Project Will Map Genetic Variations

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Project Will Map Genetic Variations

Tue Oct 29, 3:50 PM ET

By PAUL RECER, AP Science Writer

WASHINGTON (AP) - Looking for a quicker way to identify genes that cause

disease, researchers are beginning a $100 million effort to identify blocks

of DNA that contain common variations in the human genetic structure,

officials announced Tuesday.

The project, expected to take three years, involves nine research groups in

five countries and will analyze genetic patterns in blood samples taken from

people in Nigeria, Japan and China and from people of northern and western

European ancestry in the United States.

The goal is to determine how the 3 billion bits of DNA in the human genome

(news - web sites), or genetic structure, are organized into sequence

variations, or haplotype blocks, that are shared by many people.

Once these haplotypes are mapped, it will form " a powerful and elegant

shortcut " to identifying inherited gene sequences linked to disorders such

as diabetes, heart disease and cancer, said Dr. Francis , head of the

National Human Genome Research Institute, one of the National Institutes of

Health (news - web sites).

" This work will have a profound impact on the future of medicine, "

said at a news conference announcing the project. He called the effort the

International HapMap Project.

Both public and private labs are participating, with many of the same

researchers who helped complete the sequencing in 2001 of the human genome.

The human genome comprises about 3 billion pairs of DNA. Each pair is made

up of chemicals commonly identified with the letters A, T, C or G. Virtually

all the letters are in the same sequence in everyone, but there are an

estimated 10 million " spelling " differences, involving a single change where

one DNA letter is replaced by another. These are called single nucleotide

polymorphisms, or SNPs, and some are thought to be related to disease.

Recent studies have shown that SNPs are organized into DNA neighborhoods

called haplotype blocks comprising about 10,000 or more base pairs. Many

people share the same haplotype blocks, and common variations are found in

virtually all populations. Thus, it is possible to identify a haplotype

block by finding a single SNP, instead of a having to check all 10,000 base

pairs. In effect, the HapMap project is an effort to find DNA landmarks that

identify specific DNA sequences shared by many people. Later research would

then look within those sequences to find the genes that cause disease.

As an illustration of how the HapMap would help find disease genes,

related it to leaky gas pipes. Suppose, he said, a safety officer knows

there are 12 leaking gas pipes somewhere in a city and must quickly find

them. It could take years to systematically search the city house by house,

said . It would be much quicker for the safety officer first to

identify blocks within the city where there are known to be gas leaks, then

limit his house-to-house search to those blocks.

By breaking up the human genome into blocks with known genetic variations,

researchers can go directly to those blocks and search for disease genes

instead of having to search through all 3 billion DNA base pairs, he said.

For instance, if researchers could find a specific haplotype block linked to

diabetes, they could focus their search for a diabetes gene to that block

instead of having to survey the entire human genome.

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On the Net: National Human Genome Research Institute:

http://www.nhgri.nih.gov/