In general, autism spectrum disorders (ASD) is understood to be caused by differences in brain development, and that it is from this that all the typical behaviors associated with the condition derive. But a recent study on mice suggests that this might not be the whole picture. Researchers are proposing that at least some aspects of the condition are linked not to the brain, but to the nerves in the peripheral body, including those in the limbs and those that sense touch from the skin.
“An underlying assumption has been that ASD is solely a disease of the brain, but we've found that may not always be the case,” explains David Ginty, a Professor of Neurobiology at Harvard Medical School and senior author of the new study published in Cell. “Advances in mouse genetics have made it possible for us to study genes linked to ASD by altering them only in certain types of nerve cells and studying the effects.”
The study found that some of the aspects linked to autism, such as the perception of touch and anxiety, might be down to nerve cells. They looked at genes commonly associated with the condition in humans – Mecp2, Gabrb3, Shank3, and Fmr1 – and found that mice with mutations in these same genes experienced altered ability to discriminate between different textures, as well as hypersensitivity to gentle touch. In addition to that, they found that the transmission of the neural impulses from the touch neurons in the skin to the spinal column was also altered. When the mice were engineered to express these mutations only in the brain, and not in their neurons, they found that there were no differences in the rodents' touch perception.
They then looked at how the mutations in these specific genes altered the rodents' social interactions. Interestingly, they found that the mice showed increased signs of anxiety, and interacted less with other mice. “A key aspect of this work is that we've shown that a tactile, somatosensory dysfunction contributes to behavioral deficits, something that hasn't been seen before,” says Ginty. “In this case, that deficit is anxiety and problems with social interactions.”
How this study – which was conducted solely in mice – then translates into humans is still, however, up for debate as is often the case when research is conducted on rodents. For example, ASD doesn’t express itself in the same way in all people, so this experiment may only be relevant to a small selection, if it is relevant at all. But it does raise interesting questions about some aspects of the condition, and about anxiety in general. Could our sensory experiences of touch be impacting our social interactions with other individuals?