Brain deficits found in relatives of autism sufferers
Unaffected family members show characteristic abnormalities.
People can have physical brain abnormalities similar to those found in autistic individuals without having the disorder themselves. These results come from two studies, which were presented at a conference over the weekend. Brain scans show striking similarities between the brains of autistic patients and those of their non-autistic parents and siblings.
The results are prompting researchers to ask how some people can be unaffected by brain deficits that cause such pronounced behavioural abnormalities in others.
In one study, Eric Peterson of the University of Colorado at Boulder and his colleagues scanned the brains of 40 parents of autistic children and compared the results with functional magnetic imaging (MRI) scans from 40 controls. The data look much like those obtained for comparisons between autistic and non-autistic brains, says Peterson. The results were discussed on 13 November at the annual meeting of the Society for Neuroscience in Washington.
Some areas of the brain region known as the prefrontal cortex were smaller than normal in the parents of autistic children, for example. This part of the brain is involved in understanding other peoples' motivations, something that autistic people find difficult and is thought to lie behind the problems they face in interacting socially.
Look me in the eyes
Another typical symptom of autism is the tendency to avoid making eye contact. This behaviour was studied by Brendon Macewicz and colleagues at the University of North Carolina, Chapel Hill. He gave nine families with an autistic child and unaffected brother a digital camera and told them to take pictures of friends and family. Macewicz then mixed up the shots with images of strangers and tracked the childrens' eye movements while asking them to say whether the people they saw in the pictures were familiar or not.
Most people rely heavily on looking at the eyes when asked to complete this task. But autistic children are known to avoid the eyes and focus on other aresas of the face. To Macewicz's surprise, the non-autistic siblings did almost exactly the same.
"This piqued our curiosity," he says. The team then ran MRI scans on the brothers, focussing on the part of the brain known as the amygdala. This area is involved in fear and is typically smaller in autistic people. "It was very interesting," says Macewicz. "The children showed a similar decrease in amygdala size to their autistic siblings." The difference was around 5-10%.
The results are intriguing, say the researchers, because the parents and siblings had not been diagnosed with autism. Macewicz says it is likely that in the unaffected siblings other brain areas, perhaps in the frontal lobes, are helping to regulate the amygdala and compensate for its smaller volume.
It may be that a core set of brain abnormalities has to be present for autism to occur, adds Peterson, and that the parents he studied do not have them all. He points out that some autism-related behavioural traits have previously been seen in the relatives of people with the condition, but that these current studies are among the first to show similarities in brain anatomy.
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