Injecting virus helps mice hear again

Mouse with large ears
Thanks to this gene therapy I might be able to hear again Image credit: Rasbak/Wikimedia Commons

Deafness is the world’s most frequent sensory disorder. Half of people who lose their hearing before they begin to speak (prelingual deafness) do so due to genetic causes. There are two broad categories of hearing loss: conductive or sensorineural. Conductive losses are due to problems with the middle ear – the ear drum and the ossicles (the small bones that help transmit sound from the air to the inner ear. Sensorineural hearing loss is when there is damage to the inner ear or to nerve pathways from the inner ear to the brain.

Deterioration of the inner ear can be caused by exposure to noise and medical history is also a factor, however there is also a genetic element to play as well. So there two ways that genetics can affect deafness, either it will arrive quickly before you can speak or you can be predisposed to your inner ear’s transmission of sound to the brain failing.

Currently there are three main ways to combat hearing loss: hearing aids which amplify sounds, prostheses which help in the conduction of sound either actively or not, and cochlear implants which directly stimulate neurons. This latter is to compensate for permanent damage to the primary sensory hair cells (these help convert the mechanical motion do to the sound vibrations into electrical signals which the brain process) or damage to the auditory nerve. These techniques go a long way in helping sufferers of hearing loss, but are far from optimal. They might have poor frequency sensitivity, may not allow for natural sound perception or allow for speech to be discerned easily in noisy environments.

It has been proposed that gene therapy, which was once the realm of sci-fi (they use it in Stargate to allow the Atlantis crew to use alien technology!) but with the recent advances in techniques such as CRISPR or more importantly here adeno-associated vector (AAV) treatment, may allow this to become a reality. AAV (a synthetic virus) is injected into a site and infects nearby cells altering their genome in a prescribed manner.

A collaboration including researchers from Harvard University and UCL injected a solution of some of these viruses into the inner ears of mice and found that the injection into the mouse ear was well tolerated and did not negatively affect their hearing compared to healthy mice, and the mice were found to have a large uptake of the virus’s genome. This is a big step forward for gene therapies to the inner ear as the delicate chemistry of the inner ear would need to tolerate this injection. This research paves the way for clinical trials to attempt to restore hearing in mammals with this method.

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