Genome Maps May Spot Disease In African Americans

Jul 21, 2011

Two independent teams of researchers have come up with the most accurate genetic maps ever made — a feat that should make the search for genes associated with diseases easier.

To understand why an accurate genetic map is useful, imagine you are trying to locate a house in Topeka, Kan., but the only map you have is one of the Interstate Highway System. You could probably find Topeka, but finding the specific house you want would take a lot of trial and error.

That's basically the situation researchers find themselves when they are search for a particular gene in the long stretches of DNA that make up our chromosomes. The trick to making a genetic map is to make road signs in DNA to tell you where you are.

John Novembre, a geneticist at UCLA, says one way to make road signs is to look for what are called recombination events.

"What you're trying to do is identify locations along the chromosome where the DNA that a person inherits from their mother is different from the DNA they inherited from their father," Novembre says.

And where that switch in a strand of DNA from one parent's DNA to the other parent's DNA is the recombination event.

But recombinations do not occur evenly across our genetic material, says David Reich, a geneticist at Harvard Medical School. Rather, he says, "they occur in very small hot spots." These specific hot spots become the road signs along the chromosomes that the researchers used to create the new genetic maps.

If all this is a scary reminder of what you didn't quite understand from high school biology, don't worry. The point is the map helps geneticists find their way.

Reich and his colleagues at Oxford University in England are publishing their map in Nature; Novembre and his UCLA colleagues published in Nature Genetics.

'Uniquely Informative' Information

What makes these genetic maps particularly interesting is they were developed using DNA from African Americans. Most maps created so far are based on DNA from people of European ancestry. Reich says using African American DNA revealed something unexpected.

"There's a family of about 2,500 hotspots of recombination that are active in people of West African ancestry like African Americans which are almost completely inactive in people of non-African ancestry," says Reich.

Finding these 2,500 hotspots could be particularly helpful for finding genes for diseases that are more common in African Americans.

"Researchers need maps that are matching the ancestry of their sample relatively closely, and so we're hoping that this map can actually serve as a great tool for disease mapping studies in African Americans," says David Wegmann, who collaborates with John Novembre at UCLA.

It hasn't always been easy to recruit African Americans to research studies. Herman Taylor heads the Jackson Heart Study, an effort to following the heart health of some 5,000 African Americans.

"History has shown that African Americans participating in large studies like ours didn't always get the most benefit," says Taylor. But he says that won't be the case with the Jackson Heart Study, or with the new mapping study. He's a co-author on the Harvard/Oxford study in Nature.

"Studying African American genetics gives unique information about African Americans, but also it is uniquely informative to genetics of the family of man," he says. Because Africa is thought to be the place where all modern humans originally came from, it's the DNA from African people that tells the first chapter in the story of modern human genetics.

"I think the people in the Jackson Heart study recognize that they have an important contribution to make," says Taylor. And with time, Taylor thinks their contribution will bring tangible benefits.

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