Communiqué de presse 

The decoding of the human chromosome 21

An international effort was initiated in 1995, as part of the Human Genome Project, to decode the genetic composition of the chromosome 21. This project was financed by public funds from the different participating countries. Most of the sequencing has been done in three laboratories in Germany and two laboratories in Japan. A few other laboratories from Switzerland, France, UK and USA participated in the collaboration by providing reagents, analyzing the data and characterizing genes. The Laboratory of Human Genetics of the University and Hospitals of Geneva directed by Professor Stylianos E Antonarakis, funded by the Swiss National Science Foundation participated in the project.

The different collaborative groups were able to decode with very high accuracy 33,500,000 nucleotides ("letters of the genetic alphabet") of the entire length of chromosome 21. A total of 225 active genes have been identified, and this number is considerably less than expected by the size of the chromosome. In addition, 59 dead and nonfunctional genes have been recognized. It was a surprise to note that a large portion of the chromosome (approximately one sixth of its size) does not contain any genes. The decoded nucleotide sequence of chromosome 21 has been deposited in public databases and is available to the world free of charge. No patents for the gene sequences have been deposited.

Chromosome 21 is the smallest human chromosome and consists of about 1% of the total human genome. It is a chromosome of considerable medical importance. An extra copy of this chromosome causes Down syndrome, the most common genetic disorder of mental retardation. In addition, it is the home of genes for several disorders including one form of epilepsy, early onset Alzheimer disease, deafness, blindness, neuropathies, autoimmunity, developmental defects, manic depressive illness, lipid abnormalities and leukemia.

The important milestone of deciphering all the nucleotide sequences of chromosome 21 will have profound implications for understanding the mechanisms of the disorders caused by the genes of the chromosome. It will also provide new diagnostic tools and the infrastructure for a better understanding of the evolution of our species. Most importantly, it will help both academic institutions and industry to develop novel therapies for numerous disorders.

The complete sequence and gene catalogue of human chromosome 21, Nature, 18 mai 2000, main writers: Y. Sakaki, N. Shimizu, A. Rosenthal, M.-L. Yaspo, H. Blàcker.

For more information, do not hesitate to contact:
the prof. Stylianos Antonarakis,tel 022 702 57 08 ou 702 57 07