Gene Mutation Leads to Impairment of Two Senses: Touch and Hearing
In all vertebrates, and consequently also in humans,
hearing and touch represent two distinct sensory systems that both rely on the
transformation of mechanical force into electrical signals. When we hear, sound waves trigger vibrations that stimulate
the hair-like nerve endings in the cochlea in the inner ear. These then transform
the mechanical stimuli into electrical signals, which are transmitted to the
brain via the auditory nerve. When we touch something a similar process takes
place: The mechanical stimulus — sliding the fingers over a rough or smooth
surface, the perception of vibrations — is taken up via sensors in the skin, converted
into an electrical stimulus and transmitted to the brain.
Twin study with 100
pairs of twins
In recent years about 70 genes have been identified in
humans, mutations in which trigger hearing loss or deafness. “Surprisingly, no
genes have been found that negatively influence the sense of touch,” Professor
Lewin said. To see whether the sense of touch also has a hereditary component, the
researchers first studied 100 pairs of twins — 66 pairs of monozygotic twins and
34 dizygotic pairs of twins. Monozygotic twins are genetically completely
identical; dizygotic twins are genetically identical to 50 percent. The tests
showed that the touch sensitivity of the subjects was determined to more than
50 percent by genes. Furthermore, hearing and touch tests showed that there is
a correlation between the sense of hearing and touch.
The researchers therefore
suspected that genes that influence the sense of hearing may also have an
influence on the sense of touch. In a next step, they recruited test subjects
at a school in Berlin for students with hearing impairments. There they assessed
the touch sensitivity in a cohort of 39 young people who suffered from severe congenital
hearing impairment. The researchers compared these findings with the data from
their twin study and discovered that not all of the young people with hearing loss
had impaired tactile acuity. “Strikingly, however, many of these young people did
indeed have poor tactile acuity,” Professor Lewin explained.
The researchers decided it
would take too much time to analyze which of the approximately 70 genes that
adversely affect the sense of hearing may also negatively affect the sense of
touch. Therefore, the researchers focused specifically on patients with the
Usher syndrome, a hereditary form of hearing impairment, in which the patients progressively
become blind. Usher syndrome patients have varying degrees of hearing
impairment, and the disease is genetically very well studied. There are nine known
Usher genes carrying mutations which cause the disease.
The researchers examined one
cohort of patients in a special consultation at the Charité — Universitätsmedizin
Berlin for Usher patients from all over Germany. A second cohort was recruited
at the university hospital La Fe in Valencia, Spain. The studies revealed that
not all patients with Usher-syndrome have poor tactile acuity and touch
sensitivity. The researchers showed that only patients with Usher syndrome who
have a mutation in the gene USH2A have poor touch sensitivity. This mutation is
also responsible for the impaired hearing of 19 patients. The 29 Usher-syndrome
patients in whom the mutation could not be detected had a normal sense of
touch. The researchers thus demonstrated that there is a common genetic basis
for the sense of hearing and touch. They suspect that even more genes will be
discovered in the future that influence both mechanosensory traits.
Women hear better
than men and have a finer sense of touch
The researchers discovered another interesting detail
during their five-year study. “When women complain that their men are not
really listening to them, there is some truth in that,” Professor Lewin said. “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!”
*A genetic basis for mechanosensory traits
in humans
Henning Frenzel1, Jörg Bohlender2,
Katrin Pinsker2, Bärbel Wohlleben2, Jens Tank3,
Stefan G. Lechner1, Daniela Schiska2, Teresa Jaijo5,
Franz Rueschendorf4, Kathrin Saar4, Jens Jordan3,
José M. Millán5 and Manfred Gross2, Gary R. Lewin1,6
1Department of Neuroscience, Max Delbrück Center for
Molecular Medicine, Robert-Rössle-Str. 10, Berlin-Buch D‑13092 Germany, 2Department
of Audiology and Phoniatrics, Charité, Universitätsmedizin, Berlin,
Augustenburger Platz 1, Berlin D‑13353 Germany. 3Institute of
Clinical Pharmacology, Hannover Medical School, Carl-Neuberg-Str. 1, Hannover
D‑30625, Germany, 4Experimental genetics of cardiovascular disease,
Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin-Buch
D‑13092 Germany, 5Genetics Unit, Hospital Universitario La Fe, Avda.
de Campanar, 21, 46009 and CIBERER, Valencia, Spain
6Author for Correspondence
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