An international research consortium on Wednesday published the comprehensive catalog of human genetic variation, an achievement that will accelerate the search for genes involved in diseases and human evolution.

Organized as the International HapMap Consortium, more than 200 researchers from Canada, China, Japan, Nigeria, the United Kingdom and the United States described the initial results of charting the patterns of genetic variation that are common in the world's population. Their findings will appear in the Oct. 27 issue of the journal Nature.

The results provided overwhelming evidence that variation in the human genome is organized into local neighborhoods, called haplotypes, that usually are inherited as intact blocks of information. In the Nature paper, scientists described the Phase I HapMap, consisting of more than 1 million markers of genetic variation, called single nucleotide polymorphisms (SNPs).

Any two unrelated people are 99.9 percent identical at the genetic level. However, it is important to understand the 0.1 percent difference because it can help explain why one person is more susceptible to a disease or responds differently to a drug or an environmental factor than another person.

To discover tiny spelling variants out of the 3 billion letter DNA instruction book for humans, the researchers used DNA from blood samples collected from 269 volunteers from widely distributed geographic regions: Yoruba in Nigeria, Japanese in Tokyo, Han Chinese in Beijing, and Utah residents with ancestry from northern and western Europe.

The HapMap showed the boundaries of neighborhoods of correlated genetic variation, or haplotypes, across the entire human genome. With these haplotypes defined, the HapMap provides an efficient method for choosing "tag SNPs" that capture the genetic variation in each neighborhood with a minimum amount of work.

By using HapMap data to compare the SNP patterns of people affected by a disease with those of unaffected people, scientists can survey genetic variation across the whole genome and identify genetic contributions to common diseases far more efficiently than is possible with traditional approaches.

"This represents a milestone for medical research," said David Altshuler of the Broad Institute of Harvard and MIT, a lead scientist of the project. "Built upon the foundation laid by the human genome sequence, the HapMap provides a powerful new tool for exploring the root causes of common diseases."

"Such understanding is required for researchers to develop new and much-needed approaches to prevent, diagnose and treat diseases, such as diabetes, bipolar disorder, cancer and many others. "

The map will offer the scientific community an enormous savings,reducing the expense of searching the genome for hereditary factors in common disease by a factor of 10 to 20, and make possible research that was impractical only a few years ago, the researchers said.

In addition, the map can help to pinpoint genetic variations that may affect the response of people to medications, toxic substances and environmental factors.

Such information can be used to help doctors prescribe the right drug in the right dose for each patient, as well as recommend prevention strategies that take into account individuals ' varying responses to environmental factors. The map may be used to find genetic factors that contribute to good health, such as those protecting against infectious diseases or promoting longevity.

Also, the map has yielded fascinating clues into how our species evolved over time and specific forces that were important as the human population spread around the globe.

Genetic diversity in humans is increased by recombination, which is the swapping of DNA from the maternal and paternal lines. It has been recently realized that in humans, most such swapping occurs primarily at a limited number of "hotspots" in the genome.

By analyzing the HapMap data, the researchers have produced a genome-wide inventory of where recombination takes place. This will enable more detailed studies of this fundamental property of inheritance, as well as serve to improve the design of genetic studies of disease.

Source: Xinhua