LONDON (Nov. 22) - One person's DNA code can be as much as 10 percent different from another's, researchers said on Wednesday in a finding that questions the idea that everyone on Earth is 99.9 percent identical genetically.
They said their new version of the human genetic map, or "book of life," fills in many missing pages and chapters to explain how genes are involved in common diseases.
"This important work will help identify genetic causes of many diseases," Dr. Mark Walport, director of Britain's Wellcome Trust, said in a statement.
Instead of showing single variations in human DNA that make people unique, the map looks at differences in duplications and deletions of large DNA segments known as copy number variants or CNVs, which can help explain why some people are susceptible to illnesses such as AIDS and others are not.
"We're a patchwork of DNA sequences, gains and losses," Dr. Charles Lee of the Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts told a news conference
Scientists from more than a dozen centers around the world identified about 3,000 genes with variations in the number of copies of specific DNA segments. The changes can affect gene activity, including susceptibility to diseases.
The Human Genome Project mapped the billions of letters that make up the human genetic code. Scientists later refined the map by looking for single variations called SNPs or single nucleotide polymorphisms.
The CNV map gives researchers a different way to look for genes linked to diseases by identifying gains, losses and alterations in the genome.
"We estimate this to be at least 12 percent of the genome, similar in extent to SNPs. This has never been shown before," said Dr. Matthew Hurles of Britain's Wellcome Trust Sanger Institute.
He said that resistance to infection by HIV, the virus that causes AIDS, is determined in part by multiple copies of the gene CCL3L1, which cannot be seen on an SNP map.
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The scientists, whose findings are reported in the journals Nature, Nature Genetics and Genome Research, compiled the CNV map by comparing DNA from 270 healthy people in China, Japan, Nigeria and the United States.
The consortium identified 1,447 different CNVs that covered about 12 percent of the human genome. About 285 of them are associated with diseases, including schizophrenia, psoriasis, coronary heart disease and congenital cataracts.
"With these new tools, we and our clinical colleagues are able to find previously undetectable deletions or duplications of the genome in a patient. The CNV map now allows us to identify which of these changes are unique to the disease," said Dr. Nigel Carter, of the Wellcome Trust Sanger Institute.Genes important to the immune system and to brain development and activity tend to have many CNVs, the researchers said. These are functions that have evolved rapidly in humans.
"I believe this paper will change forever the field of human genetics," said James Lupski, vice chair of the Department of Molecular and Human Genetics at the Baylor College of Medicine in Houston, Texas.
"One can no longer consider human traits as resulting primarily from single base-pair changes or influenced only by SNPs."
The scientists set up an Internet database to encourage researchers around the world to share information on patients with CNV details.
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