Why does the sound of chewing annoy us?

Squelching may be the best way to describe it—that squishy, smack-like noise that some people make while chewing food. This sound has a way of hijacking your attention so that it becomes the center of your every thought. Of course, not everyone will experience this. But for some, the sound of people chewing evokes a visceral response. So why would this affect some people more than others? There are many possible explanations, including one from our DNA and the TENM2 gene.

Misophonia is a condition where people develop a strong aversion to specific sounds, usually responding with increased anxiety or anger. Though the sound of someone chewing is a commonly discussed trigger sound, the exact noises that people become averse to varies from case to case. This is an important observation because it suggests that misophonia development is likely influenced by individual differences—both environmental and potentially genetic differences1.

Initial descriptions of misophonia suggested that people are born with a predisposition to hearing and noticing specific patterns1. With a heightened awareness of patterned sounds—like those produced by someone chewing or clicking a pen—it’s possible that predisposed individuals will eventually hear these noises in a situation that provokes an emotional response, like the feeling of being annoyed. Researchers suggested that this initial annoyance could lead to increased focus on the triggering sound and initiation of a repeating cycle of awareness, annoyance, and increased awareness. As the cycle continues, the misophonic aversion develops.

 

 

So what would cause a person to be predisposed to such a cycle? One possible answer came in 2014 when researchers performing a large scale genetic study found that a variant—or change in the DNA sequence—was more commonly found in people who reported feeling enraged by the sound of chewing2. This variant wasn’t located in a specific gene, but it could impact genes in the surrounding area, which includes TENM2.

A genetic explanation for why people may be predisposed to misophonia is not entirely new—previous observations had noted that this condition tended to run in families which indicated a potential genetic link1,3. But the identification of a variant near TENM2 was the first time someone had found a specific DNA sequence linked to this condition.

TENM2 is a gene that codes for the teneurin-m2 protein in humans4. This protein sits at the surface of cells where it can help different cells communicate with each other. Relevant to misophonia, teneurin-m proteins are largely found in our brain where they play a role in neuron growth and formation of neural networks4. Scientists studying misophonia have suggested that people with this condition may have some sort of neural change that results in increased awareness of patterned noises, or increased association of emotion with external stimuli1. It’s possible then that changes in the TENM2 gene could result in altered neuronal patterning, and a predisposition to misophonia.

 

Research is still in its early stages

It’s important to note that there is very little known about misophonia and what causes it. More work is needed to directly establish the hypothetical effect of the misophonia-linked variant on the TENM2 gene’s function, or its effect on neuronal patterning—and to confirm that it’s indeed connected to misophonia. All of this means that research on TENM2 and misophonia is still in its early stages, but these findings provide researchers with interesting pathways forward. Future studies will likely look to see why TENM2 may be linked with misophonia, and will aim to identify other changes in the DNA that may also affect a person’s predisposition to the condition.

While we can’t explain why the association is there, we can test to see if someone has inherited this misophonia-linked variant. People who want to explore their DNA in a fun and creative way can do so with Dot One’s Personalized Scarf—a scarf with color design based on your DNA. Along with the scarf, you receive a booklet that details more than 30 traits you can learn about from your DNA, including whether you’ve got a variant near TENM2 that’s associated with misophonia. So if you’re ready to explore your DNA in a tactile way, check it out here.

 

1Brout, Jennifer J. et al. “Investigating Misophonia: A Review of the Empirical Literature, Clinical Implications, and a Research Agenda.” Frontiers in Neuroscience 12 (2018): 36. PMC. Web. 25 Sept. 2018.

2Fayzullina, Saniya, et al. “White Paper 23‐08 Genetic Associations with Traits in 23andMe Customers.” White Paper 23‐08 Genetic Associations with Traits in 23andMe Customers, 23&Me, 4 Dec. 2014, objects.23andme.com/res/pdf/eEK9zpYQRGYVvUXuEd0VQw_23-08_Genetic_Associations_With_Traits.pdf.

3Sanchez, Tanit Ganz, and Fúlvia Eduarda Da Silva. “Familial Misophonia or Selective Sound Sensitivity Syndrome: Evidence for Autosomal Dominant Inheritance?” Brazilian Journal of Otorhinolaryngology, 2017, doi:10.1016/j.bjorl.2017.06.014.

4Young, Timothy R., and Catherine A. Leamey. “Teneurins: Important Regulators of Neural Circuitry.” The International Journal of Biochemistry & Cell Biology, vol. 41, no. 5, 2009, pp. 990–993., doi:10.1016/j.biocel.2008.06.014.

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