Posted on 04/02/2008 11:47:39 PM PDT by neverdem
Genetic mutation raises risk of colon cancer in Caucasians but not in Japanese.
Geneticists searching for genetic variants that raise the risk of colorectal cancer have found the first one to have an effect specific for a particular ethnic group. The mutation boosts the risk of colon cancer in Caucasians by 10%, but has no such effect in the Japanese population.
The gene variant is the first known to boost the risk of colon cancer, the world's third most common form of cancer, in one population group but not in another, says Malcolm Dunlop of the University of Edinburgh, UK, who led the study.
The discovery raises the possibility of race-specific tests to assess the risk of developing colorectal cancer, which is among the more easily treated cancers if the susceptibility is spotted early.
Cancer geneticists have looked for race-specific genes that boost the risk of other cancers. But results may be most relevant for colorectal cancer, since this is much more dependent than most other cancers on lifestyle factors. Other common cancers, such as breast cancer and prostate cancer, seem more unavoidable. "The good thing about bowel cancer is that it's preventable," says Dunlop.
Intriguingly, the genetic variant only has a race-specific effect on the risk of colon cancer. Both Caucasians and Japanese carrying this mutation had a roughly equal risk of developing rectal cancer, showing that the mutation's effects are likely to be both subtle and specific.
Genetic influence
Dunlop says that it is unclear how the mutation, found on chromosome 11, influences cancer risk. Indeed, he says, it is not even found within a gene, but rather in the mass of non-coding DNA.
The researchers discovered the mutation after taking DNA samples from more than 1,000 Scottish cancer patients, and from healthy controls. They sifted through more than half a million possible candidate gene variants to see which ones cropped up most often in patients compared to non-patients.
After repeating the process several times with many thousands more patients, and comparing the samples with those from other racial groups, they discovered three sites within the human genome that confer a definite risk of colorectal cancer — one of which had different effects on cancer risk depending on whether the patient was Scottish or Japanese.
It's unclear why this difference should exist, admits Dunlop, who reports his team's findings in Nature Genetics 1. Perhaps it could be due to other, unknown, genetic differences between different populations, or to differences in lifestyle factors such as diet.
Group of seven
Another similar study2, led by Richard Houlston of the Institute of Cancer Research in Sutton, UK, adds details of a further two gene variants linked to colorectal cancer, bringing the overall number to seven.
People with all seven of the known genetic risk factors are four to five times more likely than those with none to develop colorectal cancer, Dunlop says.
Britain has already begun a national testing programme for existing colorectal cancer. There may be significant public interest in a test that can spot people with risky genes before they ever develop the disease, Dunlop suggests, as it would allow people to tailor their lifestyles to try and avoid developing bowel cancer. "There will be a public debate about it," he predicts.
Race-specific, or even personalized, tests of cancer susceptibility are becoming a real possibility, Dunlop says — although he adds that such a prospect is "some time" in the future.
References Tenesa, A. et al. Nature Genet. doi:10.1038/ng.133 (2008). Tomlinson, I. P. M. et al . Nature Genet. doi:10.1038/ng.111 (2008).
Sounds like more results from genome wide association testing. Non-coding DNA used to be called junk DNA, and race was supposed to be an artificial, social construct.
did they consider dietary differences or are they just hypothesis shopping !
Diet probably has some role, but it doesn't explain why both groups had roughly equal risk for rectal cancer. For pathology, oncology and surgery, both cancers are frequently lumped together and called colorectal adenocarcinoma.
Dietary differences have already been explored and described at length. It’s likely that as time progresses we’ll increasingly find genetic links to cancer susceptibility just as we’ve found such links to any number of other diseases.
How can this be? My Marxist college professor assured me that race is just a social construct.
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