The brains of children with autism are up to 10% bigger than other children’s by the time they are 2 years old, researchers at the University of North Carolina at Chapel reported in the journal Archives of Psychiatry. The faster brain growth seems to happen when the baby is about one year old. The extra growth occurs because of more folding on the surface of the brain, the authors explain.
The researchers also found that those with a larger brain at the age of 2 years also had larger brains by the time they were four or five – however, it was the same degree of growth as when they were two years old. This extra brain growth did not continue after the age of two. The changes identified when they were two were caused by extra growth that had occurred beforehand.
They also found that the enlargement of the outer part of the brain (cortical enlargement) was linked to more folding on the brain’s surface – it had a larger surface area – and not because there was more gray matter, the outer layer was not thicker.
Heather Cody Hazlett, PhD., said:
“Brain enlargement resulting from increased folding on the surface of the brain is most likely genetic in origin and a result of an increase in the proliferation of neurons in the developing brain.”
In two studies, one in 2005 and the other one recently, Hazlett and team looked at MRI (magnetic resonance imaging) scans of kids’ brains using software developed by Martin Styner, PhD, who now works at the University of Utah.
Joseph Piven, MD., said:
“From earlier work by our group on head circumference or head size in children with autism, we think that brain overgrowth in many children with autism may actually be happening around the first birthday. Together these findings suggest that we should be searching for genes that may underlie the over-proliferation of neurons in this early post-natal period.”
Two studies are underway at the University of North Carolina which are looking into what link there might be between autism, brain growth and genetic factors.
Hazlett said:
“It was important to continue to follow these children to track their brain development to see if the brain and behavioral differences we observed were maintained as the children matured.”
The researchers are also involved in IBIS (Infant Brain Imaging Study), focusing on children who have an older sibling with autism.
Piven said:
“We are studying infant children at high genetic risk for autism, by virtue of their having an older brother or sister with autism somewhere around 20 percent of those children will develop autism. We are doing brain scans and behavior assessments on those children at 6, 12 and 24 months of age to look at how the brain develops in the subgroup that develop autism before they have symptoms of autism at 6 months of age and over the interval that they develop autism – between 6 and 24 months of age, in most cases. We are also looking at whether specific gene alterations may be responsible.”
No typical medical test that identifies autism currently exists. It is usually diagnosed when the child is about 3 years old, and is based on developmental and behavioral signs. However, subtle signs are usually present earlier on.
Heather Cody Hazlett, PhD; Michele D. Poe, PhD; Guido Gerig, PhD; Martin Styner, PhD; Chad Chappell, MA; Rachel Gimpel Smith, BA; Clement Vachet, MS; Joseph Piven, MD
Arch Gen Psychiatry. 2011;68(5):467-476. doi:10.1001/archgenpsychiatry.2011.39
Written by Christian Nordqvist