A new study published in the journal Current Biology has identified differences in the way people with autism respond to smells, suggesting a "sniff test" could be used for early diagnosis of the condition.
Think of a pleasant smell - a bunch of flowers, for example. You would likely take a big sniff in order to inhale the floral aroma. When it comes to bad smell, however, you would restrict the airflow in your nose to avoid inhaling it.
Study author Noam Sobel, of the Weizmann Institute of Science in Israel, and colleagues found that children with autism are unable to make such adjustments - they sniff the same way regardless of whether they are presented with good or bad odors.
In the US, around 1 in 68 children have been diagnosed with autism, the majority of whom are boys. The condition is the fastest growing developmental disorder in the country.
At present, there is no medical test for autism. It is most commonly diagnosed via developmental screening, where a doctor assesses how a child moves, speaks, learns and behaves in order to determine whether there are any delays in these areas.
But Sobel and colleagues say they may have uncovered a marker for autism, paving the way for a medical test for the condition.
The team notes that past studies have suggested individuals with autism have impairments in areas of the brain responsible for sensory and motor coordination - known as "internal action models," or IAMs.
"IAMs are brain templates that allow action initiation based on sensory expectations alone and ongoing refinement of motor output based on sensory input flow," they explain. "Because the sniff response entails fine adjustment of a motor process (the sniff) in precise accordance with sensory input (the odor), it can be considered an IAM."
The researchers set out to determine whether sniff response differs in children with autism, comparing the sniff response of 18 children with the disorder with that of 18 children free of the condition.
Sniff test identified autism with 81% accuracy
The team created what they call a "computer-controlled air-dilution olfactometer equipped with a custom-designed double-barreled pediatric nasal cannula," allowing them to deliver different odors to the children while measuring their sniff response - determined by nasal airflow - at the same time.
Using this device, the researchers delivered pleasant smells (rose or shampoo) and unpleasant smells (sour milk or rotten fish) to the children over a 10-minute period and measured their sniff response.
They found that children without autism were able to adjust their sniff response within 305 milliseconds of being presented with an odor, while children with autism did not adjust their sniff response at all.
The team says that using the differences they identified in sniff response between the two groups, they were able to identify the children as being with or without an autism diagnosis with 81% accuracy.
In addition, they found that the more abnormal the sniffing response among children with autism, the more severe their social symptoms of autism were. "We propose that the altered IAM that is the sniff response leads to altered olfaction, which contributes to impaired social communication," say the authors.
While the researchers note that further studies are needed to confirm their findings, their study opens to door to a sniff test that could be useful for early autism diagnosis.
"We can identify autism and its severity with meaningful accuracy within less than 10 minutes using a test that is completely nonverbal 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. Such early diagnosis would allow for more effective intervention."
Next, the researchers hope to determine whether olfactory impairment is involved social impairments among children with autism. They also plan to find out whether people with other neurodevelopmental conditions have similar sniff-response patterns to those identified in this study.
Last month, Medical News Today reported on a study suggesting children with autism have enhanced visual search abilities from the age of 9 months - a finding that could one day lead to eye-tracking technology for early diagnosis.