A map (HapMap) of genetic variation in human genome, which could lead to the discovery of genes involved in many diseases such as asthma, diabetes, cancer and heart disease has been completed by a multinational organization called the International HapMap Consortium.
In the article published in the Oct. 27 issue of the journal Nature, more than 200 researchers from Canada, China, Japan, Nigeria, the United Kingdom and United States report the common patterns of genetic variations in the world population.
The article reveals that the human genome variations are organized in certain parts of DNA called haplotypes, which usually are inherited as intact blocks.
The constructing of the human haplotype map (HapMap) began in Oct. 2002. The DNA samples were collected from 269 volunteers, from widely distributed geographic regions, representing four different races including Yoruba in Ibadan, Nigeria, Japanese in Tokyo, Han Chinese in Beijing, and Utah residents with ancestry from northern and western Europe.
The so-called Phase I HapMap consists of more than one million markers of genetic variation called single nucleotide polymorphisms (SNPs). The Phase II HapMap will be finished soon, which will add more than two million more SNPs to the Phase I HapMap.
"This represents a milestone for medical research. 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," said David Altshuler, M.D., Ph.D., a corresponding author of the study from The Broad Institute of Harvard and MIT in Cambridge, Mass. "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."
According to the study, any two unrelated people share 99.9 percent DNA or genes. The remaining 0.1 percent is crucial in understanding why one person is more susceptible to certain disease than another, or one responds to a drug or environmental factor differently.
With the Map, the SNP patterns of those with and without a particular disease can be easily compared, the whole genome for the genetic variation can be surveyed, and the genetic contributions to the disease can be localized.
"The HapMap is a phenomenal tool that is making possible research that was impractical, if not unimaginable, only a few years ago," said Yusuke Nakamura, M.D., Ph.D., an author from the University of Tokyo's Human Genome Center. "It offers 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."
The HapMap has already found applications before completion. In a study reported in March in the journal Science, HapMap data was used to uncover a genetic variation that is related to an increased risk of age-related macular degeneration, the leading cause of severe vision loss in the elderly.
The HapMap can help discover genetic variation for other common diseases, including diabetes, Alzheimer's disease, cancer, schizophrenia, asthma, hypertension and heart disease. More than 70 studies presented at a recent meeting of the American Society of Human Genetics in Salt Lake City were related to the HapMap.
Other than helping identify genetic variation for diseases, the HapMap can also pinpoint genetic variations that may determine the individual response to medications, toxic substances, and environmental factors. Such information can help find better treatments or prevention strategies for certain diseases. In addition, the HapMap can also be helpful in finding genetic factors that contribute to good health, such as longevity.
Using the Phase I HapMap, scientists have already learned how our species evolved over time. The Map has helped construct an inventory of genetic recombination involving maternal and paternal chromosomes, which leads to genetic diversity in humans. The HapMap is also useful in searching the genes responsible for immune response and neurological processes.
The authors of the study cautioned the use of the HapMap to search genes associated with human health and disease. "Rigorous standards of statistical significance will be needed to avoid a flood of false positive results," wrote the authors.
Among the one million SNPa in the HapMap, there are five exclusive differences among human's 22 pairs of non-sex chromosomes between the Yoruba and the Japanese/Han Chinese people; 11 between the Yoruba and Utah people with northern and western European ancestry; and 21 between the Utah and Japanese/Han Chinese people.
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