A gene that contributes to one of the commonest causes of deafness has been identified for the first time, in a step towards improving diagnosis and treatment.

People with otosclerosis, the most common reason for hearing loss among white adults, are more likely to carry a particular variant of a gene called TGBF1 than those who are unaffected, scientists in Belgium have discovered.

The findings, from a team based at the University of Antwerp, promise new insights into the origins and development of the condition, which usually begins in the twenties or thirties and affects about one in 250 people. In the long term, that could lead to new ways of preventing and treating otosclerosis, for which the best option today is usually an operation that is not always effective. One of the most attractive prospects would be to use the new genetic clue to design a drug that stops the progression of otosclerosis before it causes potentially irreversible tinnitus and hearing loss.

Much more research is still needed to confirm the effect, to establish how it influences the disorder, and to develop a drug. Melissa Thys, who led the study team, said that it could be ten years before the results have an impact on medicine.

Otosclerosis is known to be affected by genetic and environmental factors. TGBF1 is the first gene to be conclusively linked to it. The find is especially promising because the gene is known to be involved in the embryonic development of the ear and influences a pathway that appears important to the progression of otosclerosis.

The condition involves abnormal bone growth in the middle ear, which impairs movement of the stapes or “stirrup” – the last of the three tiny bones that transmit sound to the inner ear. It generally causes tinnitus and the loss of hearing at lower frequencies.

Ms Thys, who presented the research to the European Society of Human Genetics conference in Nice yesterday, said: “The gene in which the variant is located points to a pathway that contributes to the disease. This may be a lead for better forms of treatment in the future. Currently the best option is an operation. However, there is often an additional component of hearing loss, which can’t be restored by surgery. As the gene involved is a growth factor, and the disease manifests itself by the abnormal growth of bone in the middle ear, it may have a large potential for therapy.”

In the study, Ms Thys’s team compared 630 patients with otosclerosis with the same number of unaffected controls in Belgium and the Netherlands. They found that a protective variant of TGBF1 was carried by 7 per cent of healthy subjects, compared with only 2.5 per cent of the otosclerosis group. The data has been confirmed in a French group of 457 patients and 497 controls.

Ms Thys said: “Combining the data from both groups with a common odds ratio gave a significant result, from which we were able to conclude that we were the first to identify a gene that influences the susceptibility for otosclerosis. And, as further evidence, we were also able to show that a more active variant of this gene is protective against the disease.”

Catriona Crombie, of the Royal National Institute for Deaf People, welcomed the findings. “The discovery of this gene responsible for a common cause of hearing loss is a fantastic breakthrough,” she said.

“The effects of otosclerosis can be devastating – imagine the frustration of incessant ringing in your ears, or of being constantly asked to ‘speak up’.

“Researchers can now focus their effort on this gene and the processes it controls to develop new ways of preventing and treating otosclerosis.”

“If a drug could be developed for this devastating condition, it could save many from repeated painful surgery. This study highlights the vital role genetic research can play in helping us understand the causes of many types of hearing loss, which could lead to ways of protecting and restoring hearing .”

In numbers

8,945,000 deaf and hard of hearing adults in Britain
1m people, or about 2 per cent of the UK population, is affected by otosclerosis
2m people have hearing aids, although only 1.4 million use them regularly

Source: RNID

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