The mechanisms of the inner ear are some of the most delicate parts of your body, and once damaged by loud noise or disease are incapable of re-growing. However, in the next few months, human trials are due to start for a gene therapy which is hoped will be able to restore hearing to the deaf.
The mechanisms of the inner ear involve a series of cells with long thin strands called hair cells, which are present in the area of the ear known as the cochlea. Vibrations which are picked up by the ear drum are transferred to the cochlea via a trio of tiny bones, and the movement of the hair cells is translated by the brain into audible sound. When these hair cells are eroded, deafness occurs.
At the University of Kansas, researchers have engineered a type of virus which is capable of inserting a DNA strand into a specific section of the human genome. In this case, the DNA sequence is the Atoh1 gene, which in normal development is linked to the growth of hair cells. By using the virus to re-activate the Atoh1 gene, the team were able to drastically improve the hearing in deafened mouse subjects by around 20 decibels. This improvement is roughly equivocal to holding your hands over your ears, compared to normal hearing.
The treatment is only viable in patients who were born with hearing and lost it in later life, as all the necessary neurological connections would still be in place. Sufferers born with deafness would still have to rely on hearing aids or cochlear implants. Regardless, if the trials prove successful, it would be a huge leap not only for treatment of deafness but also for gene therapy. Up until very recently, using gene therapy of this type was only a speculative treatment, and if it can be shown to work on a condition as common as loss of hearing, it will be a significant step forward.