In every classroom, roughly two children have developmental language disorder, a common neurodevelopmental condition. Children with this disorder typically have difficulties with using or understanding spoken language – and have had other possible causes such as hearing loss or autism spectrum conditions ruled out.
While a small proportion of children with developmental language disorder go through childhood with little to no problems, most tend to have some mental health difficulties. In our new study, published in the Journal of Speech, Language and Hearing Research, we have uncovered what might be the reason for this.
Developmental language disorder is sometimes referred to as an invisible disorder because it’s often misidentified or mislabelled in school. Children may be seen as shy, for example. But this probably stems from simply not being able to understand what the teacher is saying.
Children with developmental language disorder show symptoms from a whole range of problems. This includes emotional problems, such as being unhappy, and peer problems, such as being rather solitary. Some children also show signs of conduct problems such as lying and cheating and hyperactivity. What further complicates the issue is the range of problems these children show. Some children are affected in only one area, while others have a complex combination of emotional and behavioural symptoms.
The frequent mental health difficulties experienced by children with developmental language disorder are commonly thought to be caused by their struggles with language. This suggests that if we can support children with their language, then the mental health problems should resolve themselves.
It seems intuitive that children who are not able to express themselves verbally do so behaviourally. Or that language is a vehicle for social interactions, which are vital for developing support networks, which in turn act as a buffer against mental health problems. But maybe this isn’t the only explanation. What if, also, both language and mental health problems are affected by a third factor, genetics?
Our new study provides some support for this hypothesis. We used existing data from more than 5,000 children, who were already part of a large UK-based study, to investigate whether genetics might be driving both language and mental health difficulties.
We used a technique known as “polygenic scoring” – which adds up the effects of a large number of genetic variants for each individual in the study – to determine whether they are associated with children’s language and mental health difficulties. Parental responses to questionnaires and clinical assessments on children’s language ability were also used.
We looked at genetic variation across six genes that have previously been associated with language and found that, of the ones that were associated with language in our sample, nearly half were also associated with mental health difficulties, specifically peer problems. This suggests that language and mental health difficulties are linked genetically.
Our work provides very preliminary evidence that the genetic variants that are associated with language are also associated with mental health problems.
Our findings do not rule out the possibility that language problems cause mental health difficulties directly. But they seem to indicate that such difficulties arise because the genes that are responsible for building neural systems for language might also be responsible for mental health difficulties.
If our findings are confirmed in future work, they could have important implications for the timing of mental health interventions for children with developmental language disorder. Indeed, while some developmental delays might improve, it would make sense to intervene before children start showing symptoms of poor mental health.