Permanent Hearing Loss May Not Always Be So Permanent

As hearing professionals, one of the frustrations we encounter in our practice is that the issues that have caused hearing problems in our patients cannot be reversed. One of the primary reasons for hearing loss, for example, is damage to the tiny hair cells in our inner ears that vibrate in response to sound waves. These vibrations are then translated by the brain into what we think of as hearing.

Sadly, the same sensitivity of these hair cells that allows them to react to sound waves and translate them into electrical impulses that our brains understand as hearing also makes them fragile, and susceptible to damage. This damage may occur as the result of infections, medications, aging, and by prolonged exposure to loud sounds, resulting in noise-induced hearing loss, or NIHL. The hair cells in human ears can’t be regenerated or “fixed” after they are damaged or destroyed. Instead, hearing specialists and audiologists must use technologies such as hearing aids or cochlear implants to compensate for hearing loss that is essentially irreversible.

This would not be true if humans were more like fish and chickens. Unlike humans, some fish species and birds actually have the ability to regenerate their damaged inner ear hair cells and recover their lost hearing. Bizarre, but true. For reasons that are not fully understood, chickens and zebra fish(to name just 2 such species) have the ability to spontaneously duplicate and replace damaged inner ear hair cells, and thus attain full functional recovery from hearing loss.

Could hearing loss in humans be reversed? Glimmers of hope are appearing from the groundbreaking research of the Hearing Restoration Project (HRP), but the research is at a very early stage and no practical benefits for humans have yet been achieved. This research, funded by the non-profit Hearing Health Foundation, is currently taking place at 14 laboratories in Canada and the United States. Working to identify the molecules that allow the replication and regeneration in some animals, HRP researchers hope to find a way to stimulate human hair cells to do the same.

This work is painstaking and challenging. Researchers need to sort through the many compounds involved in the regeneration process – some of which expedite replication while others hinder it. By figuring out which of the molecules regulate this process in fish or avian cochlea, the researchers are hoping to establish which molecules promote hair cell growth. A few of the HRP researchers are working on gene therapies as a way to stimulate such regrowth, while others are working on stem cell-based approaches.

Although this work is still in it’s preliminary stages, our team wishes them speedy success so that their findings can be extended to humans. Nothing would be more thrilling than to be able to offer our hearing loss patients a true cure.

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