Wide variations in human genome unexpectedly found

Researchers at Brigham and Women’s Hospital (BWH) and Harvard Medical School (HMS) have found that the content of human DNA and genes, originally thought to be very similar among all human beings, differs significantly. This unexpected finding could one day provide researchers with the insight necessary to understand how disease development differs among individuals and could eventually lead to a deeper understanding of how to proactively prevent the development of particular diseases. Study results were published in Nature Genetics online on Sunday (Aug. 1).

Based on findings from the Human Genome Project, researchers and scientists believed that the DNA in the human genome, which encompasses the total set of genes carried by an individual, was almost identical among individuals. When beginning this study, researchers thought that results would confirm that among healthy individuals, 99.9 percent of their analyzed genetic material would be identical. Variations have been known to occur in the form of single base pair changes; however, in this study researchers found large-scale variations involving hundreds of thousands of base pairs of DNA.

According to the study’s senior author, BWH’s Charles Lee, assistant professor at HMS, “These results represent a discovery – one that helps complete our understanding of the human genome and that could contribute to the better understanding of human disease, including neurological disorders and cancer.”

To promote further understanding of the human genome, researchers from BWH, HMS, and Stephen Scherer, a scientist at The Hospital for Sick Children (HSC) in Toronto, compared the genomes of 55 healthy individuals, expecting to find little variation in their composition. Instead, researchers found more than 250 large fragments of DNA that differed among healthy individuals. These differences, called Large-scale Copy-number Variants or LCVs, reveal the human genome is much more dynamic than previously understood, and offer hope that further research will reveal certain LCVs as disease markers. In addition, many of these LCVs are in close proximity to “gaps” scientists have been unable to fill in the human genome. By studying LCVs more closely, scientists may be able to fill in some of these gaps, creating a more total picture of the foundation of human life.

“Several of these genetic variations overlapped with areas on the human genome currently associated with known diseases,” said first author of the study, A. John Iafrate, fellow in BWH’s Department of Pathology. “More research is required to better understand how to use this information to improve human health.”

For more information about the LCVs, visit the Genome Variation Database at http://projects.tcag.ca/variation.