Down's syndrome is the commonest inherited chromosome disorder and occurs in about 1 in 700 human births. A down's syndrome baby has 3 copies of chromosome 21 instead of the usual 2 copies.
Scientists working at John Hopkins University in the USA have bred mice that have 3 copies of the chromosome and displayed the hallmarks of Down's syndrome found in humans. The characteristics of Down's syndrome are face, brain and skull abnormalities and sufferers often have problems with their immune system, heart and muscles.
No one knows why the extra chromosome leads to the problems we see with Down's syndrome but the scientists at John Hopkins believe that the mice l reflect what goes on in humans and will help lead to an explanation of how the extra chromosomal material causes Down's syndrome.
