Other Down's syndrome News
Down's gene may prevent cancer
The chromosomal abnormality that affects people with Down's syndrome also guards against cancer.
Down's sufferers have three instead of two copies of chromosome 21, one of the long coiled strands of DNA and associated proteins that carry the genes.
Some studies have suggested that having this abnormality, called a trisomy, may lessen the risk of cancer. However, the findings have not been conclusive.
New research provides clear evidence that a chromosome 21 trisomy can be protective. It could also lead to new forms of cancer treatment, researchers believe.
US scientists led by Dr Roger Reeves at Johns Hopkins University in Baltimore, Maryland, tested the idea out in mice genetically engineered to have the equivalent of Down's and human colon cancer.
They found a gene on chromosome 21 called Ets2 which appeared to prevent mice developing cancer.
The protective effect could be explained by having three copies of the gene - one on each chromosome - instead of two.
Having more copies of a gene increases the "dose" of the protein that gene produces. Three copies of Ets2 might protect against cancer developing while two does not.
The findings, published in the journal Nature, came as a surprise, because Ets2 is generally thought to encourage the growth of tumours.
The discovery could be exploited to promote cancer resistance, say the authors.