Given that vision and hearing are vital in day-to-day living, an individual generally notices any impairment of these senses right away. Regardless of the fact that various known genetic mutations can result in hereditary vision and hearing defects, little knowledge exists about the sense of touch as defects may not be as obvious, and therefore may go unnoticed.

The first edition in May of the online, open-access journal PLoS Biology reveals that differences in touch sensitivity caused by genetic factors can also be inherited. Researchers at the Max Delbrück Center for Molecular Medicine (MDC) in Berlin have discovered that some of these factors also influence hearing, which implies that a single mutation could potentially affect both senses.

There are valid reasons to believe that hearing and touch may share a common genetic basis as sound-sensing cells in the ear detect vibrations and transform them into electrical impulses, whilst nerves located just below the skin’s surface can detect movement and changes in pressure and subsequently generate impulses. Given the similarity of both systems suggests that they could potentially share a common evolutionary origin, i.e. which could be based on an overlapping set of molecules that transform motion into signals that are transmitted to the brain via the nerves.

In collaboration with medical schools in Hannover, and at the Charité in Berlin and the Hospital Universitario La Fe in Valencia in Spain, Henning Frenzel from Gary Lewin’s laboratory conducted a classical ‘twin study’ to research whether a hereditary basis for touch sensitivity exists. They compared the touch and hearing abilities of identical twins who share identical sets of genes, including any mutations, which may cause defects with the touch and hearing abilities of fraternal twins, other family members, as well as a wider set of subjects.

The findings revealed a considerable hereditary trend in terms of sensitivity to touch, which was strongly connected to hearing ability. This meant the better the sensitivity to touch, the better their hearing, whilst poor hearing was associated with a poor sensitivity to touch.

The participants were exposed to a high frequency vibrating stimulus during the study to examine their hearing ability. In another experiment, the participants were asked to press their finger onto fine gratings with ridges that were spaced at intervals ranging from less than millimeter to almost a centimeter in order to assess their sensitivity of touch. The better the individual’s touch acuity was, the finer was the grating they were able to perceive.

Lewin declared:

“We found a strong correlation between touch and hearing acuity in healthy human populations. Additionally, about one in five young adults who suffered from congenital deafness had poor touch sensitivity.”

Blind participants who were used as controls were often noted to have an enhanced perception of touch, which is logical, given that the genetic basis of vision depends on proteins called photoreceptors, which detect light instead of motion.

The team observed that participants who suffered from Usher’s syndrome, a hereditary condition that results in both deafness and blindness, also had a considerably impaired sense of touch, which indicates that the USH2A gene, which is mutated in the syndrome, is involved in both touch and sound sensations. There are potentially many more genes that affect both types of perception.

According to scientific literature, about 60 mutations in known genes have been associated with hearing impairment, whilst around 60 more DNA alterations exist, which have a similar effect but which have not yet been clearly linked to a gene.

Lewing stated:

“Our next task will be to investigate some of these other cases to see if they are also correlated with problems in touch. This will give us a better understanding of the genetic mechanisms that underlie both types of perception.”

Written By Petra Rattue