Subtypes Of Autism Linked To Brain Structures, Study Finds

Understanding how the autistic brain develops could lead to new therapies. Image:

Children with autism spectrum disorder (ASD) tend to have larger brains than their non-autistic counterparts, although intriguingly this correlation is seen predominantly in boys. According to a new study in the journal Biological Psychiatry, the brains of girls with autism rarely differ in size from those of girls that lack the condition, while boys whose brains do not normalize in size as they age tend to exhibit the most acute mental disabilities.

Meanwhile, a separate but related study in the same journal reveals that the rate at which white matter develops in certain brain regions has a direct impact on the severity of ASD in both boys and girls.

The brains of all children undergo major changes during the early years of life. In particular, the proportion of gray matter – which contains neuronal cell bodies – tends to decrease, while white matter – which is made up of the branches that connect neurons together – increases. However, previous research has indicated that this development occurs at an abnormal rate in children with ASD.

For instance, it has been noted that children with autism under the age of 3 tend to suffer from disproportionate megalencephaly (DM), whereby the size of their brain is unusually large in relation to their height. However, studies have indicated this tends to normalize during late childhood, leading to improvements in cognitive function.

To investigate whether or not this truly is the case, the study authors used magnetic resonance imaging (MRI) to scans the brains of 294 children with autism and 135 children without autism. Each child was scanned four times between the ages of 3 and 12, allowing the researchers to track changes in their brains during this period.

Results showed that boys with ASD tended to have larger brains than non-autistic boys throughout their childhood, largely due to an excess of gray matter. Brain size did not appear to normalize in this group, although boys whose DM did reduce tended to exhibit the greatest decreases in autistic symptoms.

Interestingly, virtually none of the girls with autism included in the study displayed DM at any point during their childhood, suggesting that enlarged brain size is unique to autistic boys. However, white matter development was found to be considerably slower in girls with ASD than non-autistic girls.

Furthermore, while the proportion of gray matter decreased in all children over time, this decline was less pronounced in both boys and girls with autism.

To conduct the second study, the same group of researchers scanned the brains of 125 children with autism and 69 non-autistic children at numerous time points between the ages of 2.5 and 7 years. The data revealed that the rate at which white matter develops in five key brain regions tends to correlate with changes in autism severity.

Specifically, children who displayed faster white matter growth in these regions generally experienced an improvement in their condition, while slower white matter development was associated with a worsening of ASD symptoms.

The brain regions that appear to be most directly involved in this process include the corpus callosum, which has previously been linked to repetitive behaviors and social deficits, and the internal capsule, which is associated with several core symptoms of ASD.

Commenting on these results, study author Derek Sayre Andrews explained in a statement that “these studies are so important because they get us closer to a point where we can use our understanding of the underlying biology of autism to directly improve the quality of life for individuals in the autistic community.

“And that really is the ultimate goal of our research.”


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