The way children sniff different aromas could form the basis of a test to accurately detect autism, a new study has found.
Researchers have found that autistic children go right on sniffing in the same way, no matter how pleasant or awful the scent is.
The findings suggest that non-verbal tests related to smell might serve as useful early indicators of autism spectrum disorder (ASD), the researchers said.
"The difference in sniffing pattern between the typically developing children and children with autism was simply overwhelming," said Noam Sobel of the Weizmann Institute of Science in Israel.
Earlier evidence had indicated that people with autism have impairments in "internal action models," the brain templates we rely on to seamlessly coordinate our senses and actions.
It wasn't clear if this impairment would show up in a test of the sniff response, however.
To find out, Sobel, along with Liron Rozenkrantz and their colleagues, presented 18 children with ASD and 18 normally developing children (17 boys and 1 girl in each group) with pleasant and unpleasant odours and measured their sniff responses.
The average age of children in the study was 7. While typical children adjusted their sniffing within 305 milliseconds of smelling an odour, the researchers said, children on the autism spectrum showed no such response.
That difference in sniff response between the two groups of kids was enough to correctly classify them as children with or without a diagnosis of ASD 81 per cent of the time.
Moreover, the researchers said that increasingly aberrant sniffing was associated with increasingly severe autism symptoms, based on social but not motor impairments.
The findings suggest that a sniff test could be quite useful in the clinic, although the researchers emphasise that their test is in no way ready for that yet.
"We can identify autism and its severity with meaningful accuracy within less than 10 minutes using a test that is completely non-verbal and entails no task to follow," Sobel said.
"This raises the hope that these findings could form the base for development of a diagnostic tool that can be applied very early on, such as in toddlers only a few months old. Such early diagnosis would allow for more effective intervention," said Sobel.
Researchers now plan to test whether the sniff-response pattern they have observed is specific to autism or whether it might show up also in people with other neurodevelopmental conditions.
The study was published in the journal Current Biology.