Autistic 4-and 5-year olds have larger brains than normally developing children, states researchers who feel that this difference could have started to occur at a much earlier age.
An earlier study had established that the brains of 2-year old autistic children differed from their peers'.
Study author Heather Cody Hazlett, an assistant professor in the department of psychiatry at University of North Carolina, Chapel Hill School of Medicine stated, "Our prior paper found that at age 2, children with autism had brain overgrowth, meaning their brains were larger than the comparison children. We now know this overgrowth was maintained. The children with autism kept having significantly enlarged brains at 4 and 5 years old."
This was discovered through MRIs done on 59 children aged 18 to 35 months with an autism spectrum disorder and 38 children who did not have autism. Two years later, a follow-up MRI was done on about 38 children with an autism spectrum disorder and 21 normally developing children.
Researchers examined the volume of white matter (the connective tissue of the brain), gray matter (made up of neurons), cortical thickness and brain surface area. They found autistic kids 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 researchers also discovered through a comparison of data on head circumference of children with ASD and control children that increased head size in autism starts at around age 1. Behavioral changes of children who were developing normally at 6 months are often noticed by 12 months in kids later diagnosed with autism.
Since the "brain overgrowth" at age 2 remains stable through age 4 it could only mean that the overgrowth starts even earlier in life.
Hence, further research is needed of the first year of a child's life when the differences start to become manifest. It is also yet to be studied whether the brain overgrowth seen in young children with autism coincides with or precedes the onset of symptoms.