Scientists plan to refine map of human DNA

Hopkins, others begin $100 million project in search for disease genes

October 30, 2002|By Michael Stroh | Michael Stroh,SUN STAFF

In an effort to speed the search for the genes underlying disease, the Johns Hopkins University and an international consortium of scientists are embarking on a $100 million effort to create a next-generation map of human DNA.

The venture, dubbed the International HapMap Project, is expected to take three years and involves public and private research centers in six countries. Its goal: to help scientists nail down the genetic components of complex and often deadly conditions such as asthma, cancer, diabetes, heart disease and schizophrenia - a scientific quest that has so far proved frustratingly elusive.

"This work will have a profound impact on the future of medicine," Dr. Francis Collins, director of the National Human Genome Research Institute, said yesterday at a Bethesda news conference announcing the effort.

In addition to new cures and diagnostic tests, the map might also shed light on mysteries of human history and evolution, the record of which is often recorded in DNA, Collins said.

The need for a more refined genetic map arises from a simple reality: The human genome is vast - composed of more than 3 billion pairs of chemical building blocks, which were decoded by scientists last year.

While researchers have found that the building blocks in any two people are more than 99.9 percent identical, the remaining 0.1 percent has become the focus of intense study.

These individual genetic variations - about 10 million in all - determine not only characteristics such as eye color and blood type, but how susceptible a person is to a particular disease, scientists say.

By studying families and comparing the sick to the healthy, researchers over the years have successfully ferreted out the underlying genetic causes of disorders such as Huntington's disease or cystic fibrosis. But these conditions are relatively rare and involve only a single gene.

So far, family histories and other familiar tools have failed to explain the genetic underpinnings of more common maladies such as Alzheimer's disease, arthritis, cancer, diabetes, schizophrenia and stroke - diseases thought to result from subtle changes in perhaps dozens of genes. To complicate matters, the environment is also thought to play a role.

"The problem is basically a lot harder than people had hoped it would be," Collins said.

To make finding disease genes easier, researchers will divide the genome into smaller chunks, known as haplotypes - thus the project's name, HapMap.

"We expect these genetic chunks to hold clues about the subtle genetic influences that result in complex diseases," said Aravinda Chakravarti, the director of the McKusick-Nathans Institute of Genetic Medicine who is leading the project at Hopkins.

Scientists will create the map by collecting as many as 400 DNA samples from four different groups from around the world - Yorubas in Nigeria, Japanese, Han Chinese, and U.S. residents of Northern and Western European ancestry.

Project organizers say the ethnic groups were picked for both practical and scientific reasons, chiefly so the map would contain the widest variety of genetic differences. Officials stress that no medical or personal identifying information will be obtained from the volunteers providing the samples.

Hopkins and other groups will then carve the DNA into chunks, much as ZIP codes subdivide the United States. So, rather than searching through all 3 billion chemical components to find a quirk - a time-consuming and costly process - scientists using the new map can quickly zero in on the genetic neighborhood where a disease gene resides.

Dr. David Valle, a pediatrician at Hopkins who is studying the genetic roots of schizophrenia and other diseases, said he thinks the completed map will help him and others make headway on conditions that have stymied scientists.

"We think it's going to be a major shortcut," he said. "It will allow me to do studies that I could only imagine before."

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