A new imaging study of preschoolers has seemingly identified gender differences in the way autism may manifest itself in the brain.
"This research adds to a growing body of evidence that there are differences between boys and girls with autism," said study lead author Christine Wu Nordahl.
"This is not surprising given that there are so many more males with autism than females," said Nordahl, an assistant professor in the department of psychiatry and behavioral sciences at the University of California, Davis MIND Institute.
At issue is the anatomy of the brain's largest fiber bundle structure, the corpus callosum, which connects the brain's two hemispheres.
Investigators studying nearly 140 young children with an autism spectrum disorder found that while all autism patients have fiber bundles that differ from brains of typical people, the nature of those differences change by gender.
Compared to girls with the neurobehavioral disorder, boys with autism were seen to have smaller callosal regions linking up to the part of the brain that regulates emotions and decision-making (the orbitofrontal cortex). By contrast, girls with autism were seen to have smaller callosal regions linking up with the brain region that controls planning and executing tasks (the anterior frontal cortex).
Identifying and understanding these biological differences may eventually improve how autism is diagnosed and treated in boys and girls, Nordahl noted.
"We don't yet know enough about females with autism because most research studies do not have equal numbers of females and males with autism in their samples," Nordahl said.
The U.S. Centers for Disease Control and Prevention estimates that autism spectrum disorders -- which affect about one in 68 American children -- is almost five times more common among boys than girls.
For this study, researchers used MRI scans to examine the brain structures of 112 boys and 27 girls with autism and 53 boys and 29 girls without autism. All were between 3 and 5 years old. The researchers were particularly interested in the way that nerve fibers projected from the corpus callosum to other areas of the brain.
Nordahl acknowledged the sample size was "limited." She said more research is needed, along with a larger study population of girls.
Nevertheless, Andrea Roberts, a research associate at Harvard School of Public Health, described the current findings as "interesting, specific and concrete."
"Researchers have known for a long time that there are big sex differences in the prevalence of autism, and there have been many ideas of why that might be," she noted. "So far, research hasn't really backed up any of them, but there's got to be something going on biologically to explain that."
This study shows actual physical differences in the brain between boys and girls with autism, Roberts said. "At the same time, when we look at causes and possible causes for autism, we don't find many gender differences. So clearly there are some shared things going on with boys and girls as well," she added.
The study findings appear online in the May 12 issue of the journal Molecular Differences.
Another study published in the same issue explored the notion of a "female protective effect," which suggests the female brain is somehow protected from developing autism.
In that study, researchers from Yale School of Medicine, Washington University in St. Louis and University of California, San Francisco, analyzed genes of 4,500 families affected by autism. The scientists concluded that if such protection exists, it does not appear to source back to any one specific protective gene.