Scientists have found a single gene they believe could hold the key to age-related deafness.
The breakthrough brings the prospect of a treatment to prevent hearing loss, which affects half of people over 60, a step closer.
When the FGF20 gene was taken out in mice, the animals appeared perfectly healthy, but could not hear at all.
The researchers, at Washington University School of Medicine, found two-thirds of their outer hair cells, the delicate cells in the inner ear which amplify sounds, had disappeared.
Damage to these cells is associated with the most hearing loss related to old age, noise exposure and some genetic conditions.
The study suggests this gene – which is also found in humans – could be critical to attempts to growing new hair cells, considered the holy grail of those researching treatments for deafness.
Because our bodies have no way of replacing these cells, there is currently no cure although hearing aids can provide some relief.
However gradual age-related hearing loss still leaves sufferers socially isolated and many take several years to seek help.
The researchers ‘knocked out’ the gene in mice by removing a protein which causes it to develop while they are in the womb.
It is one of a number of genes – called fibroblast growth factors – which are crucial in tissue development and wound healing in embryos.
But removing it at this early stage did not seem to cause any other adverse effects.
In particular, the inner hair cells, which electrically transmit the amplified sounds to the brain, appeared normal.
Lead author Dr Sung-Ho Huh said: ‘This is the first evidence that inner and outer hair cells develop independently of one another.
‘This is important because most age-related hearing loss and noise-induced hearing loss is due to the loss of outer hair cells.’
The next step is to see whether deafness in human is associated with mutations of the same gene, which is already underway.
Professor Karen Steel, an expert in the genetics of deafness at the Sanger Institute in Cambridge, who was not involved in the study, said: ‘The scientific community is very, very interested in developing a way of triggering regeneration of hair cells.
‘They never regenerate once they die, and so there’s a lot of work going on to understand how we can get over that problem, and try to regenerate the hearing.
‘What this study suggests is that FGF20 could be critical for the development of that hair cell, as part of a cocktail of other molecules.
‘I would say regenerating hair cells in humans is between 10 and 20 years away.
It’s a very complicated problem as there are so many genes potentially involved, it’s like a 1,000-piece puzzle, but this brings us a bit closer.’
Rachel Baker of Action on Hearing Loss said: ‘Understanding how cells in the inner ear grow is crucial in developing new therapies for protecting and restoring hearing.
‘We are pleased to be funding a new project being run by this research team, which is further investigating the role of FGF20 in hearing.
‘In the future, this could lead to studies to test whether reactivation of FGF20 can regenerate damaged parts of the inner ear.’