A new study shows a surprisingly high prevalence of autism is found in patients with a condition known as agenesis of the corpus callosum. This rare disorder is suffered when connections between the left and right sides of their brain are missing.
The study, by a team of neuroscientists at Caltech, is the first to show a link between the two disorders.
In the above MRI images, a neurotypical control is shown to the left. An adult with complete agenesis of the corpus callosum is shown on the right. The corpus callosum is indicated in red, fading as the fibers enter the hemispheres in order to suggest that they continue on. The anterior commissure is indicated by light aqua.
The corpus callosum is the largest connection in the human brain, connecting the left and right brain hemispheres via about 200 million fibers. In highly rare cases it is surgically cut to treat epilepsy, resulting in the famous “split-brain” syndrome.
People with agenesis of the corpus callosum (AgCC) are like split-brain patients in that they are missing their corpus callosum, except they are born this way. In spite of this considerable brain malformation, many of these individuals are relatively high-functioning individuals.
High Functioning Autism Spectrum
Such people have jobs and families, but tend to have difficulty interacting with other people, among other symptoms such as memory deficits and developmental delays. These difficulties in social behavior bear a strong resemblance to those faced by high-functioning people with autism spectrum disorder.
“We and others had noted this resemblance between AgCC and autism before,” said lead author Lynn Paul.
But no one had directly compared the two groups of patients. This was a challenge that the Caltech team was distinctively positioned to do. It had studied patients from both groups over the years and tested them on the same tasks.
“When we made detailed comparisons, we found that about a third of people with AgCC would meet diagnostic criteria for an autism spectrum disorder in terms of their current symptoms,” said Paul.
One significant difference between the two sets of patients did surface in the comparison. People with autism spectrum disorder showed autism-like behaviors in infancy and early childhood, but the same type of behaviors did not seem to emerge in individuals with AgCC until later in childhood or the teen years.
“Around ages 9 through 12, a normally formed corpus callosum goes through a developmental ‘growth spurt’ which contributes to rapid advances in social skills and abstract thinking during those years,” said Paul. “Because they don’t have a corpus callosum, teens with AgCC become more socially awkward at the age when social skills are most important.”
AgCC can now be diagnosed before a baby is born, using high-resolution ultrasound imaging during pregnancy, according to co-author Ralph Adolphs This latest development also opens the door for some stirring future research.
“If we can identify people with AgCC already before birth, we should be in a much better position to provide interventions like social skills training before problems arise,” Paul says. “And of course from a research perspective it would be tremendously valuable to begin studying such individuals early in life, since we still know so little both about autism and about AgCC.”