Autism Behaviors May Be Related to Differences in Peripheral Nerves, Study Says

Autism is generally considered to be a disorder of the brain, but a new study shows that the peripheral nervous system may actually play a large role in the condition.

The nerves in the peripheral nervous system control our sense of touch, sensation, and pain. Now researchers believe there may be differences in these nerves in people with autism compared to people who are not on the autism spectrum.

“More than 70% of people with autism have differences in their sensory perception,” says study author Sung-Tsang Hsieh, M.D., Ph.D., of National Taiwan University Hospital in Taipei and a Fellow of the American Academy of Neurology.

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“For some people, even a light touch can feel unbearable while others may not even notice a cut on their foot. If larger studies can confirm these results, it is possible that further insight into the peripheral nervous system could help us understand how this disorder develops and potentially light the way for treating these distressing sensory symptoms that most people with autism experience.”

The study involved 32 men with an average age of 27, all of whom are on the autism spectrum. These participants were compared to 27 men and women with an average age of 33, none of which had autism or any diseases that might impact their peripheral nerves.

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Participants completed questionnaires about their sensory perception and underwent tests of their sensory nerves, such as a heat test to check the electrical signals produced by the nerves. They also had skin biopsies to search for damage to the small fibers in their nerves.

The researchers found that 53 percent of the people on the autism spectrum showed reduced nerve fiber density on the skin biopsy, a result that none of the members of the control group had. The participants with reduced nerve fiber density also tended to feel pain on the heat test at a higher heat than the control group did.

“This indicates that the nerves have degenerated, similar to what happens for people with the condition of peripheral neuropathy, where the threshold for feeling heat and other sensations is higher than for other people,” Hsieh said.

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The study also found that people on the autism spectrum had different responses to touch based on whether or not they had nerve fiber damage. Those with normal nerve fibers were more likely to dislike being touched and have an aversion to certain textures, whereas those with nerve fiber damage were more likely to prefer going barefoot and to sometimes be unaware of small injuries like scratches and bruises.

Larger studies involving both sexes will be needed to corroborate these results, but it would appear that the status of the peripheral nerve fibers has an impact on the aversions and behaviors of people on the autism spectrum. This knowledge may be useful for future research and therapeutic techniques.

The study was published in an online issue of Neurology, the medical journal of the American Academy of Neurology.

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