Touch sensitivity is hereditary and linked to genetic mechanisms that support hearing
Vision and hearing are so crucial to our daily lives that any impairments usually become obvious for an affected person. A number of mutations in genes governing these types of perception lead to hereditary defects in humans. But little is known about our sense of touch, where defects might be so subtle that they go unnoticed. In the May 10 issue of PLOS Biology, Gary Lewin’s laboratory at the Max Delbrück Center for Molecular Medicine (MDC) in Berlin demonstrates that differences in touch sensitivity arise from genetic factors that can also be inherited. Some of these factors support hearing as well, meaning that a single mutation may impair both senses.
There are good reasons to suspect that hearing and touch might have a common genetic basis. Sound-sensing cells in the ear detect vibrations and transform them into electrical impulses. Likewise, nerves that lie just below the surface of the skin detect movement and changes in pressure and generate impulses. The similarity suggests that the two systems might have a common evolutionary origin – they may depend on a common set of molecules that transform motion into signals that can be transmitted along nerves to the brain.
In the current study, Lewin’s lab and collaborators at medical schools in Berlin (Charité), Hannover, and Valencia, Spain (Hospital Universitario La Fe) carried out a classical “twins study” to try to discover a hereditary basis for touch sensitivity. The project compared the touch and hearing acuity of identical twins (who have identical sets of genes, including any mutations that might cause defects) with that of fraternal twins, other family members, and a wider set of subjects. They discovered a significant hereditary trend in touch sensitivity, and this correlated strongly to certain types of hearing problems.
“We found a strong correlation between touch and hearing acuity in healthy human populations,” Lewin says. “Additionally, about one in five young adults who suffered from congenital deafness had very poor touch sensitivity.” Blind subjects used as controls, on the other hand, often had enhanced touch perception. This made sense because the genetic basis of vision depends on proteins called photoreceptors that detect light rather than motion.
During the tests, subjects were exposed to vibrations of various frequencies; another experiment had them run their fingers over a fine grating with ridges spaced at intervals of about a millimeter.
One group of subjects suffering from Usher’s syndrome, a hereditary condition that leads to both deafness and blindness, had a significantly impaired sense of touch. This suggests that the gene USH2A, which is mutated in the syndrome, contributes to sensations of both touch and sound. There are likely to be many more genes that play a role in both types of perception.
The scientific literature reports about 60 mutations in known genes that have been linked to hearing impairment, and about 60 more alterations in DNA with a similar effect that haven’t yet clearly been linked to a gene. “Our next task will be to investigate some of these other cases to see if they are also correlated to problems with touch,” Lewin says. “This will give us a better understanding of the genetic mechanisms that underlie both types of perception.”
An earlier study by the labs of Gary Lewin and Carmen Birchmeier at the MDC showed that while defects in touch sensation don’t seem to cause serious problems for people, those affected may be aware of them. “A number of subjects report problems in gripping objects – they may need to watch their hands as they grasp something,” Lewin says.
– Russ Hodge
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