Autism spectrum disorder probably isn't all in the brain, according to a new study.
New research at Harvard Medical School in the US has found links between the condition (ASD) and genetic defects in the body's nervous system.
"An underlying assumption has been that ASD is solely a disease of the brain, but we've found that may not always be the case," says neurobiology professor David Ginty, who led the research.
By engineering mice with perfectly normal brains but genetic defects in the nerves in their limbs and toes, the researchers were able to generate ASD-like behaviour.
Mice with the neural defects showed heightened anxiety when confronted with mice they'd never seen before, and interacted less -- typical ASD traits. They also showed heightened sensitivity to touch stimuli.
"How closely these behaviours mimic anxiety seen in ASD in humans is up for debate," Prof Ginty says, "but in our field, these are well-established measures of what we consider to be anxiety-like behaviour and social interaction deficits."
The genes had previously been linked to ASD, but it was assumed they were affecting how the brain functions.
It is not yet known why a heightened sensitivity to touch in the limbs and toes would lead mice to withdraw and show signs of anxiety, but the researchers suspect it is because they suffer from sensory overload.
"We think mice with these ASD-associated gene mutations have a major defect in the 'volume switch' in their peripheral sensory neurons," says contributing author Lauren Orefice.
"Essentially, the volume is turned up all the way so the animals feel touch at an exaggerated, heightened level".
"We think it works the same way in humans with ASD," says Prof Ginty.
The underlying cause of ASD, if it has one, is still unknown. It is not vaccines.
"An abnormal sense of touch is only one aspect of ASD, and while we don't claim this explains all the pathologies seen in people, defects in touch processing may help to explain some of the behaviours observed in patients with ASD."
They hope the discovery will lead to research into potential ways to bring the "volume" down, whether through drugs or at the genetic level.