Hearing Disability Linked To Poor Touch Sensitivity

Touch and hearing are very distinct, but German scientists have found a possible genetic link between the two sensory systems.

Superficially, the two senses might seem worlds apart, but both rely on the ability to translate motions - vibrations in the ear and movement and pressure on the skin - into signals to the brain. A common set of molecules or mechanisms might be at work.

To determine if touch sensitivity can be inherited genetically, Henning Frenzel of the Max-Delbruck Center for Molecular Medicine and his colleagues first examined 100 pairs of fraternal and identical twins in a study outlined in the journal PLoS Biology.

They tested the twins on two kinds of touch sensitivity traits: "vibration detection threshold," or how low a vibration the subject could detect with their pinky finger; and "tactile acuity," or the ability to distinguish between two pressure points on the skin that are very close together.

Since the identical twins are genetically identical and the fraternal twins share up to 50 percent of the same genes, any genetic effect on touch should be more pronounced in the former.

Next, Frenzel and his team calculated the heritability of the two traits, a figure that explains the degree to which genetic variation contributed to the variation in the traits seen in the subjects. On average, 28 percent of the differences in tactile acuity and 52 percent of the differences in vibration detection could be chalked up to genetic influence.

Second Experiment
In a second experiment, the scientists found that some - but not all - of a population of young people that were born deaf also had impaired tactile acuity. But since there are about 70 known genes that are involved in hearing impairment, the researchers wanted to focus on a smaller group of genes to test the link between hearing and touch impairment.

Third Experiment - Usher syndrome
The scientists next examined patients with Usher syndrome - a hereditary condition that causes both hearing and visual impairment. They zeroed in on USH2A, one of the nine known genes that, when mutated, cause Usher syndrome.

Of the Usher patients studied, the 19 individuals that had a mutation in USH2A had both impaired hearing and poor touch sensitivity. It's possible then, that this gene may play a role in both touch and sound.

"Our next task will be to investigate some of these other cases to see if they are also correlated with problems in touch," senior author Gary Lewin said in a statement Tuesday. "This will give us a better understanding of the genetic mechanisms that underlie both types of perception."