Researchers in England have identified the first gene to be linked to language and speech, suggesting that our human urge to babble and chat is innate, and that our linguistic abilities are at least partially hardwired.
"It is important to realize that this is a gene associated with language, not the gene," said Anthony Monaco of the University of Oxford, England, who led the genetic aspects of the study.
The gene is required during early embryonic development for formation of brain regions associated with speech and language.
The gene, called FOXP2, was identified through studies of a severe speech and language disorder that affects almost half the members of a large family, identified only as "KE." Individuals with the disorder are unable to select and produce the fine movements with the tongue and lips that are necessary to speak clearly.
"The most obvious feature is that they are unintelligible both to naive listeners and to other KE family members without the disorder," said neurologist Faraneh Vargha-Khadem of London's Institute for Child Health, who studied the family. The members of the family also have dyslexic tendencies, difficulty processing sentences, and poor spelling and grammar.
FOXP2 is responsible for the rare disorder seen in the KE family that is a unique mixture of motor and language impediments, said Monaco.
But, Monaco cautioned, "FOXP2 is unlikely to be the cause of less severe language deficits that affect approximately 4 percent of schoolchildren. FOXP2 will not be the major gene involved in most of these cases."
Their findings are published in the October 4 issue of the journal Nature.
Using data from the KE family, researchers narrowed the location of the FOXP2 gene to a region of chromosome 7 that contained about 70 genes. Analyzing these genes one by one is a task that could easily have taken more than a year. But Monaco's team made a breakthrough when researcher Jane Hurst of Oxford Radcliffe Hospital identified a British boy, unrelated to the KE family, who had an almost identical language deficit.
The boy, known as "CS," had a visible defect in chromosome 7 that specifically affected the FOXP2 gene. "The defect was like a signpost, precisely highlighting the gene responsible for the speech disorder," said Monaco.
The FOXP2 gene produces a protein called a transcription factor, which attaches itself to other regions of DNA and switches genes on and off.
In the KE family, one of 2,500 units of DNA that make up the FOXP2 gene is mutated. Monaco suggested that this mutation prevents FOXP2 from activating the normal sequence of genes required for early brain development.
"It is extraordinary that such a minute change in the gene is sufficient to disrupt a faculty as vital as language," he said.
Although humans have two copies of every gene, just one mutated copy of FOXP2—as in the case of both CS and the KE family—can have devastating effects on brain development, said Vargha-Khadem.
Brain imaging studies of the KE family revealed that affected members have abnormal basal ganglia—a region in the brain involved with movement—which could explain difficulty in moving the lips and tongue. Regions of the cortex involved in speech and language also appear aberrant.
The discovery of FOXP2 offers Monaco and other geneticists a probe to fish for other genes involved in development—specifically those directly controlled by FOXP2.
Also in progress is a collaborative project to study the evolution of the human FOXP2 gene by comparing it with versions in chimps and other primates. Monaco speculates that differences between the FOXP2 gene in humans and chimps may reveal a genetic basis for differing abilities to communicate.
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References:
Trivedi Bijal P. 2001. "Scientists Identify a Language Gene". National Geographic. Posted: October 4, 2001. Available online: http://news.nationalgeographic.com/news/2001/10/1004_TVlanguagegene.html
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