Dr. Sharon Cushing of the Hospital for Sick Children in Toronto explains auditory neuropathy and discusses the outlook for treatment for children diagnosed with hearing loss.
Approximately 10% of children who are diagnosed with hearing loss at birth have auditory neuropathy usually due to genetic structure.
A type of sensorineural hearing loss in which the inner ear successfully detects sound, but is unable to send sound from the ear to the brain.
Researchers report several causes of auditory neuropathy. The most common genetic cause is insufficient production of a protein called otoferlin. The otoferlin protein allows communication between the inner ear sensory cells and the auditory nerve. When the otoferlin protein is deficient, the ear cannot communicate with the nerve and brain. This results in severe to profound hearing loss.
Auditory neuropathy is one of the most challenging forms of hearing loss to diagnose. Over the last two decades, scientists have made substantial progress in identifying genetic causes of hearing loss. Because of these advances, a simple genetic test can now diagnose otoferlin deficiency and other causes of hearing loss.
Some but not all children may benefit from hearing aids, cochlear implants, and other technologies. Gene therapy, guided by an understanding of the complex biology of the inner ear, may hold the key for children whose hearing loss is determined to be caused by an otoferlin deficiency.Learn how hearing works
2A portion of the cochlea known as the organ of Corti contains hair cells that convert this fluid movement into what our brain perceives as sound. There are two types of hair cells. Outer hair cells amplify quiet sounds, while inner hair cells primarily detect and transmit sound signals to the brain via the auditory nerve. There are roughly 3,200 inner hair cells and 12,000 outer hair cells in the human organ of Corti.
3Outer and inner hair cells are arranged linearly within the cochlea tonotopic array. Hair cells at the base of the cochlea detect the highest frequencies. Those located at the apex, or tip, detect the lowest frequencies.
4For normal hearing function, a variety of additional cell types and cellular structures must work together in concert. Broadly speaking, these include (but are not limited to):
- Stereocilia: structures that project from hair cells and respond to movement of fluid within the cochlea, enabling the sensation of sound.
- Synapses: specialized connections that are required for the efficient transfer of sound information from hair cells to spiral ganglion neurons.
- The stria vascularis: a group of cells that produce endolymph, a fluid in the cochlea that moves in response to sound waves.
- Spiral ganglion neurons: cells that transmit information from the cochlea to the brain, where sound is perceived.
Damage or dysfunction within any of these cell types can occur, and lead to symptoms of hearing loss, tinnitus, or hyperacusis.Close
WATCH: DR. SHARON CUSHING OF THE HOSPITAL FOR SICK CHILDREN
LEARN MORE ABOUT HEARING LOSS
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Glossary of Terms
auditory neuropathy: a hearing disorder in which sound enters the inner ear normally, but is impaired when signals move from the inner ear to the brain
cochlear implant: an electronic device that is surgically implanted and works by directly stimulating functioning auditory nerve fibers in the inner ear; cochlear implants convert sound waves to electrical impulses and transmit them to the inner ear, providing people with severe to profound hearing loss the ability to hear sounds
congenital hearing loss: hearing loss that is present at birth
gene therapy: a technique that modifies a person’s genes to treat or cure disease
genetic hearing loss: hearing loss caused by a genetic deficiency or mutation of a gene
otoferlin (OTOF): a large protein expressed in cochlear inner hair cells that enables communication between the sensory cells of the inner ear and the auditory nerve by regulating synaptic transmission
sensorineural hearing loss: hearing loss that occurs from damage to the inner ear, the nerve that runs from the ear to the brain (auditory nerve), or the brain
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