A recent study by researchers in the ARC found that a common characteristic of autism – language delay in early childhood – is associated with anatomical differences in the brain in adulthood. The results are published in the journal Cerebral Cortex.
Delayed language onset – defined as when a child’s first meaningful words occur after 24 months of age, or their first phrase occurs after 33 months of age – is seen in a subgroup of children with autism, and is one of the clearest features triggering an assessment for developmental delay in children, including an assessment of autism.
The researchers studied 80 adult men with autism: 38 who had delayed language onset and 42 who did not. They found that language delay was associated with differences in brain volume in a number of key regions, including the temporal lobe, insula, and ventral basal ganglia, which were all smaller in those with language delay; and in brainstem structures, which were larger in those with delayed language onset.
Groups with and without early language delay showed equal amounts of current autistic features, but differed in social reciprocity shown early in life, and current language levels. The study found that current language function is associated with a specific pattern of grey and white matter volume changes in some key brain regions, particularly temporal, frontal and cerebellar structures.
“Although people with autism share many features, they also have a number of key differences,” said Dr Meng-Chuan Lai of the ARC, and the paper’s lead author. “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’. We need to move beyond investigating average differences in individuals with and without autism, and move towards identifying key dimensions of individual differences within the spectrum.”
Lack of language delay is a key distinguishing feature between Asperger Syndrome and Autism. The two conditions were combined in a single group termed “Autism Spectrum Disorders” in the new diagnostic manual (DSM-5) produced by the American Psychiatric Association, a decision that has been criticised by many researchers. This study may indicate that the differences between the two conditions may be more fundamental than previously assumed.
“It is important to note that we found both differences and shared features in individuals with autism who had or had not experienced language delay,” said Dr Lai. “When asking, ‘Is autism a single spectrum or are there discrete subgroups?’ the answer may be, ‘both’.”
He added, “We need to move beyond investigating average differences in individuals with and without autism, and move towards identifying key dimensions of individual differences within the spectrum.”
This study was supported by the Waterloo Foundation, the UK Medical Research Council (MRC), the Autism Research Trust, the Wellcome Trust, the William Binks Autism Neuroscience Fellowship, and the European Autism Interventions—a Multicentre Study for Developing New Medications (EU-AIMS).