Children with autism spectrum disorder do not react as well to pleasant or foul smells compared to non-ASD children. Previously, autistic toddlers were found to have a dampened response to sight, sound and touch. For their study, the researchers at the Weizmann Institute of Science in Israel used a novel technique to gauge the smell response in both ASD and control groups, with 81% accuracy. The test is unobtrusive and doesn’t require a personal account from behalf of the children – something that can be difficult to do with autistic children, who more often than not are highly uncommunicative. If the test can survive the test of time and other trials, it could very well be used to diagnose autism.

autism sniff test

Image: Greenmylife

Our respiration constantly shifts to accommodate the various smells we come in contact with. If you sense a pleasant aroma, you will likely breath in more. If you sense a stench, though, you’ll adjust to “low-magnitude sniffs” to lower your response to the awful stimulus. To measure how autistic children differ in this kind of response, the researchers used a specifically designed contraption called the olfactometer. The device delivers scents through a small tube that fits in the nostril, while a second tube measures how much air the children were breathing for each round of scent. In other words, the device measures how much time they spent smelling or much of a sniff they inhaled.

For the experiment, 36 children were selected: 18 diagnosed with ASD and 18 non-ASD children which acted as the control group. The scents were altered between pleasant smells, such as roses or shampoo, and unpleasant smells, such as sour milk or rotten fish. The control group adjusted their response according to the scent, taking a longer sniff for roses and a shorter one for rotten fish. This shift happened very quickly, within one third of second after being exposed to a new smell. The autistic children typically didn’t change their breathing, though.

“The difference in sniffing pattern between the typically developing children and children with autism was simply overwhelming,” says Noam Sobel of the Weizmann Institute of Science in Israel.

autism test

Image: Current Biology

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It’s not clear though whether the children actually have a dampened sense of smell or it has more to do with their response: internal action models (IAM).

The study says: “We do not hypothesise that children with ASD will be unable to sniff, but rather that they will generate an inappropriate sniff given a particular odour.”

The results might also explain why so many autistic children have trouble eating.

“It could be muscular problems, with swallowing and chewing, but smell is a big part of taste and children with autism may not perceive smell in the same way as other children,”  Dr. Paul Wang, senior vice president and head of medical research for Autism Speaks.

The olfactometer test correctly identified 12 of the 18 children who had autism, and 17 of the 18 control children who did not have autism.

“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 says.

“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.”

While the test could work well for children with developmental problems, it might not be that accurate in the field. Specifically, this kind of limited response might not be unique to autism spectrum disorder. Right now, the main mode of diagnosing autism is behavioral. Either the children are doing things that typical children don’t do, or they are not doing things that typical children are doing.

The fact that the test is very simple to take and doesn’t require any kind of involvement from the part of the children (the participants were sited while watching cartoons), makes it a promising tool, though. For it to be really effective, it should prove accurate for younger children. The average age of the participants was 7, but previous work shows that marking improvements can be seen if ASD children are given behavioral therapy before the age of 4. This could prove challenging to implement. First, a new study should be made with younger children, then these children should be followed as they mature to see if they actually developed ASD.