Language delay in early childhood can herald autism spectrum disorder. Now, a new study has discovered that such a language delay leaves a “signature” in the brain, through differences in brain volume.
The researchers, from the University of Cambridge in the UK, published their findings this month in the journal Cerebral Cortex.
Autism spectrum disorder (ASD) and autism are both general terms for a group of complex disorders of brain development. These disorders are characterized, in varying degrees, by difficulties in social interaction, verbal and nonverbal communication and repetitive behaviors.
With the May 2013 publication of the DSM-5 diagnostic manual, all autism disorders were merged into one umbrella diagnosis of ASD. Previously, they were recognized as distinct subtypes, including autistic disorder, childhood disintegrative disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS) and Asperger syndrome.
According to the Centers for Disease Control and Prevention (CDC), ASD occurs in about 1 in 68 children in the US, and it is five times more common in boys than girls. Appearing during early childhood, ASD does not typically carry with it identifying physical characteristics. However, those with the condition may communicate, behave and learn in ways that are different from the majority of other people.
Because there are no medical tests for doctors to employ when diagnosing ASD, they often assess the child’s behavior and development.
“Although people with autism share many features, they also have a number of key differences,” says lead author Dr. Meng-Chuan Lai, of the Cambridge Autism Research Centre. “Language development and ability is one major source of variation within autism. This new study will help us understand the substantial variety within the umbrella category of ‘autism spectrum.’”
In their latest investigation, the research team studied 80 adult men with autism – 38 of whom had delayed language onset – who were part of the Medical Research Council Autism Imaging Multicentre Study (AIMS).
Delayed language onset occurs when a child’s first meaningful words come out after 24 months of age, or when their first phrase occurs after 33 months.
Smaller brain volumes in men with language delay
The team found that the men who had delayed language onset also had less brain volume in several key regions of the brain including the temporal lobe, insula and ventral basal ganglia. Additionally, these men also had larger brainstem structures, compared with those who did not have delayed language onset.
The team also observed a link between current language function and a specific pattern of grey and white matter volume changes in key brain regions, including the temporal, frontal and cerebellar structures.
Dr. Lai says their study shows how the brains of autistic men differ, based on early language development and current language function, adding that this “suggests there are potentially long-lasting effects of delayed language onset on the brain in autism.”
The team acknowledges that the correlational study design does not allow them to infer causality. Thus, it is not possible to determine which came first – the language delays, or the changes in brain volume. However, ongoing longitudinal projects may be able to address this question, the researchers say.
Furthermore, these findings are consistent with previous studies, which have found key structural differences in the brains of autistic children. For instance, in a study published in August, researchers discovered that children and adolescents with autism have too many synapses in their brain due to a lack of pruning, which is thought to affect brain functioning. Another recent study suggests that early cerebellar injury may lead to the development of autism.
Autism: a single spectrum or discrete subgroups?
Less is known about the potential neurological differences between autistic children with varying degrees and types of symptoms. Future research, says Dr. Lai, should “move beyond investigating average differences in individuals with and without autism, and move towards identifying key dimensions of individual differences within the spectrum.”
The researchers note that the American Psychiatric Association removed Asperger Syndrome as a separate diagnosis from its diagnostic manual (DSM-5) last year, classifying it under ASD. This was a change that proved controversial within the medical community.
“This new study shows that a key feature of Asperger Syndrome, the absence of language delay, leaves a long-lasting neurobiological signature in the brain,” says senior author Prof. Simon Baron-Cohen. “Although we support the view that autism lies on a spectrum, subgroups based on developmental characteristics, such as Asperger Syndrome, warrant further study.”
“When asking: ‘Is autism a single spectrum or are there discrete subgroups?’…,” Dr. Lai says, “… the answer may be both.”