On the Track to Understanding the Molecular Causes of the Down Syndrome

Gene Expression Map of the Human chromosome 21 Orthologues in the mouse

People with "Down Syndrome" have three instead of two chromosomes 21 in their cells. Therefore scientists have named this condition "Trisomy 21". Trisomy 21 is the most frequent genetic cause of mental retardation in humans.

In cooperation with international partners, scientists of the German National Genome Research Network (NGFN) and the German Human Genome Project (DHGP) headed by Dr. Marie-Laure Yaspo investigated the activity of 160 genes which are located on the human chromosome 21. The scientists used an animal model, the mouse, for their comprehensive analysis. When the mouse genome was deciphered it was found that mouse and man have a similiar set of genes, most of them having the same functions. The genes of the human chromosome 21 are located on the mouse chromosomes 10, 16 and 17. The results were catalogued in a "gene expression atlas" that will be a valuable tool for investigating why the additional genes on the extra copy of chromosome 21 cause certain diseases such as Down Syndrome.

These diseases are thought to result from an overdose of those cell components whose building instruction is encoded on the chromosome 21. Scientists identified several genes that are specifically expressed in the heart and could be responsible for the heart malformations frequently found in patients with Down Syndrome. However, about 70 percent of the genes of chromosome 21 are paticularly active in the brain, which might explain why mental retardation represents the main symptom of the Down Syndrome.

The results are published in the scientific journal "Nature" (Nature, issue December 2002, volume 5;420, Nr. 6915, pages 586-90).