Analysis of Chromosome 7 Reveals Structures Linked to Diseases

A team of researchers from six institutions has sequenced 99.4% of chromosome 7, which has led to the discovery of structural features that appear to promote disease-causing genetic changes. The sequencing was reported in the July 10, 2003, issue of Nature.

Chromosome 7 is the largest chromosome sequenced to date. Previously, genome mapping techniques were developed on the chromosome, and it was the first chromosome to be searched by positional cloning in a successful hunt for the cystic fibrosis gene. During the current sequencing of the chromosome, researchers found that it contains an unusually high amount of duplicated sequence segments, and this duplication is much more extensive on the short arm of the chromosome. The reason for this remains unknown, although the researchers note that it may encourage the type of genetic deletions that cause disease.

This appears to be the case in Williams-Beuren syndrome, which is characterized by growth deficiency, heart disorders, and mild retardation. The syndrome is linked to very large deletions in a region of the long arm, which the new analysis shows to be a hotbed of duplicated segments. Such rearrangements of genetic material may occasionally help new genes to form, however. In all, about 1,150 protein-encoding genes were found on chromosome 7, about 20% less than predicted in a previous study by another team.

"Besides containing many genes that are crucial to development, this chromosome also hold the gene for cystic fibrosis and is frequently damaged in some types of leukemia and other cancers,” said Francis S. Collins, M.D., Ph.D., director of the US National Human Genome Research Institute (NHGRI, USA), which funded the study and also participated in the research. "This new analysis, coupled with our commitment to free and unrestricted access to sequence data, should further speed the discovery of genes on chromosome 7 related to human health and diseases.”




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