Language development is a truly remarkable phenomenon. But for a small number of kids, the words don’t come so easily.
Most children acquire their first words around 12 months of age, start to string words together by two years, and are able to talk in long and complex sentences by four years of age.
Learning to talk is remarkably robust. It has been said that short of being raised in a barrel (and perhaps even then), language development will march on with breathtaking ease and speed.
Specific Language Impairment
But for a minority of children, language development doesn’t progress with such efficiency, even if they have a “normal” level of intelligence, adequate hearing and no physical disability. To these children, we ascribe the diagnostic label Specific Language Impairment (SLI).
SLI is often first picked up by parents or teachers, who then refer to speech pathologists for a diagnosis. The prevalence of SLI in Australia is alarmingly high, with an estimated 5% of five-year-olds meeting the criteria for this disorder. Their difficulties can relate to expressing language (talking), understanding language, or both.
Still, SLI remains very much a “hidden disability” within the community – poorly understood and rarely discussed.
One reason for the lack of awareness about SLI is the very nature of the condition. Communication difficulties silence the biggest weapon for penetrating the public consciousness – advocacy. Add to this the fact that relatives of children with SLI often have communication difficulties themselves and the advocacy problem is exacerbated.
A second reason is SLI’s younger but more muscular brothers: developmental dyslexia and autism. The earliest descriptions of SLI date to the early 19th century, well before the first descriptions of developmental dyslexia (1887) and autism (1943). But, the intrigue of the symptoms associated with these latter conditions, in addition to the strong and numerous advocacy groups that support them, have facilitated increased research and greater public awareness.
A recent analysis of data from the National Institute of Health revealed that autism receives over 30 times more research funding than SLI, despite affecting five times fewer people.
What we know
In the mid-1970s, SLI was thought to be caused by any number of environmental insults, including inadequate parenting, subtle brain damage during birth, or recurrent ear disease. But there’s now good evidence that it involves a strong genetic component.
Advances in technology have facilitated the identification of a number of genes thought to be involved in the development of SLI, including the intensely studied CNTNAP2 gene (pronounced “catnap”) on chromosome 7q.
But like autism, it’s unlikely that just one gene causes the majority of SLI cases. Rather, it’s probably the case that multiple gene variants that, when combined (and perhaps in conjunction with environmental factors), cause language difficulties.
The effects of genes involved with SLI are likely to cause a different pattern of brain development. The enduring mystery of SLI is that no clear brain abnormality has been identified as a cause of language difficulties.
Promising research areas
Perhaps the most promising area of research for SLI investigates the “specialization” of the brain’s two hemispheres. In the majority of people, the most crucial areas involved in language production are found in the left hemisphere. Brain imaging studies have found that children and adults with SLI are more likely to have these language areas in the right hemisphere.
But like the genetic investigation of SLI, considerably more research is needed to really understand the neurological differences that underpin this condition.
Another area of particular interest is short-term memory. A series of experiments in the early 1990s found that children with SLI have considerable difficulty in accurately repeating nonsense words, such as perplisteronk and scriflunaflisstrop.
The inability to memorise previously unheard “words” and repeat them accurately is one possible reason why children with SLI have difficulty growing their vocabulary and stringing words together in complex grammatical structures.
Language development is highly variable and many children have early difficulties that resolve by the time they enter school. But when language difficulties persist into the school years - as in the case of children with SLI – there are often considerable longer-term effects.
Children with SLI are less likely to complete secondary school, and are more likely to experience long periods of unemployment during adulthood. What’s more, individuals with SLI have greater difficulties forming close friendships and romantic relationships.
The impact on mental health is significant, and adults with SLI are at a disturbingly high risk (around 50%) for depressive and anxiety disorders.
Prevalence figures suggest that there’s one child with unexplained language difficulties in every Australian school class. Understanding the causes of SLI is just a start – the major challenges are at the ground level.
Children with SLI require continued clinical and educational support to harness their clear talents and promote happy and healthy adult outcomes. Speech pathologists, teachers and parents are at the frontline of this battle. Our ability to help them lies in our willingness to advocate, understand, and ultimately, invest in this hidden disability.