Science has long realized that autism isn't a figment of interpretation, but has a genetic background. Now a study claims to show certain gender differences in brain structure between autistic male and female toddlers.
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Autism, in its various forms, is far more common in males than females, though how much so is unclear – some say two times as many boys as girls, some say five times as many. Either way, why this is so remains unknown.
Meanwhile, studies on young children aged 3 to 5 found that differences between boys and girls in a certain brain structure: the corpus callosum, the largest bundle of white-matter nervous tissue in the brain, which connects the "left brain" to the "right brain." The study at the MIND Institute of the University of California was published today in Molecular Autism.
The research encompassed 139 autistic children aged 3 to 5. Of them, 112 were boys and the rest girls. Their brain structures were compared with a control group of 82 "typically developing" children (two-thirds male, a third female). The pattern of nerve fibers projecting from their little corpus callosi were scanned with MRI.
Now, there are subtle structural gender differences in the corpus callosum among all men/women. In autistic children, there are even more differences – and these differences themselves turn out to be different in boys and girls.
In both sexes, the regions of the corpus callosum connected to the frontal lobe differed between the autistic children and the control children.
Girls with autism had bigger callosal regions connecting to the cortex part involved in emotional processing and reward-related decision-making.
Boys with autism had bigger callosal regions connecting to the region involved in higher order "executive function," such as planning.
However, Dr. Ilan Dinstein of the departments of Psychology, and Brain and Cognitive Sciences at the Ben-Gurion University of the Negev, cautions against blithely assuming that a scan of the brain can (in the future) tell whether a toddler may have autism.
If one takes the group of the test subjects, one finds a very wide range; in other words, the differences between the autistic group and control group is quite small compared with the differences between each group, he pointed out to Haaretz. The two groups also overlap.
Even so, the scientists' recommendation is that males and females with autism should be evaluated separately. Another implication is that these differences in brain structure develop early, before three years of age, the scientists say.
It bears putting this study into the context of a vast meta-study that found no differences in structure between autistic brains and 'typical' brains.
Dinstein, who led that paper, notes that the meta-study related only to males, aged six to 35. Other research done on children from about age two and a half to 10 – in other words, significantly younger – may be indicative of some structural differences, he says.
This latest study used a scanning method that examined the corpus callosum, which is part of the white matter in the brain – the "information conduits" that connect the brain's various parts. More than one study has now found, he points out, that there are differences between autistic children and control children in that white matter, though what the difference is seems less clear. The meta-study looked at other aspects of the brain, not the interconnecting tissues, so at that level too, they do not contradict each other, Dinstein explains.
"I and others hope that dimensions are found that can distinguish between groups with and without autism, especially at very young ages of a year to 3," Dinstein told Haaretz. "There is a hope that at the start of the story, the differences are more significant." But the state of the art clearly isn't there yet.