La mutation du récepteur TRα entraîne une perte de perception des fréquences aiguës, du moins chez la souris. © koszivu, Fotolia

Deafness: Discovery of a new genetic mutation linked to hearing loss

A mouse study reveals a new risk factor for hearing loss. The mutation in question of a thyroid hormone receptor would disrupt the hair cells, which allows us to perceive high frequencies in particular.

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At the level ofinner ear, the cochlea is the organ that integrates sound. Triiodothyronine (T3), which is the active form of a thyroid hormone, plays an essential role in the development of the cochlea and hearing. As always in biology, receptors mediate many signaling pathways. Here the effects of T3 can succeed thanks to the TRβ and TRα receptors, but certain mutations Genoa encoding these receptors likely alter the establishment of auditory functions.

It is already known that mutations affecting TRβ lead to a Resistance to and associated with thyroid hormones deafness in humans and mice. However, much of the role of TRα in auditory function was unknown. To test whether the TRα receptor also affects this function, French researchers introduced human mutation of the TRα-encoding THRA gene into mice.

THRA mutation leads to damaged outer hair cells

It is found that the implantation of certain cells of the structure of the inner ear
The cochlea, whose shape is reminiscent of…” data-image=”” data – url=”” data-more=”Read more”>inner ear animal then becomes abnormal
“, To explain in a press release from Inserm Jing Wang of the Montpellier Neuroscience Institute, co-author of the study. ” it is hair cells external, usually responsible for amplifying vibration types and examples: music…
So a mass attached to a spring, an RLC circuit, a speaker or a molecule…” data-image=” 7/ 0 /570f9ea55b_104266_vibration-loudspeaker.jpg” data-url=”” data-more=”Read more”>vibrations sound and which help to distinguish their different frequencies. This anomaly results in a loss of high frequency perception in mice carrying the mutation.

More specifically, the outer hair cells of the cochleas of these mice were abnormally aligned (about 20%) or absent and appear to be more susceptible to different types of stress: exposure to loud noises, hearing-damaging drugs (so-called “ototoxic”) or even related to oxidative mechanisms with aging. In addition, the researchers report that when the THRA gene mutation is present, there are fewer auditory nerve fibers.

Thus, the TRα receptor is necessary for the proper development and maintenance of outer hair cell function. This suggests that patients with mutations in the THRA gene may be at increased risk of deafness with time. In France, some people have just been identified as carriers of this mutation.

Conduct human trials

To find out if these changes are found in humans, we will receive patients who have been identified with this mutation and run tests that specifically focus on the functionality of their outer hair cells.says Jing Wang. If the hearing assessment of these people shows a comparable impairment as in our model mouse.” -labo-rama-cc-01.jpg” data-url=”https :// /” data-more=”Read the definition”>murinewe will make them aware of the risk taken while we wait to validate all our data. »

In addition to regular hearing checks, these patients are then advised to avoid taking and exposure to ototoxic drugs sound level exaggerated. In the longer term, increasing the number of functional hair cells could be an interesting therapeutic approach.

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