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May 9, 2001

Finding disease genes may not be so difficult

By Patricia Reaney

LONDON, May 10 (Reuters) - Unraveling the secrets of the human genome, or the book of life, and pinpointing the genetic causes of common diseases could be easier than expected, American researchers said on Wednesday.

Scientists at the Whitehead Institute for Genome Research in Cambridge, Massachusetts who helped to map the three billion letters that make up the human genetic code have discovered that variations in human DNA that make people unique and prone to diseases are grouped together, sometimes in large blocks, and could be easier to trace than they had thought.

Their research is published in the science journal Nature.

The variations, called SNPs or single nucleotide polymorphisms, are single changes in the arrangement of those letters that make people different.

They hold the key to why some people are more susceptible to diseases such as cancer, diabetes or heart disease, the best way to treat them, how individuals will respond to different drugs and the genetic history of population.

"It will make decoding the human genome to understand diseases easier," David Reich said in a telephone interview.

By looking at different subsets of the genome of several people and comparing the results, researchers hope to identify variations that cause a propensity for certain diseases as well as their genetic basis.

So far, scientists have catalogued 1.4 million SNPs with their exact location on the human genome.

Reich and his colleagues found SNPs in large blocks in the northern European populations but not in people from Nigeria.

Because the SNPs are larger in some populations, they estimate that mapping the genes for common diseases will be easier. It may also not be necessary to identify every SNP before scientist can map genes for diseases.

"Our results have implications for disease gene mapping, suggesting a possible two-tiered strategy," Eric Lander, the director of the institute, said in a statement.

"The large blocks in northern European populations will help us easily map to first approximation the location of disease genes. And the presence in small blocks in other populations, like the Nigerians we studied, will allow us to hone in on the specific single letter differences responsible for a disease."

Using a technique called linkage disequilibrium mapping, the scientists hope to correlate a block of SNPs to its ancestral chromosome. So the larger the SNP blocks the easier it is to detect an area containing a disease gene.

Lander used the best-selling children's book Harry Potter and the Goblet of Fire to illustrate the idea.

He compared SNPs to spelling and word differences between the American and British editions of the books. Even if the two editions were mixed up, it would easy to determine which pages or lines came from which edition.

"Our results show that the shuffling at least in the northern European population has occurred in such a way that the blocks of interspersed text are large enough for us to trace them back to the original version," Lander said.

The scientists believe the SNP blocks are large in Northern Europeans because there was a demographic event about 27,000-53,000 years ago that had an impact on genetic history.

They suspect it could be due to the founding of Europe or the migration of people out of Africa to populate other areas of the world.

According to their findings, no more than 50 individuals gave rise to most of the modern northern European gene pool.

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