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Doctors have moved one step closer to treating previously irreversible hearing loss after discovering a ‘master gene’.
The breakthrough gives hope to the 11million Britons living with deafness due to ageing, noise damage or as a consequence of certain medications.
Until now the condition has proven untreatable because scientists have not been able to reprogram cells to develop into the outer and inner ear sensory cells to regrow lost hair.
But experts in the US say they have now discovered a single gene called TBX2 that governs the type of hair ear cells grow through tests on mice.
Professor Jaime Garcia-Anoveros, a neurologist at the Northwestern University in Chicago and lead author of the study, said: ‘We have overcome a major hurdle.’
The discovery could open the door to gene therapies capable of reprogramming cells to reproduce the lost hair inside people’s ears.
Scientists have discovered the specific gene that governs if an ear hair cell grows into an inner or outer hair. With our sense of hearing relying on a careful balance between the two being unable to artificially grow one or the other was a major hurdle in developing potential treatments for deafness (stock image)
Our sense of hearing is governed by two types of tiny hairs located in the ear called outer and inner hair cells.
Outer hair cells amplify sound for the inner hair cells, which then transmit vibrations as signals to the brain which translates the message into sound.
The most common cause of deafness and hearing loss is the death of outer ear hair cells, which happens naturally when we age.
But this can also happen from excessive noise or certain drugs and treatments like antibiotics or chemotherapy.
Hearing loss is a major issue in the UK with about one in six people living with some form of partial or total deafness.
And in the US, about 8.5 per cent of people between the age of 55 and 64 have some form of hearing loss but this rises to 50 per cent among those older than 75.
Through tests on mice Professor Garcia-Anoveros and his team and found that when TBX2 was expressed it directed a hair cell to produce an inner hair cell.
In contrast, when TBX2 was blocked the cell went on to develop an outer ear hair cell.
While stressing research was still at an early experimental stage, Professor Garcia-Anoveros said the discovery could one day help regrow people’s ear hair cells and restore their hearing, as well as uncover more about what causes deafness.
‘We can now figure out how to make specifically inner or outer hair cells and identify why the later are more prone to dying and cause deafness,’ he said.
He said to produce these cells would require a ‘gene cocktail’.
Firstly, genes called ATOH1 and GF1 would be needed to make a cochlear, the part of the ear responsible for receiving sound and converting them vibrations, hair cell from a ‘non-hair cell’, Professor Garcia-Anoveros.
At this point the TBX2 gene could be activated to produce the needed inner or outer ear cell and its corresponding hair.
Professor Garcia-Anoveros said the interaction of the outer and inner ear hair cells to capture sound was like a ballet.
‘It’s like a ballet. The outers crouch and jump and lift the inners further into the ear.’
‘The ear is a beautiful organ. There is no other organ in a mammal where the cells are so precisely positioned. Otherwise, hearing doesn’t occur.’
The scientists findings have been published in the journal Nature.
ARE HEARING PROBLEMS HEREDITARY?
Gene mutations can cause hearing loss in several ways.
Genetic factors also make some people more susceptible to hearing loss than others. Their genes make them more predisposed to hearing loss due to ageing or induced by noise, drugs or infections. It is estimated that the causes of age-related hearing loss are 35-55% genetic.
Examples of hereditary hearing loss causing hearing impairment include Otosclerosis, Usher’s syndrome and Pendred syndrome. You can find more specific information about different syndromes under ‘syndromes of hearing loss’.
Inner ear sensory hair cells play a vital role in our hearing, and mutations in these cells can prevent them from functioning properly, resulting in hearing loss.
Finally, gene mutations may cause several non-hearing related, hereditary conditions combined with a deformation of the inner ear, resulting in deafness at birth or later in life.
Scientists around the world are working to map out the genetic mutations associated with hearing loss and are frequently making new discoveries. Other scientists are experimenting with gene therapies which may become important treatments of hereditary and genetic hearing loss in the future, perhaps in combination with stem cell therapy.