An unprecedented genetic find has emerged from an extended British family in which more than half the members display a severe speech and language disorder. Scientists have now identified a genetic mutation that lies at the root of this family’s communication breakdown.
This is the first gene implicated in people’s capability to talk and to understand language, according to a team led by geneticist Cecilia S.L. Lai of the University of Oxford in England. She and her colleagues describe their discovery in the Oct. 4 Nature.
“It’s exciting that we’ve found a mutation common to every family member with this disorder,” says study coauthor Faraneh Vargha-Khadem, a neuroscientist at the Institute of Child Health in London. “This mutation may impede development of brain areas that mediate speech and language use.”
In the so-called KE family, 15 of 37 individuals across four generations display the same communication impairment. Their condition includes low verbal and spatial intelligence, difficulties in pronouncing a wide range of sounds, and grammatical deficits such as failing to grasp rules for forming the past tense of verbs, Vargha-Khadem says. In contrast, some other investigators view the KE family’s disorder as primarily a problem of grammar use. Scientists suggest that finding the genetic bases for the disorder may clarify its scope.
In earlier work, Vargha-Khadem and her coworkers isolated a distinctive segment of chromosome 7 containing about 100 genes, which is possessed only by KE family members who exhibit the disorder (SN: 1/31/98, p. 71).
In the new study, the researchers probed for changes in the suspect region of chromosome 7 in an individual outside the KE family who has the same communication disorder. This exercise led them to a specific gene, which had already been shown to regulate the activity of other genes involved in prenatal brain development.
Lai’s team then found that affected members of the KE family displayed a substitution of a single nucleotide in one of their two copies of that same gene. No such mutation appeared in unaffected family members or in 182 unrelated adults with no communication disorders.
These results won’t resolve the decades-long debate over whether genes map out grammar circuits in the brain or participate in a more general developmental process underlying language use. The gene’s specific influences on brain development remain unknown, Vargha-Khadem says.
The new finding provides “a smoking gun for a genetic cause of one kind of language disorder,” contends psychologist Steven Pinker of the Massachusetts Institute of Technology in a comment published in the same issue of Nature.
In contrast, psychologist Jeffrey Elman of the University of California, San Diego argues that the KE family’s genetic mutation fosters a range of perceptual and intellectual problems rather than harming language alone.