When most people come across a pleasant scent, such as a nice perfume or freshly baked cookies, they typically take a good long sniff. While walking next to a dumpster, however, a person would most likely shorten his incoming breaths, minimizing the intake of the unpleasant odor.
Now, researchers have discovered that people with autism spectrum disorder (ASD) don’t make this natural adjustment like other people do. In fact, children with autism continue right on sniffing in the same way, no matter how pleasant or awful the scent.
The findings suggest that tests related to smell might serve as useful early indicators of ASD, say the researchers.
“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.
Earlier studies have indicated that people with autism have impairments in “internal action models,” the brain templates we depend on to seamlessly coordinate our five senses with our actions. It wasn’t clear if this deficit 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 typically developing children (17 boys and one girl in each group) with pleasant and unpleasant odors and measured their sniff responses. The average age of the participants was seven years old.
While typical children adjusted their sniffing within 305 milliseconds of smelling an odor, the researchers report, children on the autism spectrum showed no such response.
That difference in sniff response time between the two groups of kids was enough to correctly classify them as children with or without a diagnosis of ASD 81 percent of the time. Furthermore, the researchers report that increasingly abnormal sniffing was linked to increasingly more severe autism symptoms, based on social but not motor impairments.
The study results suggest that a sniff test could be quite useful in the clinic, although the researchers emphasize 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 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.”
The researchers plan on testing whether the sniff-response pattern they’ve observed is specific to autism or if it also shows up people with other neurodevelopmental disorders. They also want to investigate how early in life such a test could be used. But the most immediate question for Sobel is “whether an olfactory impairment is at the heart of the social impairment in autism.”
The findings are published in the Cell Press journal Current Biology.
Source: Current Biology