Autistic boys far outnumber their female counterparts, by a widely cited male:female ratio of 4 to 5:1, but researchers have yet to pinpoint why autism is as much as three times more common in males.
Research published today in the journal Molecular Autism contributes to a growing body of knowledge about how autism manifests differently in boys than it does in girls. The work reveals striking differences in the way the brains of autistic boys and girls are wired.
"Differences in underlying biology, which is what we've found, suggests that there could be different underlying causes of autism in boys and in girls," lead study author Christine Wu Nordahl of The MIND Institute at the University of California at Davis said in an interview. "This could lead to more appropriate treatments."
Using magnetic resonance imaging (MRI), the researchers examined the brains of 139 preschool-aged boys and girls with autism and compared them with each other as well as with the brains of 82 normally developing children. In particular, they examined the corpus callosum, the largest nerve fiber bundle in the brain. The nerve fibers within this bundle connect the left hemisphere of the brain to corresponding regions in the right hemisphere.
This region was of particular interest partially because of its size but also because "there's a prevailing theory in autism research that one of the hallmarks of an autistic brain is disruptions in connectivity," says Nordahl.
Little is known about the differences between the brains of girls and boys with autism. According to Nordahl, this is one of the largest studies ever to use MRI scans to look at differences between autistic brains.
The scans showed that boys tend to have reduced connectivity in the orbital frontal cortex, which is involved in social behavior, whereas girls have reduced connectivity in the anterior frontal cortex, which plays a role in goal-directed behavior and other higher-order cognitive functions.
"Boys and girls are diagnosed with the same criteria but there are some subtle behavioral differences between them," Nordahl says. "We think that there are also likely differences in how their brains are organized, and this finding is an example of that."
The journal article can be found here.
