“Your hearing loss is permanent.”
For most patients with hearing loss, this is the dreaded statement from their hearing care professional. There is no cure for sensorineural hearing loss, the most common form of hearing loss. Currently, the only method of rehabilitation is amplification via hearing aids, cochlear implants, or assistive listening devices.
With hearing loss due to aging, excessive noise exposure, ototoxic medication, or genetics, the damage most often occurs in the inner ear, also called the cochlea. Inside it are rows of sensory cells responsible for hearing, called hair cells. When these are damaged or destroyed, the hearing loss is irreparable — at least in humans.
For about 20 years now, scientists have known that in many species of birds, damaged hair cells grow back. Hair cells in deafened birds like chickens can heal, allowing them to hear again after some time. Studies have shown that when exposed to auditory trauma, supporting cells in the birds’ inner ears can produce or even transform into sensory cells that become capable of detect sound. Since then, we’ve discovered that birds, reptiles, and even some fish have exhibited spontaneous hair cell regeneration. Unfortunately , this ability in mammals is limited.
Naturally, with these discoveries, scientists are working to understand the underlying mechanisms involved in hair cell regeneration, and how it can be applied to hearing loss in humans. Their progress so far is promising. In 2013, Dr. Albert Edge and his team made an “accidental” discovery during their studies on dementia. They found that a certain type of molecule can produce new hair cells in culture, which were then able to help mice hear better. With these findings, Dr. Edge is working on developing a drug that can be applied to the human inner ear to regrown hair cells. His studies have shown enough promise to garner funding from the European Union.
On this side of the Atlantic, a company based in Connecticut is also looking to drugs that can encourage supporting cells in the human inner ear to produce and become sensory hair cells, in a process much like that observed in birds. Furthermore, gene therapy is also being examined as a way to regrow hair cells in humans. In fact, the first step in this approach has been achieved: the gene responsible for stimulating hair cell growth has already been identified.
Considering that the possibility of hair cell regeneration was only discovered 20 years ago, amazing progress has already been made by scientists around the world. While we marvel at the pace with which hearing aids and other assistive devices have improved, researchers in the medical and pharmaceutical fields are also racing to develop the first drug or procedure that can cure hearing loss.
Perhaps, in the not-so-distant future, sensorineural hearing loss will become as reversible as a broken bone!