WEDNESDAY, Nov. 5, 2008 (HealthDay News) -- British researchers have identified the first gene to be associated with a common childhood language disorder.
Variants of the CNTNAP2 gene are associated with the disorder known as specific language impairment (SLI) -- the unexplained difficulty with language that can involve repetition of nonsense words, the researchers said.
The gene has also been implicated in autism and could represent a genetic link between the two disorders, the scientists said.
But the fact that this gene is also linked to other neurological conditions such as autism, epilepsy, schizophrenia and Tourette's syndrome means it may not be unique to language, but to the early development of cognitive function, said Rajesh Miranda, associate professor of neuroscience and experimental therapeutics at Texas A&M Health Science Center College of Medicine.
No one knows exactly how this gene may be affecting language.
"What skill in language-impaired children is this gene affecting?" said Dr. Karin Stromswold, author of an editorial accompanying the paper in the Nov. 6 issue of the New England Journal of Medicine. "There are a lot of reasons you can be language-impaired, excluding hearing loss and mental retardation."
Many children with common language impairment also have motor impairment, so the gene could actually be affecting either core language or motor involvement, said Stromswold, a professor of psychology and member of the Rutgers University Center for Cognitive Science, in New Brunswick, N.J.
An estimated seven percent of pre-school children have SLI, according to background information in the study.
Scientists had previously identified mutations in a gene known as FOXP2 as involved in speech disorders in one family.
"FOXP2 is the strongest gene candidate for language but the mutation is only seen in a small number of people, just one family, and that family also has mental retardation and other issues," Miranda said.
The FOXP2 gene is also active in animals such as mice, birds and primates that obviously don't have speech problems, Miranda said.
The authors of the new study, from the Wellcome Trust Centre for Human Genetics at the University of Oxford, screened this gene and found that one of the other genes it interacts with is called CNTNAP2. An analysis of CNTNAP2 function in 184 families with common language impairments found that children with certain forms of the gene had language deficits, notably nonsense-word repetition.
The findings seem to raise more questions than they answer, but hopefully they provide a gateway for further discoveries, experts said.
"A lot of times the clues to the basis of a disease come from very small groups," said Miranda. "You find one family that clues you into the process, but then you have to work through the process."
The American Speech-Language-Hearing Association has more on language development.