The search for the causes of complex genetic diseases received a major boost today with the publication of the first map of human genetic variations, the subtle genetic changes that make each of us different from our neighbors.
Humans worldwide share 99.9% of their genetic blueprint. It is that 0.1% difference that makes each of us unique and that is the root of the genetic mischief that causes diseases such as diabetes, asthma, hypertension, cancer and a host of others.
In the past, researchers have had to sift through the entire 3 billion individual chemicals that comprise the human blueprint to search for disease-causing genes. But now it has become clear that each of those individual changes is linked to a large block of DNA, called a haplotype, that is generally inherited intact.
By focusing on haplotypes, researchers are able to reduce the number of sites that must be searched to a much more manageable 1 million, sharply speeding up the search for genetic change.
An international consortium of more than 200 researchers from six countries reported today at an American Society of Human Genetics meeting in Salt Lake City that they have completed a haplotype map, called a HapMap, using genetic information from 269 individuals from around the world. The map will be published Thursday in the journal Nature.
"The HapMap is a phenomenal tool that is making possible research that was impractical, if not unimaginable, only a few years ago," said Dr. Yusuke Nakamura of 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."
Identifying the genes that produce susceptibility to diseases like diabetes will lead to new techniques for diagnosis, treatment and, eventually, prevention, experts said.
Already, researchers using preliminary data from the HapMap have identified a gene that plays a key role in age-related macular degeneration, the leading cause of blindness among the elderly.
Teams in Japan, Canada and the United Kingdom have begun screening the haplotypes of individuals with a variety of diseases, comparing them to healthy control groups to identify genetic susceptibility; not only to chronic diseases such as hypertension and bipolar disorder, but also to infectious diseases such as tuberculosis and malaria.
"We will see an outpouring of discovery in the next two to three years," said Dr. Francis S. Collins, director of the National Human Genome Research Institute.
The team used DNA from blood samples collected from individuals worldwide, including Yoruba from Nigeria, Japanese from Tokyo, Han Chinese from Beijing, and Utah residents with ancestries from northern and western Europe.