Smell test ‘offers early diagnosis 
of autism’

Children with autism are slower to respond to changes between nice an unpleasant smells. Picture: Getty
Children with autism are slower to respond to changes between nice an unpleasant smells. Picture: Getty
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Testing a child’s reaction to smells may provide an effective new way of diagnosing autism at young ages, research has shown.

People with autism fail to adjust their “sniff response” in the normal way when switching from nice to nasty odours.

For instance, the sweet scent of a rose usually prompts a deep intake of breath, whereas a visit to a gents toilet is likely to have the opposite effect.

But such an ability to co-ordinate senses and actions is impaired in those suffering from autism spectrum disorders (ASDs).

Since the test doesn’t require a verbal task, it could one day help doctors diagnose autism in very young children, permitting interventions to begin at a younger age.

The researchers presented 18 children with ASD and the same number of normally developing children with pleasant and unpleasant smells, and measured their sniff responses.

Typical healthy children adjusted their sniffing within 305 milliseconds of smelling an odour, but this was not the case for those with autism.

The difference in sniff response was large enough to allow the researchers to spot the autistic children with 81 per cent accuracy.

Increasingly aberrant sniffing was also associated with increasingly severe autistic symptoms, the scientists reported in the journal Current Biology.

Lead researcher Dr Noam Sobel, from the Weizmann Institute of Science in Israel, said: “The difference in sniffing pattern between the typically developing children and children with autism was simply overwhelming.

“We can identify autism and its severity with meaningful accuracy within less than ten minutes using a test that is completely non-verbal and entails no task to follow. 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.”

This was however a small, early study, so the sniff test will have to undergo more extensive trials before it can be ready for clinical use.

The researchers now plan to test whether the sniff-response pattern they’ve observed is specific to autism or whether it might show up also in people with other neurodevelopmental conditions. They also want to find out how early in life such a test might be used.