Down's gene boost fights cancers

People with Down's syndrome are less likely to get some cancers - and scientists hope to exploit this to help other people at risk. Most cases of Down's happen because the baby is carrying an extra chromosome packed with genetic information.

But Johns Hopkins University experts, writing in the journal Nature, say the additional copy of one gene might help block cancers. But another scientist said boosting the gene might actually help cancer spread.

Up to 95% of Down's syndrome cases are caused by "trisomy 21", in which the baby has three, rather than two, copies of chromosome 21, and the hundreds of genes it contains. Common features of the condition include facial differences, learning difficulties, congenital heart defects and a far higher risk of childhood leukaemia.

However, advances in medical science mean that the life expectancy of people with Down's has risen sharply, and now averages 60 years. This increase led to some studies finding that adults with Down's syndrome appear to have less chance of developing certain cancers which involved "solid" tumours.

The Johns Hopkins researchers used experiments in mice to try to find out which part, if any, the extra chromosome might be responsible for this. When mice designed to develop intestinal cancers were bred with mice which had a third copy of a chromosome, they developed far fewer cancers.

The team pinpointed a single gene, Ets2, and found that the chance of developing tumours seemed to be related to the number of copies of the gene carried by each mouse. They believe that it might be possible to come up with a treatment which could help prevent tumours in humans. "The phenomenon might be exploited to identify a pharmacological-based approach to tumour protection," they wrote in the journal.

However, David Threadgill, an Associate Professor of Genetics at the University of Carolina at Chapel Hill, sounded a warning note. In an accompanying article, he said that there was some evidence that Ets2 could actually boost the spread, or metastasis, of cancer around the body, making it far harder to treat. He wrote: "Individuals with Down's syndrome are at a lower risk of developing solid tumours, probably owing to the high Ets2 levels in their epithelial cells - but they might be at a greater risk of cancer metastasis."

A spokesman for Cancer Research UK said: "The relationship between Down's syndrome and cancer is complex. People with this genetic disorder have higher risk of leukaemia, but seem to have lower risk of some other cancers. The study suggests that a gene which offers protection against the development of certain tumours may increase the risk of cancer spread. More research is needed to unravel this paradox if this discovery is to benefit cancer patients in the future."