Relatives of people with autism may display autistic brain differences and behaviours despite not having the condition themselves, a study shows.
'Autistic' brain changes may be seen in the relatives of those with autism
New Scientist says the work could make it easier to spot families at risk of having an autistic child.
It could also help in the quest to find genetic and environmental triggers for the condition, experts hope.
Autism is a disorder that makes it hard for the individual to relate socially and emotionally to others.
It affects about five in 10,000 people, predominantly boys and men, and is often also associated with learning disabilities.
The New Scientist piece reported on work presented at the annual meeting of the Society of Neuroscience that took place in Washington DC this month.
Dr Eric Peterson, from the University of Colorado in Denver, spoke about his work comparing the brain scans of 40 parents with autistic children with those of 40 matched parents whose children did not have autism.
The parents of autistic children shared several differences in brain structure with their offspring, including an unexpected increase in the size of brain areas linked to movement planning and imitation - the motor cortex and basal ganglia.
However, a neighbouring brain area called the somatosensory cortex was smaller than average.
This region is important for understanding social information such as facial expressions - a skill autistic people often lack.
The cerebellum, which is important for co-ordinating movement, and a frontal region thought to play a key role in understanding the intentions of others were also smaller than average.
Another US study, led by Brendon Nacewicz from the University of Wisconsin-Madison Medical School, showed that the amygdala, a brain region involved in processing emotions, was shrunken in both autistic children and their brothers.
The brothers also avoided eye contact - a common feature of autism - just as strongly as their affected siblings, even though they did not have autism themselves.
Other researchers have been attempting to identify genes predisposing people to autism, which are thought to be as many as 20.
Professor Simon Baron-Cohen, director of the Autism Research Centre in Cambridge, in the UK, said: "First-degree relatives - parents or siblings of those with autism - may have some but not all of those genes, which would explain why they do not have autism but do show some milder manifestations.
"We have known for years that family members of people with autism may share some traits.
"However, the finding that there are differences in brain structure in parents of children with autism compared to parents of children without autism is new.
"It is telling us that these genes, as they run through families, are affecting brain function and structure not just in the person with autism but also in their first degree relatives."
He said it was too early to use these brain changes to spot people who might be at risk of autism, but he added: "I'm sure that will come."