According to a study conducted by Dr. Henning Frenzel and Professor Gary R. Lewin of the Max Delbrück Center for Molecular Medicine (MDC) Berlin-Buch, Germany, two of the 5 human senses - hearing and touch - have a common genetic basis.
In individuals with Usher syndrome, the researchers identified a gene variation that is also responsible for the patients' impaired touch sensitivity. Usher syndrome is a genetic disorder characterized by deafness and gradual vision loss. In total the team evaluated sensory function in 518 volunteers.
The researchers note that both hearing and touch rely on the transformation of mechanical force into electrical signals. When we hear, sound waves travel down the ear canal and hit the eardrum causing it to vibrate. This vibration stimulates the hair-like nerve endings in the cochlea to fire off electrical signals to the brain via the auditory nerve. Likewise, when we touch, sensory receptors in the skin transform vibrations into electrical signals and transmit them to the brain.
In recent years, researchers have identified around 70 gene mutations in humans which trigger hearing loss or deafness.
Professor Lewin explains:
"Surprisingly, no genes have been found that negatively influence the sense of touch."
The researchers first examined 100 pairs of twins (66 pairs of identical twins and 34 non-identical twins) in order to determine whether the sense of touch also has a hereditary component. The tests showed that the touch sensitivity of the subjects was determined to more than 50% by genes. In addition, the team found an association between the sense of hearing and touch.
As a result, the team suspected that genes that influence the sense of hearing may also influence the sense of touch.
The researchers then enrolled 39 students in Berlin with congenital hearing impairment in order to evaluate touch sensitivity. The team compared these with results from their twin study and found that not all of the participants with impaired hearing had impaired tactile acuity.
Professor Lewin said:
"Strikingly, however, many of these young people did indeed have poor tactile acuity."
According to the researchers, they focused specifically on patients with Usher syndrome, as it would take a significant amount of time to examine which of the approximately 70 genes that negatively affect the sense of hearing may also adversely affect the sense of touch. Usher syndrome is genetically very well researched and there are 9 known Usher genes variants which cause the disease.
After examining two cohorts of Usher patients, one at the Charité, Universitätsmedizin Berlin, and the other at the university hospital La Fe in Valencia, Spain, the researchers found that not all individuals with the disorder have poor tactile acuity and touch sensitivity.
Touch sensitivity was only found in Usher-syndrome patients who have a mutation in the gene USH2A. This variation is also responsible for the impaired hearing of 19 participants. The team found that 29 patients without the variation had a normal sense of touch. According to the researchers, results from the study indicated that hearing and touch have a common genetic basis, and that more genes that influence both mechanosensory traits will be identified in the future.
During their 5-year study the team also found another interesting detail. Professor Lewin explains:
"When women complain that their men are not really listening to them, there is some truth in that. The studies with a total of 518 individuals including 295 women have actually shown that women hear better and they also have a finer sense of touch than men; in short woman hear and feel more than men!"
Written By Grace Rattue