2008-08-30

Deaf people could one day have their hearing restored through a groundbreaking gene therapy technique, a new study suggests. By Roger Highfield.

The transfer of a specific gene is shown today by a milestone experiment to trigger the growth of new hair cells in the inner ear - the usually irreplaceable sensory cells that pick up sound vibrations and that are lost as a result of ageing, disease, certain drugs, and by excessive exposure to loud sound.

The approach, which one day could help millions of people worldwide with deafness and inner-ear disease, is made possible by a technique that is demonstrated in the journal Nature by an American team lead by Dr John Brigande of the Oregon Hearing Research Centre, Portland, who himself is profoundly hard of hearing.

Dr Mark Downs, Director of Science at The Royal National Institute for Deaf People, RNID says: "This is an exciting development which completes another important piece of the jig-saw in understanding how we might use gene therapy to eventually restore hearing loss."

However, he would not be drawn on when the first trials could start in patients.

"Together with the very positive early signs from other potential treatments, such as stem cell therapies, it is no longer just a pipe-dream to talk about cell and drug based solutions to restore hearing. There is a long way to go, but the journey towards new treatments is certainly under way."

Named for the hair-like projections on their surfaces, hair cells form a ribbon of vibration sensors along the length of the cochlea, the organ of the inner ear that detects sound.

Receiving vibrations through the eardrum and bones of the middle ear, hair cells convert them to electrical signals carried to the brain.

People, like all mammals, are not able to regenerate hair cells when they are damaged or lost. Dr Brigande and colleagues show in Nature that by implanting a gene that regulates hair cell growth, Atoh1, into the mouse inner ear while the mouse is still in the womb, new hair cells are made.

Dr Anthony Ricci, a collaborator at Stanford University, showed that the newly formed hair cells function as well as normal hair cells.

As for human tests, Dr Brigande says that the work is at too early a stage to say when they can start: "There is no present plan for tests in humans. The next step is to restore hearing in a deaf mouse.

"Only after this can we start experiments that will teach us if the approach might work in humans. So there is an enormous amount of work to do.

"The exciting news for those of us with hearing loss and tinnitus (ringing in the ears) is that we now have hope of having our hearing restored someday."

He said that some deaf people will reject the offer of gene therapy. "If a person is born without hearing, they are "Deaf" and that is a unique culture into itself. Many Deaf individuals highly value their deafness and do not wish to be hearing.

"I was born hearing, and began to lose my hearing in grade school," he adds. The cause is unknown.

"My hearing loss is progressive, so I need to think about other options in the very near future."

Would he offer himself for the first experiments on patients? "I have never considered self-experimentation to treat my hearing loss. I hope to contribute to an effort that helps define suitable therapies, which may one day be offered in the clinic. That's the right way to go about this."

Normally, humans are born with about 12,000 hair cells in each ear and the death of the cells accounts for most types of acquired hearing loss.

Overall, the steady loss that accompanies the wear and tear of ageing produces significant hearing deterioration in about a third of the population by the age of 70.

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