( Daniel O’Connor M.D. Professor of Med...)Twin studies reveal genetic components leading to cardiac and kidney disease

"By studying many traits and genes, we have started to put together unexpected stories," he said.

Studying genetic variations in twins provides scientists with data on traits that are heritable, or passed down through human DNA, versus those determined by the environment, age or how a person cares for his or her health, factors such as medical care or diet and exercise. In a series of studies published in the American Heart Association journals Circulation and Hypertension, O’Connor has identified particular genes that influence human health in unexpected ways.

"Factors linked to cardiac or kidney disease ?such as hypertension, a tendency toward obesity or diabetes, elevated blood glucose and lipids ?were just amorphous risk factors before," said O’Connor. "Now we know that they run in families, not only because of a shared environment, but because they are determined in part by particular genes.

"Behavioral studies with twins have been conducted for decades, but in the post-genomic era, we can now factor in genotypes and determine the effect of specific genes on traits," O’Connor said. By studying both monzygotic (MZ, or genetically identical) and dizygotic (DZ, or fraternal, who share half of their genetic information) twin pairs, researchers can more readily pinpoint specific genes in people who are the same age. A formula measuring the difference in the frequency of traits between the siblings in each MZ and DZ twin pair establishes what is called the index of heritability.

The human genome has three billion base pairs and about 30,000 genes. O’Connor and his research team have looked at about 900 of these 30,000 genes.

"We’re just scratching the surface," he said.
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Source:University of California - San Diego