The search for new therapies for deafness has taken a significant step forward after scientists successfully grew a critical type of ear cell in mammals for the first time.

The achievement, by a team whose leader is himself profoundly hard of hearing, offers the best indication yet that it is possible to regenerate ear hair cells that are the key to most hearing impairment.

Between 60 and 90 per cent of cases of deafness and hearing loss are caused by damage to hair cells in a part of the inner ear called the cochlea that pick up sound and activate the nerves that transmit this sensory information to the brain. The damage can also contribute to tinnitus – a ringing in the ears that affects about seven million Britons.

The human cochlea has about 15,500 of these hair cells, which can be damaged by ageing, excessive noise, genetic defects and certain drugs and infections. The cells do not regenerate, so this damage causes progressive and irreversible hearing loss, sometimes leading to complete deafness.

Times Archive, 1922: The renewed illness of the Duke of Wellington, 1822

A violent remedy, applied to or poured into the ear, to cure a temporary deafness, is said to have wholly affected his head

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The findings, which are published in the journal Nature, will offer hope of new treatments to many of the nine million people in Britain and 250 million worldwide who are deaf or hard of hearing.

The work was headed by John Brigande, of Oregon Health and Science University in the United States, whose hearing has been deteriorating progressively since he was aged 10. He said: “My hearing loss is an enormous challenge in both my personal and professional lives. I have hope that there will be new restorative therapies for hearing loss in my lifetime.”

The Oregon group used gene therapy to grow working hair cells in mouse embryos in the womb. When the mice were born, they had more working cochlear hair cells than they otherwise would have done. The scientists have also established that these cells, which were created by manipulating a gene called Atoh1, have all the characteristics of healthy hair cells.

While the technique still requires much refinement before similar methods can be considered for human trials, it provides the first proof of principle that hair cells can be grown from scratch in mammals.

The researchers have now begun experiments to test whether the technique can reverse the effects of genetic mutations that make mice deaf. If these succeed, they hope to create better mouse models for investigating human hearing loss, and eventually to develop ways of regrowing hair cells and reversing deafness in humans.

“There is intense interest in cell replacement strategies to ameliorate the effects of inner ear disease, but until now we didn’t have direct evidence indicating we could make a functional sensory hair cell,” Dr Brigande said.

“We have the first step down: we can induce functional sensory hair cells to form. Now, we need to learn if it’s possible to restore hearing in a deaf mouse mutant, experiments that are ongoing. We know it’s possible to generate sensory hair cells that function, and that’s an important step toward defining rational therapies in humans. I am profoundly hard of hearing. The exciting news for those of us with hearing loss and tinnitus is that we now have hope of having our hearing restored some day.”

The gene therapy technique might conceivably be combined with research into embryonic stem cells and reprogrammed adult cells, to create new hair cells that could be implanted to restore hearing. Another approach might be to directly manipulate genes in the inner ear to encourage the formation of new hair cells.

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