Hearing loss research

In humans, in common with all mammals, the ability to create new hair cells is lost before birth. However, in fish and amphibians, very similar cells are present and produced throughout life.

In the late 1980s, scientists found that birds possessed the ability to replace hair cells which were damaged by exposure to noise or ototoxic agents, resulting in almost complete cellular and functional recovery. This was the first time that warm blooded animals had been shown to possess this ability and it stimulated a great deal of scientific interest.

More recently, new techniques and the increase in genetic knowledge have led to a number of different lines of research which have raised expectations even further. One of the most significant developments was the discovery that hair cells in the mammalian vestibular or balance system, very similar to those in the hearing system, can be regenerated. 

Hair cell research 

Regeneration of hair cells

Deafness Research UK is supporting research which aims to identify and remove barriers to auditory hair cell regeneration. The ability of bird hair cells to regenerate has opened up a number of avenues of research that are trying to understand why this process can happen in birds and not in mammals. For example, one of our research teams is undertaking a study comparing the damage and repair of hair cells in birds and mammals, which will help identify what factors are involved in this process, and why hair cells cannot be regenerated in mammals.

Another of our teams is currently investigating the role of the gene connexin-43 that prevents new hair cell production in undamaged regions of the bird ear. It is hoped that blocking the effects of this gene in humans will aid in the eventual development of treatments to prevent or even reverse hair cell loss.

In a different line of research supported by Deafness Research UK, scientists are studying newts, amphibians capable of regenerating various body parts, with the aim of isolating chemicals that could stimulate the process in mammalian hair cells.

Development of hair cells

Deafness Research UK researchers are looking at identifying the genes involved in the normal development of hair cells. Some of the genes involved in this process have already been identified, and research is continuing with the aim of controlling cell development and identifying ways of triggering the process when damage has occurred to hair cells. The discovery of many of the genes responsible for hereditary deafness is also opening up significant new lines of research, enabling scientists to identify and study the precise role of some of the proteins needed for the development and functioning of healthy hair cells.

One of the more immediate benefits of this genetic research could be the availability of genetic testing to identify people who are particularly susceptible to hearing loss and who might benefit from preventive therapies of this sort.

Preventing hair cell loss

An alternative to replacing lost hair cells is to prevent their loss in the first place, which is proving to be a particularly promising line of investigation. Deafness Research UK researchers have found that exposure to some ototoxic agents causes cell death by triggering a biochemical 'cell suicide' programme and it is likely that noise, ageing and other ototoxic agents trigger the same process. Because the biochemical pathway is so precise, researchers believe it may be possible to step in to halt it, preventing destruction of the cells. In the laboratory, a number of chemical agents - some quite common, such as aspirin and antioxidants known to protect against damaging chemicals known as "free radicals" - have already been shown to be effective in achieving this.

Despite these developments and the significant progress that has been made in recent years, medical answers for deafness and other hearing problems remain some way off. However, with scientific and medical experts increasingly confident that one day they will become a reality, Deafness Research UK is committed to continuing its support for the research needed to bring them about.

Genetic research

Deafness Research UK has funded research that has lead to a number of breakthroughs in our understanding of inherited deafness in recent years.

Deafness Research UK researchers played an important part in the discovery of genes for a number of syndromal forms of deafness, including the isolation of genes responsible for:

• Waardenburg Syndrome Types I and II
• Treacher Collins Syndrome
• Pendred Syndrome
• Usher Syndrome Type 1b and Type 1c

In 1998, a Deafness Research UK team became the first to identify mutations in a gene called Connexin-26, responsible for at least 10% of European families with a single child affected by non-syndromal sensorineural deafness. The discovery of this gene marked the beginning of an important new phase in our understanding of inherited hearing loss, following to the identification of many of the genes responsible for common forms of hearing loss. Perhaps as many as 100 different genes are thought to be involved in deafness. Mistakes (mutations) in any one of these can then result in deafness. Already more than 20 of these genes have been identified.

Deafness Research UK researchers also carried out a major new study of the genes that cause childhood deafness. The project represented an important step forward in the development of a national strategy for genetic testing and will help determine future priorities for research into the isolation of deafness genes.

Currently we have Deafness Research UK research teams undertaking research into genetic disorders that lead to deafness. One team is working on Branchio-Oto-Renal Syndrome (BOR), caused by a mutation in the gene EYA1. The research will aim to identify other genes that interact with EYA1, which potentially cause other deafness syndromes, and that may also be potential targets for treatment of BOR.

Another team part funded by Deafness Research UK is working on a national study into Usher Syndrome, the major cause of deaf-blindness in the UK. This study aims to correlate the symptoms with the genetic background of the sufferers, which will greatly improve genetic diagnosis of Usher Syndrome and will allow clinicians to give a more accurate prediction of the course of the disease.