for National Geographic News
The gene most closely linked to left-handedness has been found, experts announced this week.
The gene, called LRRTM1, is also associated with a slight increase in developing certain mental illnesses such as schizophrenia.
Clyde Francks is lead author of a new study on the gene and a visiting fellow at the Wellcome Trust Centre for Human Genetics at Oxford University.
For right-handed people, he said, the right side of the brain usually controls emotion, while the left side of the brain tends to control speech and language.
(Related: "First Ever Brain 'Atlas' Completed" [September 26, 2006].)
In left-handers—about 10 percent of the world's population—the pattern is usually reversed.
"We think that this gene affects the symmetry of the brain," Francks said. "LRRTM1 is not essential for left-handedness, but it can be a strong contributing factor."
Brain asymmetry is also a factor in schizophrenia, a mental disorder that affects about one in a hundred people worldwide and results in impaired perception and severe behavioral changes.
The researchers were not surprised when LRRTM1 also showed a possible impact on a person's chances of developing schizophrenia.
But Francks stressed that left-handers should not be unduly concerned about this link.
"There are many factors which make individuals more likely to develop schizophrenia," he said, "and the vast majority of left-handers will never develop a problem."
Francks and his colleagues discovered the LRRTM1 gene during a study of a hundred families with dyslexic children.
The team was initially searching for a link between dyslexia—a neurological learning disability—and whether a person was left- or right-handed.
When the researchers took genetic samples from all the families involved, they noticed that a particular chromosome showed a correlation with handedness.
"We then started to study the chromosome in detail and found this gene," said Francks, whose work appears in the July 31 online advance issue of the journal Molecular Psychiatry.
People appear to inherit the gene from their fathers (get an overview of human genetics).
The team now intends to study the gene to try and tease out its full purpose and function.
"We need to find out what role it plays in brain development and at what point it is active, whether it is during fetal development, childhood, or adulthood," Francks said.
Paul Corry, director of public affairs at Rethink, a U.K.-based mental health charity, agrees that more work needs to be done to determine how the gene affects mental health.
LRRTM1 "may turn out to be part of a complex relationship between a range of genes and environmental factors that lead to people developing schizophrenia," Corry said.
The gene could also help scientists understand more about how humans evolved.
Most animals have brains that are more symmetric, experts note, including our closest genetic relatives, the apes.
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