Scientists identify gene involved in hearing loss

Researchers at the University of Wisconsin, US have discovered that a gene called Bak contributes to age related hearing loss (AHL). Their findings, published in the Proceedings of the National Academy of Sciences, report that deleting the gene in mice appears to save the hair cells, resulting in fewer hearing defects.

As we age we steadily lose the hair and nerve cells in our ears. These cells cannot be replaced, which means we often begin to notice a decline in our hearing ability. AHL currently affects 50 per cent of people in Britain aged 60 years and over. Currently the only treatment option available for someone affected by hearing loss is a hearing aid that will amplify sound. However this doesn't offer any hearing recovery and cannot function like the human ear so the wearer can sometimes find it hard to single out one sound from all the surrounding background noises.

Research into the Bak gene has found that it is capable of activating this detrimental hair and nerve cell death. Dr Shinichi Someya and colleagues believed it could be an important gene in AHL and so genetically engineered mice to be lacking in the Bak gene. They then tested the hearing ability of the mice at 12-15 months of age, when they would usually expect to observe AHL and compared it to normal animals. The group found that mice missing the Bak gene had much less hair and nerve cell death and so had better hearing.

To try and identify how Bak was playing its role in cell death they isolated some cells from the cochleas of the normal mice, and subjected the cells to chemicals known to cause oxidative stress (by-products of energy production in the cell that cause DNA and protein damage). They found that Bak was activated by the oxidative stress, so the mice lacking Bak were resistant to oxidative damage. The group supported this finding by showing antioxidant supplements (for example coenzyme Q10) fed to the mice helped to reduce the activity of Bak and so slowed the development and progression of AHL.

Whilst the results are very encouraging and gives hope that a target for treatment may have been found, it is important to remember that all of these experiments have so far been limited to mice. The situation in human hearing loss may be much more complex and require other gene targets.

Dr Ralph Holme, of the Royal National Institute for Deaf People, said: 'This research is an important step towards finding effective ways to halt age-related hearing loss.' But he acknowledged further research was needed to 'gauge the real significance of these findings to the human population'.