Genome-wide search points to new bowel cancer gene

Two studies, published in the current issue of the journal Nature Genetics, reported the discovery of a genetic element which researchers say increases bowel cancer risk by 20 per cent. The researchers, from London and Edinburgh, estimate that one in two people in the general population are carriers of the genetic element, making it the first common genetic link to bowel cancer.

There are three different genes already known to contribute to bowel cancer risk - those that trigger familial adenomatous polyposis (FAP), hereditary non-polyposis colorectal cancer (HNPCC) and MYH associated polyposis (MAP) - however these are rare and only account for one in ten cases of the disease, according to the charity CancerBackup.

Much of the variation in inherited risk of bowel cancer is probably due to combinations of common low risk variants, write the researchers. Although the genetic element does not confer a high enough risk to warrant a genetic test, it is 'an important first step', said Professor Ian Tomlinson of Cancer Research UK, who co-lead the London arm of the study. However 'we still have a long way to go before we have a complete picture of all the genes involved', he added.

In the hunt for the gene, the two teams of researchers together scanned the entire genome of more than 30,000 people in total. However, before scanning large groups of people, they first narrowed down their search by tagging all the single DNA 'letter' changes that occurred more frequently in a smaller group, half of which had bowel cancer. They then scaled up the study, repeating the tagging process many times in larger groups of patients and healthy people, to see which regions were most strongly linked to bowel cancer. The studies showed that a particular region on chromosome 8, also thought to increase risk of prostate cancer in men, contained a gene which raised bowel cancer risk by 20 per cent and is associated with one in ten bowel cancers.

'We are now using an even more refined 'genome wide scan' to discover yet more genes linked to bowel cancer', reports Professor Malcom Dunlop, from the University of Edinburgh and the Medical Research Council's Human Genetics Unit, who led the Edinburgh arm of the study.

Eventually it may be possible to develop a genetic test which looks at different combinations of low-risk genes, raising the prospect of begin able to identify those at risk from bowel cancer who may benefit from regular screening. 'In future we hope studies like this across a range of cancers will help people at increased risk of developing the disease through the development of tailored screening and treatment programmes', said Harpal Kumar, Chief Executive of the study's funder, Cancer Research UK.