May 27, 2012. (AP Photo/Michel Spingler)
Will Power (12), of Australia, drives under Mike Conway, of England, after they made contact in the first turn during IndyCar's Indianapolis 500 auto race at Indianapolis Motor Speedway in Indianapolis, Sunday, May 27, 2012. (AP Photo/Tom Hemmer)
The Phoenix fireboat sprays plumes of water as part of the Golden Gate Bridge's 75th anniversary celebration on Sunday, May 27, 2012, in San Francisco. The commemoration included a vintage boat parade and a fireworks display slated for the evening. (AP Photo/Noah Berger)
Jessica Ennis of Great Britain competes in the Women's High Jump in the women's heptathlon during the Hypomeeting Gotzis 2012 at the Mosle Stadiom on May 26, 2012 in Gotzis, Austria. (Photo by Ian Walton/Getty Images)