Canadian-led project generates database of decoded DNA sequence of chromosome 7

Toronto, ON April 11, 2003 Scientists at the Hospital for Sick Children 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, was published yesterday in the online version of ‘Science’.

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," says Dr Stephen Scherer, who is lead author of the study, 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. "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,”

“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,” says Dr Johanna Rommens, who is 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.

This study revealed that chromosome 7 contains 158 million nucleotides of DNA (5% 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.

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.