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Brains of autistic children larger at age 4, 5

The brains of 4- and 5-year-old children with autism are larger than the brains of normally developing children, and the difference probably occurs several years earlier.

Brains of autistic children larger at age 4, 5

The brains of 4- and 5-year-old children with autism are larger than the brains of normally developing children, and the difference probably occurs several years earlier.

Autism is a neuro-developmental disorder marked by social and communication impairment.

Prior research has found that at age 2, children with autism had brain overgrowth, meaning their brains were larger than those of normal children, on average being 9 percent larger.

Researchers from America did MRIs on 59 children aged 18 to 35 months with an autism spectrum disorder (ASD) and 38 children who did not have autism. Two years later, about 38 children with an autism spectrum disorder and 21 typically developing children returned for a follow-up MRI. Researchers were interested in volume of white matter (the connective tissue of the brain), gray matter (made up of neurons), cortical thickness and brain surface area. At age 2, autistic children had a larger total brain volume than non-autistic children. Two years later, researchers were able to measure cortical thickness and brain surface area, in addition to volume. They found that autistic children had larger brain volume and greater brain surface area, though they did not show a difference in cortical thickness. The rate of brain growth was about the same in children with and without autism.

The findings suggest that the brain overgrowth is occurring prior to age 2, and perhaps prior to age 1. Data on head circumference of children with ASD compared with control children suggests that increased head size in autism starts at around age 1. Behavioural changes of children who are developing normally at 6 months are often noticed by 12 months in children later diagnosed with autism. Prior research has linked greater brain surface area to genes that promote the proliferation of neurons. What we know is that the mechanism for the folding of the brain is genetic in origin, resulting from an increase in the proliferation of neurons.

However, understanding that the brain overgrowth at age 2 remains stable through age 4 - meaning that it doesn't become more pronounced, nor does other child's brain size catch up - does suggest that researchers should start looking even earlier in life to see when the brain overgrowth begins. It does encourage researchers to more closely evaluate brain development in the months just before and after a child's first birthday, since this is when early signs of autism often manifest initially and when changes in head size also become evident.
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