Study: Siblings of Autistic Kids Show Similar Brain Activity

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Victoria Yee

The genetic roots of autism may reach further in families than previously thought, according to new research.

In a study published in the journal Translational Psychiatry, scientists at the University of Cambridge report that even the unaffected siblings of autistic children show signs of brain differences that set them apart from children in non-autistic families.

The researchers, led by child psychiatrist Dr. Michael Spencer, studied the brain activity of 120 youngsters as they viewed pictures of human faces making different expressions. Forty of the children were diagnosed with an autism spectrum disorder, ranging from Asperger’s to autism; another group of 40 comprised the autistic children’s unaffected siblings; the final group were children from families with no autistic members.

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While the children looked at the pictures, Spencer’s team scanned their brains using functional magnetic resonance imaging (fMRI), which measures activity in real time in different parts of the brain. The team used the activity patterns of children from families not affected by autism as the standard: when these youngsters saw pictures of happy faces, 11 regions in the brain connected to social processing and emotions became more active. When the autistic children saw the same pictures, these areas did not light up to register the happy faces.

That finding wasn’t so surprising — it’s been known that autistic youngsters have difficulty learning and reading social cues, which include the emotional signals that people send out through their facial expressions, body language and the tone of their voice. What was more unexpected was that the unaffected siblings of the autistic children showed similar reduced activity in these areas. In fact, says Spencer, their brain activity patterns looked very much like those of their autistic siblings, and less like those of normal controls, even though they were not affected by autism.

“We were struck by how similar the activity was in unaffected brothers and sisters compared to their sibling with autism,” he says. “Which seems to suggest that this is a shared pattern of activity due to inherited genes that may make family members at increased risk of autism.”

The fact that autism has genetic roots has been well established by studies finding that the siblings of children with autism are 20 times more likely to develop autism as well, compared with those who don’t have the developmental disorder in their family. But because these siblings don’t exhibit any signs of autism, it’s never been known exactly which genes drive the disorder or how.

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It’s also a challenge to tease apart how much genetic factors versus environmental factors contribute to autism. “Comparing unaffected siblings to controls [who don't have autism in the family] and finding the differences between those two groups has long been the Holy Grail of autism research,” says Spencer. “Because any differences between them must relate to the family history of autism, and therefore to the inherited genes for autism.”

The results will likely not have an immediate effect on diagnosing or treating autism in the clinic, say experts, but instead will improve researchers’ understanding of what triggers the developmental disorder. Focusing on the brain centers that process social cues, for example, may lead to better therapies designed to address whatever deficits are causing autistic children to have impaired activity in this part of their brain.

That’s not to say there won’t be demand for turning these results into some type of test for autism, particularly for worried parents-to-be who might be concerned about autism risk in their families. Screening for reduced activity in social-processing areas of the brain could help parents predict whether or not they are likely to have children affected by autism.

But before that can happen, says Spencer, more work needs to be done to isolate the other factors that are driving the disorder. The reduced brain activity that his study uncovered is only one of potentially many such factors that scientists need to understand better before they can offer any type of screening for autism to parents.

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Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME‘s Facebook page and on Twitter at @TIME.