RESEARCH - When only one twin gets a disease

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Thursday, August 03, 2006

When Only One Twin Gets a Disease

Studying how gene expression differs in identical twins could shed

light on how genes and environment interact.

By Singer

Gene expression studies of identical twins could help explain why, in

some cases, only one of them gets a disease.

Identical twins share the same set of genes, such as ones for thick

eyelashes or a pointy nose -- as well as the genes that boost risk for

diseases. But sometimes rheumatoid arthritis, cancer, or another

malady strikes one twin and not the other. What leads to such

seemingly capricious twists of fate?

New research comparing gene expression in pairs of identical twins in

which only one twin has a disease is trying to answer that question,

looking at how the environment or other factors interact with genes to

increase disease risk.

One such study, published this month in the journal Arthritis and

Rheumatism, has identified three new genes involved in rheumatoid

arthritis. It could eventually shed light on the factors that trigger

the disease in genetically susceptible individuals.

Many diseases are caused by a combination of environmental and genetic

factors. In rheumatoid arthritis, for example, " an allergen or virus

might trigger in a genetically susceptible person the expression of

genes that cause inflammation and other problems, " says Matteson,

a rheumatologist at the Mayo Clinic in Rochester, NY.

Identical twins provide an ideal setting to study this complex

interaction. While they share the same genes, they sometimes differ in

how these genes are expressed. In the recent study, scientists at the

University of Michigan studied 11 pairs of twins in which one member

of the pair had rheumatoid arthritis, an auto-immune disease that

destroys the tissue lining the joints. Experts say that genetics

accounts for about 60 percent of the occurrences of the disease, while

other factors, such as infections or exposure to toxins, are

responsible for the remaining 40 percent. And both members of an

identical twin pair don't usually have the disease; if one twin has

it, the other will have it about 15 percent of the time. " That's a

strong indication that beyond genes, something else needs to happen, "

says ph Holoshitz, a rheumatologist at the University of Michigan

Medical School in Ann Arbor, who led the study. " What that is, we

still don't know. "

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Read the entire article here:

http://www.technologyreview.com/biomedicine/17249/page1/

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