When three genes are better than two

For years, scientists have been wondering why people with Down's Syndrome are less likely to get cancer than the rest of us. Now researchers writing in the journal Nature say they've found the answer.

People with Down's have three copies of chromosome 21 instead of the usual two. This extra chromosome causes the disorder but, the scientists discovered, it also contains a gene that stops the growth of tumours.

The scientists identified the gene in question, known as Dscr1, by studying mice that have extra copies of many of the genes on chromosome 21. Humans normally only have two copies of Dscr1, but it turns out that an extra copy suppresses cancer by stopping tumours from growing blood vessels.

The discovery could lead to potential new treatments, say cancer experts.