British scientists say they've discovered the first gene tied to a language and speech disorder, raising hopes that the genetics revolution is closer to identifying the biological roots of conscious thought and, perhaps, refining what it means to be human.
The gene, FOXP2, is not specifically a gene that enables us to talk. Instead, researchers say they discovered a mutated form of the gene, which is responsible for a protein that enables the brain's language circuitry to function.
Some researchers suggest the discovery is a clue into the mechanics of cognitive thought, how adults develop from babies and even human evolution from lesser primates and other animals.
But others caution it would be wrong to heap too many expectations onto the damaged version of a single gene. Even the researchers who located FOXP2 say their discovery is just the beginning.
Their finding appears in the current issue of the journal Nature.
"We've identified one gene which will give us an entry point, and we're searching for others," said study author Tony Monaco, director of the Wellcome Trust Centre for Human Genetics at the University of Oxford. "It's really the first gene for behavioral genetics."
Researchers from the Oxford team and the Developmental Cognitive Neuroscience Unit of the Institute of Child Health in London studied three generations of a large family in England, identified only as the KEs. About half of its 24 members are affected with a speech disorder that impairs movement of the mouth, lips and tongue and also creates problems with phonemes and grammar, such as using proper word tense.
While some family members scored below average on nonverbal IQ tests, others did not. That led researchers to determine that low IQ was not a factor linked to the disorder. Researchers believe the mutation on FOXP2 is causing a breakdown in the gene's ability to regulate other genes, resulting in the disorder.
The researchers reached a breakthrough when they studied a person with the same disorder who was not related to the family. The gene in this individual, known as CS, is disrupted by a shift in DNA on chromosome 7, which highlighted the mutation for researchers. With the mutation located, researchers could look for the same mutation in the same place in the KE family.
"This gene controls other genes, and we need to find out which ones it's controlling," Monaco said. "We can then think about better therapies and diagnostic issues."
Once the mutation was identified, it was consistent in the KE family, lending weight to the researchers' conclusions, said Steven Pinker, of the Department of Brain and Cognitive Sciences at the Massachusetts Institute of Technology.
"When identifying a gene with a behavioral disorder it's unusual to find a contingency so perfect," Pinker said. "Everyone with the mutated version of the gene has the disorder and those without the mutated gene do not."
Pinker said he does not believe language impairments can be linked to one gene, but with this particular KE family, he said the FOXP2 gene does appear to be the core of the disorder.
Other researchers said it's also premature to link this study to the debate over whether a gene or genes are solely responsible for language in humans.
"I know everyone would like a nice simple, 'Yes, Eureka! We found it,"' said Bruce Tomblin, professor of speech pathology and audiology at the University of Iowa. "But it's not that simple."
Tomblin also was skeptical that speech and language disorders could be reduced to one element.
"To say there's a gene for speech and language may still be a risky step to take," he said.
This is not the first time the KEs have been research subjects. Other studies show they tend to have trouble controlling their hands and other motor skills, said Elizabeth Bates, director of the Center for Research in Language at the University of California, San Diego. To her, this suggests the genetic factors involve more than speech and language centers in the brain.
"This family does not have a disorder specific to language," she said. "Period."