Stories about: otolaryngology

Gene therapy restores whisper-fine hearing, balance in Usher syndrome mice

gene therapy for deafness
Sensory hair cells contain tiny cilia that get wiggled by incoming sound waves, sparking a signal to the brain that ultimately translates to hearing. Gene therapy restored this tidy “V” formation. (Credit: Gwenaelle Géléoc and Artur Indzkykulian)

The ear is a part of the body that’s readily accessible to gene therapy: You can inject a gene delivery vector (typically a harmless virus) and it has a good chance of staying put. But will it ferry the corrected gene into the cells of the hearing and/or vestibular organs where it’s most needed?

Back in 2015, a Boston Children’s Hospital/Harvard Medical School team reported using gene therapy to restore rudimentary hearing in mice with genetic deafness. Previously unresponsive mice began jumping when exposed to abrupt loud sounds. But the vector used could get the corrected genes only into the cochlea’s inner hair cells. To really restore significant hearing, the outer hair cells need to be treated too.

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An iPhone and a bucket help diagnose vestibular problems in dizzy children

dizziness vestibular bucket testDizziness is fairly common in children, but it can be very hard to diagnose the cause. Any number of conditions can produce dizziness, and children are a special challenge since they often can’t describe what they’re feeling.

“One of the toughest things to figure out is, is it a problem with the vestibular system, or is it part of something else, a heart problem or an eye problem?” says Jacob Brodsky, MD, director of the Balance and Vestibular Program at Boston Children’s Hospital. “Then, the next challenging part is determining whether it is an inner ear problem or a central vestibular disorder — a problem with the brain.”

A definitive answer often requires a battery of tests that few providers outside Boston Children’s can perform in children, as they require sophisticated and expensive equipment. But with an ordinary bucket, an iPhone, an $18 app and some Velcro, Brodsky can quickly get a good indication of whether a child has a vestibular problem—and specifically an inner ear problem.

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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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