New advances in gene therapy are giving fresh hope to people who have gone deaf or are hard of hearing.
Scientists working in America have published studies which show remarkable results from early experiments aimed at restoring hearing in mice. Previously deaf mice were able to hear sounds as quiet as a whisper after being given the therapy.
The research could pave the way to restoring near-normal sound detection for many people who have lost their hearing and is being described as “landmark” work.
Published in respected medical journal “Nature Biotechnology”, the research explains how scientists were able to correct defects which led to microscopic sound-sensing hairs deep in the ear becoming damaged and ineffective. They used a man-made synthetic virus to correct the defect and restore the hairs, which in turn restored hearing to near-normal levels.
However, the scientists stress the research – while very promising – is still at an early stage, will not work for all types of deafness and hearing loss, and will need to be monitored to see how long it remains effective.
About half of all types of deafness are caused by errors in our DNA – the basic building blocks which determine how our bodies work. The experiments carried out at Harvard Medical School and Boston Children’s Hospital first isolated which errors in DNA could lead to loss of hearing.
The mice used in the experiments had a genetic disorder called Usher syndrome, which means a fault in their DNA was sending inaccurate instructions for growing the microscopic sound-detecting hairs inside their ears. In other words, it made them deaf.
In fully functioning ears there are sets of outer hair cells which magnify sound waves and inner hair cells which convert the sound to electrical signals to send to the brain. The hairs normally grow in neatly-ordered rows of V-shaped ‘clumps’, but in Usher syndrome they become disorganised and ineffective, seriously damaging hearing ability.
The synthetic virus developed by the scientists ‘infects’ the ear with the correct genetic instructions for growing the hair cells, helping restore the neat and effective rows of V-shaped clumps. After being given the virus, mice that had been profoundly deaf were able to hear sounds as low as 25 decibels – about the volume of a whisper.
Questions remain over whether the synthetic virus is safe for use in humans, but it is based on a virus which has already been successfully used in other types of gene therapy. It is also early days for knowing how long its effects will last, but the scientists know it lasts at least six months. More work is also needed on making the synthetic virus effective at different stages of a recipient’s life.
One of the American researchers, Dr Jeffery Holt, said: “We’ve really gotten a good understanding of the basic science, of the biology of the inner ear, and now we’re at the point of being able to translate that knowledge and apply it to human patients in the very near future.”
The research has been tentatively welcomed by Action on Hearing Loss, the UK’s largest charity helping people confronting deafness and hearing loss. Its director of research, Dr Ralph Holme described the studies as “very encouraging”, but stressed the treatment wouldn’t be effective for all types of hearing loss.
“The technology may be better suited to treating more progressive forms of hearing loss, “he said.