Stories about: hearing loss

Gene therapy restores hearing in deaf mice

A closeup of the sensory hair bundles in the cochlea (inverted v's), each containing 50 to 100 microvilli tipped with TMC proteins. Cell bodies are below the bundles. (Gwenaelle S. Geleoc & Artur A. Indzhykulian)
The inverted V’s above are sensory hair bundles in the ear, each containing 50 to 100 microvilli tipped with TMC proteins. Gene therapy restores hearing by providing working copies of those proteins. (Gwenaelle Geleoc & Artur Indzhykulian)

More than 70 different genes are known to cause deafness when mutated. Jeffrey Holt, PhD, envisions a day when patients with hearing loss have their genome sequenced and their hearing restored by gene therapy. A proof-of-principle study published today by the journal Science Translational Medicine takes a clear step in that direction, restoring hearing in deaf mice.

“Our gene therapy protocol is not yet ready for clinical trials—we need to tweak it a bit more—but in the not-too-distant future we think it could be developed for therapeutic use in humans,” says Holt, a scientist in the F.M. Kirby Neurobiology Center at Boston Children’s Hospital and an associate professor of Otolaryngology at Harvard Medical School.

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Hearing restoration has a sound future

Ear-engraved styleThis post is adapted from a commentary in this week’s edition of Science by Jeffrey R. Holt, PhD, and Gwenaelle S. G. Géléoc, PhD, of the Department of Otolaryngology and F.M. Kirby Neurobiology Center at Boston Children’s Hospital.

Hearing loss affects more than 300 million people worldwide, making it the most common sensory disorder. While there are no cures, recent efforts to develop biological treatments for hearing loss provide reason for cautious optimism. Three strategies—gene therapy, stem cells and drugs—have shown encouraging results in animal models, poising them for translation into potential therapies for humans.

Hearing loss can arise from many different causes, so it is unlikely that a single “magic bullet” will be developed to treat all forms of deafness. Rather, each individual cause may require a tailored and specific treatment strategy.

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How things work: Scientists find cellular channels vital for hearing

A mechanosensory hair bundle in the cochlea. Each sensory cell, of which the human ear has about 16,000, has tiny hairs tipped with TMC1 and TMC2 proteins. When sound vibrations strike the bundle, it wiggles back and forth, opening and closing the TMC channels. When open, the channel allows calcium into the cell, initiating an electrical signal to the brain relayed by the 8th cranial nerve. (Image: Yoshiyuki Kawashima)
A mechanosensory hair bundle in the cochlea. Each sensory cell, of which the human ear has about 16,000, has tiny hairs tipped with TMC1 and TMC2 proteins. When sound vibrations strike the bundle, it wiggles back and forth, opening and closing the TMC channels. When open, the channel allows calcium into the cell, initiating an electrical signal to the brain relayed by the 8th cranial nerve. (Image: Yoshiyuki Kawashima)
Ending a 30-year search by scientists, researchers have identified two proteins in the inner ear that are critical for hearing, which, when damaged by genetic mutations, cause a form of delayed, progressive hearing loss.

The proteins are essentially transducers: They form channels that convert mechanical sound waves entering the inner ear into electrical signals that talk to the brain. Corresponding channels for each of the other senses were identified years ago, but the sensory transduction channel for both hearing and the sense of balance had been unknown.

The channels are the product of two related genes known as TMC1 and TMC2. TMC1 mutations were first reported in people with a prominent form of hereditary deafness back in 2002 by Andrew Griffith, MD, PhD, of the National Institute on Deafness and Other Communication Disorders (NIDCD) and collaborators. Children with recessive mutations in TMC1 are completely deaf at birth.

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Gene-therapy trial will attempt to restore hearing in deaf mice

(Molly G. Willikers/Flickr)

Sound waves produce the sensation of hearing by vibrating hair-like structures on the inner ear’s sensory hair cells. But how this mechanical motion gets converted into electrical signals that go to our brains has long been a mystery.

Scientists have believed some undiscovered protein is involved. Such proteins have been identified for taste, smell and sight, but the protein required for hearing has been elusive. In part, that’s because it’s hard to get enough cells from the inner ear to study – they’re embedded deep in the cochlea.

“People have been looking for more than 30 years,” says Jeffrey Holt of the department of otolaryngology at Children’s Hospital Boston. “Five or six possibilities have come up, but didn’t pan out.”

Last week, in the Journal of Clinical Investigation, team led by Holt and Andrew Griffith, of the National Institute on Deafness and Other Communication Disorders (NIDCD), demonstrated that two related proteins, TMC1 and TMC2, are essential for normal hearing – paving the way for a test of gene therapy to reverse a type of genetic deafness. 

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