Autism or Not: The Clue is in the Senses

Reference: Osório, J.M.A., Rodríguez-Herreros, B., Romascano, D. et al. (2021). Touch and olfaction/taste differentiate children carrying a 16p11.2 deletion from children with ASD. Molecular Autism 12, 8.  

Imagine that you are cooking beef stew, and the stove gives off a little bit of smoke. The fire alarm goes off. You cover your ears to soften the noise as you fan away the smoke until it finally quiets. Such an experience is a common one, and enough to hurt anyone’s ears. However, what if the noise were even louder? What if your meal that day tasted even sharper? What if it irked you? There are baselines that most people experience with their senses. For instance, everyone with an average level of hearing hears a fire alarm as loud, but some experience it as piercingly loud. Such people may have auditory sensitivities. Sensory sensitivities are heightened experiences of senses. While auditory sensitivities are one example of sensory sensitivities, people may have heightened sensitivity in any other senses, such as sight or taste. These impact how strongly people experience the world around them.

Sensory sensitivities are part of the experience of many individuals with autism spectrum disorder and other neurodevelopmental conditions. These symptoms became a particular topic of focus for researchers after the revised Diagnostic Statistical Manual (DSM-5) – a guide used to aid in the diagnoses of mental illnesses, neurodevelopmental disabilities, and more – was published, and sensory symptoms were included under autism spectrum disorder’s criteria. Sensory processes serve an adaptive function in that they help others navigate and make sense of the world. If there is an impairment, dysfunction, or merely an undetected difference in experience that is not understood, it can have a long-term impact for one’s developmental course; early intervention is key so that parents and children can understand the children’s sensory impairment and accommodate properly so that it becomes easier to function as adults1.  

When faced with a sensory stimulus, an individual may appear to under-respond (hypo-responsiveness), over-respond (hyper-responsiveness), or seek out the stimulus with a heightened sense of fascination (seeking). Someone who exhibits hypo-responsiveness may consume hot chocolate and not taste it as strongly as others, so they might not care for it. People who are hyper-responsive in the same scenario may experience the taste too strongly and avoid drinking it again later, and people who seek the sense of taste may find that an aspect of the taste (i.e., the sweetness, the richness) stands out to them and want to consume it more. 

Previous studies have found that any of these three responses may often co-occur with autism spectrum disorder and other neurodevelopmental disorders. Usually, these studies receive information as reported by caregivers on specialized questionnaires, testing observational sensory symptoms, balance/motion, social participation, ability for planning and ideas, and body awareness. While this is an excellent way to record the behavior’s progress over time, it is difficult to learn about how sensory sensitivities affect the people who have them, as well as other information that only the people who experience them may know. Hence, researchers may perform a lab experiment to observe how people with sensory sensitivities behave under circumstances in which they are exposed to something that they may respond to due to their sensory sensitivities. 

Other studies seek to understand the physiological reason behind our reactions to sensory stimuli. For instance, the deletion of a DNA segment at the 16p11.2 locus, found on an arm of chromosome 16, is often associated with autism spectrum disorder. Studies on mice have found that the same deletion may be associated with sensory differences in mice, which led researchers to wonder if the same were true for humans. From there, researchers aim to learn the extent to which the DNA segment deletion and sensory sensitivities related to autism are linked. After all, not everyone who has a set of sensory sensitivities is autistic and not everyone who is autistic experiences a sensory sensitivity.

A study by Joana Osorio and colleagues sought to gain more insight into sensory sensitivities by examining the sensory processes of 121 autistic children (as diagnosed based on a clinical phenotype), 17 16p11.2 deletion carriers (as determined by genetic testing), and 45 neurotypical children (i.e., children without a neurodevelopmental disability), all 2-12 years old. Their parents filled out a specialized questionnaire, which included questions that would pick up on hypo-responsiveness, hyper-responsiveness, and seeking. Then, laboratory-based tactile discrimination tasks (games in which participants were asked to distinguish different textures) were carried out to observe the differences among the three participants groups. Any defensiveness (or lack thereof) was noted, as some participants would exhibit hyper-responsiveness in that they would experience more adverse reactions than others. Children were also given intelligence tests to measure their cognitive abilities, and an autism diagnosis assessment. Both assessments served to provide more information about possible diagnoses that may further explain the participants’ responses to stimuli.

Through the questionnaires, the researchers found that while 16p11.2 deletion carriers had more sensory impairment across all senses than neurotypical children, autistic children had more tactile, olfactory, and taste sensitivities than 16p11.2 deletion carriers. Such sensory sensitivities may differentiate autistic children from 16p11.2 deletion carriers. However, in the laboratory-based task, 16p11.2 deletion carriers appeared to have more tactile sensitivities. The researchers hypothesize that this difference reflects the possibility that the parent report questionnaires did not encompass all possible tactile sensitivity responses a child could have, because it only asked about defensiveness.  A larger sample size is needed to come to any more concrete conclusions. 

While both groups of participants had increased sensory sensitivities compared to neurotypical groups, autistic participants were more likely to have increased sensitivities in touch, smell, and touch than their 16p11.2 deletion participant counterparts. Neither group differed from one another in their responses to sensory stimuli. It’s important to note that some ASD participants are 16p11.2 carriers.

There was no difference between 16p11.2 deletion carriers and autistic children in whether or not they responded with hyper-responsiveness, hypo-responsiveness, or seeking. As a result, it is harder to distinguish sensory sensitivities caused by autism or the 16p11.2 deletion without additional studies about specific responses, but the senses of touch, smell, and taste stand out as more common in one group than the other. A potential future direction in sensory sensitivity research may involve performing the same study on a larger sample size to continue to examine the relationship between sensory sensitivities, autism, and 16p11.2 deletion carriers. 

Additional References

1. Tomchek, Scott D., and Winnie Dunn. “Sensory processing in children with and without autism: a comparative study using the short sensory profile.” The American journal of occupational therapy 61.2 (2007): 190-200.

2. Cover Image (1): Wirchin, Jason. Five Senses. Accessed 21 September 2022 at Your Brain and Five Senses: The Science Behind Falling in Love (