DNA sequence of chromosome 7 decoded

Canadian-led project generates database with medical annotation available to the public

Scientists at The Hospital for Sick Children (HSC) have compiled the complete DNA sequence of human chromosome 7 and decoded nearly all of the genes on this medically important portion of the human genome. The research, which involved an international collaboration of 90 scientists from 10 countries, publishes in the online version of the scientific journal Science on April 10, 2003.

Two years ago, a draft (or fragmented) human genome DNA sequence was published by the public Human Genome Project, and separately by Celera Genomics. To coincide with celebrations of the 50th anniversary of the discovery of the structure of DNA, the DNA sequencing phase of the Human Genome Project will be declared completed in April.

“In a massive study, we combined all information in public and private databases, including data generated by Celera Genomics, as well 15 years of our data and analyses to generate what we believe is the most comprehensive description of any human chromosome. Chromosome 7 is often referred to as ’Canada’s chromosome’ because of this country’s major contribution to the mapping and identification of many important disease genes on that chromosome over many years,” said the study’s lead author Dr. Stephen Scherer, a senior scientist at The Hospital for Sick Children and an associate professor in the Department of Molecular and Medical Genetics at the University of Toronto (U of T).

“This is the first time that a significant effort has been made to incorporate medical observations with DNA sequence as part of genomic research, which will make it accessible and useful to health-care professionals and researchers outside of the genomics field,” said Dr. Johanna Rommens, a study co-author, interim head of the Genetics and Genomic Biology Research Program at HSC, and an associate professor in the Department of Molecular and Medical Genetics at U of T.

There are 23 pairs of chromosomes in the human genome and each person inherits one of each set from their parents. The chromosomes encode genes that control all aspects of human development including some behavioural characteristics.

This study revealed that chromosome 7 contains 158 million nucleotides of DNA (5 per cent of the genome) and 1,455 genes (of the estimated 28,000 protein-coding genes in the human genome), some of which cause diseases such as cystic fibrosis, leukemia, and autism. The project also describes discoveries of sites along the chromosome where invading viruses integrate, ’fragile’ regions prone to breakage, areas called ’gene jungles’ and ’gene deserts’, as well as primate-specific genes.

In the study, all medically relevant landmarks along the chromosome were identified, including the several hundred chromosome breakpoints where disease-related mutations occur. The breakpoints found in autism patients were used to pinpoint specific genes associated with the disorder.

The information generated by the chromosome 7 project has been established in a publicly accessible database that can be used to facilitate disease gene research. For example, a physician can enter the genetic deletions found in a patient and the known phenotypes (manifestations of the genetic mutation) are identified. The chromosome 7 database is available at www.chr7.org (the site is publicly accessible after the journal embargo lifts).

Dr. Martin Godbout, president and CEO of Genome Canada said, “This work represents an unprecedented Canadian contribution to the Human Genome Project. More importantly, it exemplifies how genetic, genomic, and clinician scientists in the public and private sectors worldwide can work together in a common goal to understand the human genome and its role in health and disease.”

This research was supported by Genome Canada through the Ontario Genomics Institute, the Canadian Institutes of Health Research, the Canadian Genetic Diseases Network, The Centre for Applied Genomics at The Hospital for Sick Children, and The Hospital for Sick Children Foundation. Dr. Scherer is an Investigator of the Canadian Institutes of Health Research and International Scholar of the Howard Hughes Medical Institute.

The Hospital for Sick Children, affiliated with the University of Toronto, is Canada’s most research-intensive hospital and the largest centre dedicated to improving children’s health in the country. Its mission is to provide the best in family-centred, compassionate care, to lead in scientific and clinical advancement, and to prepare the next generation of leaders in child health. For more information, please visit http://www.sickkids.ca.

For more information, please contact:
Laura Greer, Public Affairs
The Hospital for Sick Children
416-813-5046
laura.greer@sickkids.ca

Anie Perrault
Vice-President, Communications
Genome Canada
613-751-4460 ext. 13
aperrault@genomecanda.ca