Thursday, November 23, 2006

Genetic breakthrough that reveals the differences between humans

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Scientists hail genetic discovery that will change human understanding

Scientists have discovered a dramatic variation in the genetic make-up of humans that could lead to a fundamental reappraisal of what causes incurable diseases and could provide a greater understanding of mankind.

The discovery has astonished scientists studying the human genome - the genetic recipe of man. Until now it was believed the variation between people was due largely to differences in the sequences of the individual " letters" of the genome.

It now appears much of the variation is explained instead by people having multiple copies of some key genes that make up the human genome.

Until now it was assumed that the human genome, or "book of life", is largely the same for everyone, save for a few spelling differences in some of the words. Instead, the findings suggest that the book contains entire sentences, paragraphs or even whole pages that are repeated any number of times.

The findings mean that instead of humanity being 99.9 per cent identical, as previously believed, we are at least 10 times more different between one another than once thought - which could explain why some people are prone to serious diseases.
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"I believe this research will change for ever the field of human genetics," said Professor James Lupski, a world authority on medical genetics at the Baylor College of Medicine in Houston, Texas.

Professor Lupski said the findings superseded the basic principles of human genetics that have been built up since the days of Gregor Mendel, the 19th century "father" of Mendelian genetics, and of Jim Watson and Francis Crick, who discovered the DNA double helix in 1953.

"One can no longer consider human traits as resulting primarily from [simple DNA] changes... With all respect to Watson and Crick, many Mendelian and complex traits, as well as sporadic diseases, may indeed result from structural variation of the genome," Professor Lupski said.
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But it is also becoming apparent that many diseases appear to be influenced by the number of copies of certain key genes, said Charles Lee, another of the project's leaders at the Brigham and Women's Hospital and Harvard Medical School in Boston, Massachusetts.

"Many examples of diseases resulting from changes in copy number are emerging. A recent review lists 17 conditions of the nervous system alone, including Parkinson's disease and Alzheimer's, that can result from such copy number changes," Professor Lee said. "Indeed, medical research will benefit enormously from this map, which provides new ways for identifying genes involved in common diseases," he said.
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There are just under 30,000 genes in the human genome, which consists of about 3 billion "letters" of the DNA code. The scientists found that more than 10 per cent of these genes appear to be multiplied in the 270 people who took part in the study. They do not know why some genes are copied and some are not. One gene, called CCL3L1, which is copied many times in people of African descent, appears to confer resistance to HIV. Another gene involved in making a blood protein is copied many times in people from south-east Asia and seems to help against malaria. Other research has shown that variation in the number of copies of some genes is involved in Alzheimer's and Parkinson's disease.
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Scientists from 13 research centres were involved, including Britain's Sanger Institute in Cambridge, which also took a lead role in deciphering the human genome. The research is published in Nature, Nature Genetics and Genome Research. The Independent (UK)

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