A common language disorder that affects one in 14 children has been linked to a gene for the first time, offering insights that ultimately promise better diagnosis and treatment.

Variations in a gene called CNTNAP2 are associated with specific language impairment (SLI), which causes communication difficulties in about 7 per cent of children, British scientists have found.

The work, led by Simon Fisher, of the University of Oxford, could eventually help thousands of families affected by the condition, which causes delayed speech, poor comprehension of language, and an inability to link words into grammatical structures and sentences.

Intellectual, physical and emotional development is otherwise normal, though many children with SLI have behavioural and educational problems triggered by their difficulties in expressing themselves and making friends.

Though SLI is more common than other developmental disorders such as dyslexia and autism, there is much less awareness of the problem among parents, pre-school teachers and health professionals, and it is often missed or misdiagnosed.

It has long been suspected that genes are involved, but Dr Fisher’s team is the first to identify one with a clear link to the condition. Many others are also likely to be implicated.

He told The Times that he hopes such discoveries can be used to identify separate types of SLI that respond to different methods of speech and language therapy, or even to drugs.

“Any new information will be helpful because at the moment, it’s very difficult to sub-type SLI,” Dr Fisher said. “It would be good to identify people who are at risk, because early identification is really important. It seems to be one of the most effective ways of actually improving outcomes, through speech and langauge therapy.

“There isn’t a magic bullet, but we’re hoping that by understanding the biology more it’ll help people to come up with new therapies. If you can identify pathways in the brain that contribute, you might be able to figure out how to improve them.”

The discovery, which is published in the New England Journal of Medicine has emerged from studies of another language-related gene called FOXP2. This gene is a biological “master switch” that causes severe but rare communication defects when it goes wrong.

FOXP2 was identified in 2001 from a British family known by the initials “KE”. About half of its members have a severe language defect that leaves them struggling to form and identify speech sounds, to construct sentences and to understand grammar. People unfamiliar with the family find it difficult to make sense of what affected members say.

While FOXP2 mutations and the condition they cause are very rare, it belongs to a class of genes known as transcription factors, which regulate the activity of other genes. Dr Fisher has now exploited this quality to search for these downstream genes, and to test them for links to SLI, a much more common disorder.

One of the most intriguing downstream genes identified so far was CNTNAP2, which was already known to be important to the interaction of nerve cells in the developing brain. A study of 184 families with SLI has now found that certain variants of this gene significantly raise the risk of the disorder.

What’s great about FOXP2 is that even though the mutations are very rare, we know that when people have a mutation it severely messes with their speech,” Dr Fisher said. “It gives us a window into the biology.

“FOXP2 is a regulatory factor that is switching off other genes. Even though FOXP2 is not itself mutated or involved in other cases of language impairment, the downstream pathways that it switches on and off might be.

“So what we’ve been doing is to figure out what these pathways are. We’ve been able to look and see what are the genes that FOXP2 is regulating. CNTNAP2 is the first one we have been investigated in SLI, and it looks like it is indeed involved in common language deficits. We’d like now to examine other FOXP2 targets in a similar way.”

The research has not yet revealed how the gene interferes with language development, but there are clues. As it makes a type of protein called a neurexin, which is involved in wiring up the nervous system, this may malfunction.

“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,” Dr Fisher said. “There are likely to be more answers buried in our genome. This work promises to shed light on how networks of genes help to build a language-ready brain.”

Other studies have implicated CNTNAP2 in autism. “Our findings suggest that similar changes in the regulation or function of this gene could be involved in language deficits in both SLI and autism,” Dr Fisher said. “This supports the emerging view that autism involves the convergence of a number of distinct problems underpinned by different genetic effects.”

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