Gene Mutation and Hearing Loss

In France, one child in a thousand is born with profound deafness. But hearing loss or deafness can also occur temporarily or permanently during life, regardless of age. Recently, French researchers highlighted a link between a genetic mutation and the predisposition to hearing loss. Explanations.

Hearing and deafness

Hearing loss or deafness is defined as a decrease in hearing capacity. It can occur in childhood or later in life, under different circumstances, and be temporary or permanent. Hearing loss is calculated by the number of decibels lost in the perception of sounds, and makes it possible to distinguish several levels of deafness:

  • Mild deafness between 20 and 39 decibels of hearing loss;
  • Average deafness, between 40 and 69 decibels;
  • Severe deafness, from 70 to 89 decibels;
  • Profound deafness, beyond 90 decibels of hearing loss.

Deafness, from the level of average deafness, has consequences on daily life, and represents one of the forms of invisible disability. Several factors or events in life can lead to hearing loss, temporarily or permanently, such as serous otitis in young children, or aging in the elderly.

Gene Mutation and Hearing Loss

Faced with the risk of hearing loss, all individuals are not equal. A recent study by French researchers suggests that genetic mutations could promote hearing loss and its evolution over time. The research team specializes in studying the pathophysiological mechanisms responsible for hearing disorders. Recently, she looked at the mutation of a particular gene, the THRA gene, in a mouse model.

The THRA gene codes for a thyroid hormone receptor, including triiodothyronine, which plays an important role in the development of part of the inner ear, the cochlea. Mutation of the THRA gene could therefore be likely to disrupt the development of auditory functions. Previous studies had revealed that mutations in the THRA gene could be responsible in particular:

  • Growth retardation;
  • Bone malformations.

But no data had linked the mutation of this gene with hearing problems.

The mutation of the THRA gene, a predisposing factor for deafness?!

In this new study, the researchers observed the consequences of a THRA gene mutation in mice. They demonstrated that certain cells in the inner ear of mice, the outer hair cells, were abnormally implanted in the ear. These cells normally have the function of amplifying sound vibrations and allowing a better perception of different sound frequencies.

Researchers’ discovery in mice carrying the THRA gene mutation

In mice carrying the THRA gene mutation, the researchers noted a loss of perception of high frequencies and a decrease in the number of nerve fibers in the auditory nerve. In addition, the outer hair cells of these mice appeared more fragile than normal in the face of several auditory stresses recognized for their deleterious effects on hearing :

  • Excessively loud sounds;
  • Ototoxic drugs, i.e. capable of damaging hearing (for example certain antibiotics);
  • Oxidative stress associated with aging.

Such results seem to suggest that carriers of a THRA gene mutation may be predisposed to hearing loss. The researchers will continue their work by studying the hearing of people affected by this type of mutation to confirm or not in humans the observations made in mice. A better understanding of the mechanisms involved in the development of hearing loss could allow the development of new, more targeted therapies.

Estelle B., Doctor of Pharmacy

Sources

– Deafness: identification of a new genetic risk factor. inserm.fr. Accessed September 1, 2022.
– A disease-associated mutation in thyroid hormone receptor α1 causes hearing loss and sensory hair cell patterning defects in mice. science.org. Accessed September 1, 2022.
– Deafness and the causes of hearing loss. ameli.fr. Accessed September 1, 2022.

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