Most children have mastered the complexities of spoken language by age six or seven,. But about 5% of otherwise healthy children struggle with either expressing themselves, understanding what others are saying or both, a disorder known as specific language impairment (SLI).
In a report published online yesterday by the New England Journal of Medicine, researchers from the Wellcome Trust Centre for Human Genetics at the University of Oxford present evidence that a gene called CNTNAP2 is involved in specific language impairment.
“It has long been suspected that inherited factors play an important role in childhood language disorders,” Simon Fisher, senior author of the study, said in a statement. “But this is the first time that we have been able to implicate variants of a specific gene in common forms of language impairment.”
Several previous studies have linked broad regions of DNA with SLI, but there has yet to be any consensus on the true genetic underpinnings of the disorder.
The researchers narrowed in on the role of CNTNAP2 in SLI because it interacts with FOXP2, another gene implicated in the development of language skills. Some people with rare speech disorders have mutations in FOXP2, but variations in this gene have not been associated with more typical forms of language impairment.
In a study of children from 184 families with at least one child affected by SLI, the researchers found that each G at decreased the score on a test that measures the ability to hear and repeat nonsense words like “brufid” and “contramponist” by 5.53 points on average. Previous studies have indicated that this test is a good indicator of SLI.
Each G also decreased a child’s score on the standardized Expressive Language Score, which measures the ability to communicate through spoken language, by an average 3.21 points. Scores can range from 46 to 141 for the nonsense word test, and 50 to 150 for the expressive language test. Most children in the general population get a score between 85 and 115 on both.
Variants in the same region of CNTNAP2 as have also been linked to delayed speech in children with autism. Some experts suggest that the different components of autism-spectrum disorders, such as communication problems, impaired social interaction, and repetitive behaviors, could be due to different genetic influences. Fisher and colleagues suggest that alterations in CNTNAP2 could be a shared mechanism for pure SLI and language problems associated with autism.
The research team plans to investigate whether variants of CNTNAP2 are linked to natural variations in linguistic abilities in the general population. They also plan to investigate other genes that interact with FOXP2.
“Genes like CNTNAP2 and FOXP2 are giving us an exciting new molecular perspective on speech and language development, one of the most fascinating but mysterious aspects of being human,” said Fisher. “This work promises to shed light on how networks of genes help to build a language-ready brain.”
In an accompanying editorial in NEJM, Karin Stromswold, who was not associated with the research, said that the findings of the British study and others like it could someday help tease apart the genetic and environmental factors that affect language and language disorders. Stromswold questioned, however, why others studies of SLI have never implicated the DNA region where CNTNAP2 is found, even when the same group of children was studied.