First Down Syndrome mouse created

By BBC News Online's Damian Carrington in Washington DC

Scientists have created a mouse with Down Syndrome (DS), and claim it is such an accurate model of the disorder that it has already revealed unknown features of the human version.

The researchers, speaking at the American Association for the Advancement of Science annual expo, also believe that the model will help reveal the key genes that affect the development of the face and skull.

This will shed light not just on DS but also other face and head deformities.

Mice have been inflicted with a wide range of human diseases, from Alzheimer's disease to cancer. These models help researchers understand the illnesses better and provide a test bed for potential therapies.

But until now, a good model of the genetic cause of mental retardation - DS - has eluded scientists.

Teams at Johns Hopkins University and the Jackson Laboratory in Bar Harbor, Maine, bred the mouse model to have not two but three copies of the entire chromosome region analogous to human chromosome 21. This duplication is what causes DS, which affects one baby in every 700.

'Absolute correspondence'

Using a laser-equipped, 3D-measuring microscope, the researchers compared the shape of the DS mice and "normal" mice. The DS mice had shorter noses and skulls slightly flattened at the back.

Furthermore, these characteristics had "an absolute correspondence" with those seen in humans, according to one of the Johns Hopkins team, Professor Roger Reeve. "The changes in the mouse face are in the same bones, in the same pattern, as in humans," he said.

Asked if the mouse model was good enough to reflect what goes on in humans, Professor Reeves said: "Yes. It's about the strongest parallel you can get.

"Nobody knows exactly why having too much of a chromosome would lead to the developmental problems you see with DS," said Professor Reeve. "We believe this model will help explain that in a way we couldn't before."

According to recently-published results from the team, the mouse model is so accurate that it has predicted a DS effect that scientists had not known about in humans. This concerns the small cerebellum, a part of the brain controlling movement, and the fact that DS-afflicted mice have a low density of brain cells in that area.