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Twin Study Suggests Right-
Handedness Is Gene-Based



NEW YORK (Reuters Health) - A new study of twins bolsters the belief that there may be a gene that distinguishes righties from lefties, and perhaps influences the structure and function of their brains as well.

California researchers examined 72 pairs of identical twins, who share all of the same genes, and 67 pairs of fraternal twins, who share many but not all genes. All were World War II veterans enrolled in a long-term government brain study, and their average age was 72. All patients underwent MRI scans to compare the sizes of the left and right sides of their brains.

The scans indicated that righties had less symmetrical brains than the lefties, as has been shown in previous research, Dr. Daniel Geschwind and colleagues report in the March 5th issue of the Proceedings of the National Academy of Sciences.

And when the researchers compared individual pairs of identical and fraternal twins, they found that the brains of the right-handed identical siblings were the most similar structurally, suggesting a strong genetic underpinning to right-handedness that does not seem to be present for left-handedness.

"The brain structure differences in right-handers seem to have a significant genetic component," said Geschwind, director of the neurogenetics program at University of California, Los Angeles. "We've shown this for the first time."

Geschwind told Reuters Health that previous studies have found that nearly all right-handers have language function based in the left side of the brain. But this is only the case in about 60% of lefties; the others have language function based in the right half of the brain or shared between the two.

Studies also have indicated that while many lefties are gifted at mathematics, architecture and music, they also tend to be more likely to have stuttering problems, dyslexia and autism, Geschwind noted.

"Being left-handed clearly has many advantages," he said. "It can also reflect a greater susceptibility to language-based learning disorders."

As a result, studies like this one are important for researchers trying to understand how left- or right-handedness relates to brain functioning and for those hoping to develop new therapies for speech disorders, he said.

SOURCE: Proceedings of the National Academy of Sciences 2002;99:3176-


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