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Hearinginfo.org
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Current Research on Hearing Disorders |  |
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Cochlear
Implants, Genetics of Hearing |
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Federally Funded Research
on Cochlear Implants, Genetics of Hearing
Loss, Hair Cell Generation. Funded by the NIDCD, an NIH Department.***
Mutation in Gene for Protein Radixin Causes Hearing Loss in Humans
Radixin is an important protein that makes up the hair-like bundles on
top of sensory cells in the inner ear. Mutations of the gene RDX,
which encodes radixin, have been found to cause deafness in mice. In
this study, NIDCD researchers show evidence that two Pakistani
families with mutations in the RDX gene also exhibit hearing loss that
is not associated with other symptoms. The findings are published in
the Jan. 16, 2007, issue of Human Mutation. Title: Mutations of the
RDX Gene Cause Nonsyndromic Hearing Loss at the DFNB24 Locus (poster);
Principal investigator: Thomas Friedman, Ph.D., NIDCD.
Mutation that Causes Muenke Syndrome
Severely Disrupts Inner Ear
Development in Mice
Muenke syndrome, a rare disorder that includes symptoms such as an
abnormally shaped skull, dwarfism, and hearing loss, is caused by a
mutation in the gene that encodes the protein Fgfr3. Fgfr3 is a
receptor for fibroblast growth factors, a protein family that signals
nearby cells and kick-starts activities that play a key role in
embryonic development and growth, including the development of hearing
structures. In this study, researchers show that mice missing the
Fgfr3 gene exhibit a broad range of hearing abnormalities, indicating
that Fgfr3 regulates many developmental processes in the inner ear.
Title: Disruption of Fgfr3 Signaling Results in Defects in Cellular
Differentiation, Neuronal Patterning, and Hearing Impairment (poster);
Principal investigator: Matthew Kelley, Ph.D., NIDCD.
Signaling Proteins Help Ear's Sensory Cells "Know" Where to Grow
The process by which an embryo develops the highly-specialized
structures necessary for hearing is still a mystery to scientists. A
cascade of reactions, kicked off by "signaling" proteins, is critical
in directing the activities of an embryo's ' dividing cells. One such
family, the Wnt proteins, is of particular importance in initiating
reactions in a developing organism, and a disruption of these
reactions - caused by a mutation to one or more Wnt genes - can result
in developmental defects, diseases, and cancer. NIDCD researchers
describe how activities of three Wnt proteins help determine the
precise location and orientation of key sensory cells in the inner
ear. Title: Wnt Signaling in the Mammalian Cochlea (symposium
session); Principal investigator: Matthew Kelley, Ph.D., NIDCD.
Form of Cadherin 23 Linked to Deafness in Mouse Model Identified
Cadherin 23 is a large protein that composes sensory structures in
both the inner ear and retina. Researchers have yet to understand why
some mutations to the gene that encodes it, CDH23, cause only deafness
while other mutations cause deafness, blindness, and balance problems,
as in Usher syndrome type 1. Cadherin 23 also comes in a variety of
forms that may be expressed differently in the retina and inner ear.
NIDCD researchers examined cadherin 23's various forms and found only
one form to be expressed in the cochlea of a mouse model, suggesting
that the loss of function of this form is responsible for the mouse's
deafness. Title: Cadherin 23 Alternative Splice Variants: Studying the
Molecular Basis of Waltzer (poster); Principal investigator: Thomas
Friedman, Ph.D., NIDCD.
'Motor'-Protein-Containing Particles Help Rev Up Our Hearing
Scientists are exploring how tiny sensory structures in our inner
ears, called hair cells, are sensitive to faint sounds. Although all
hair cells help convert sound vibrations to electrical signals, inner
hair cells relay those signals to the brain, while outer hair cells
are thought to play a role in amplifying those signals. With the aid
of an atomic force microscope, NIDCD researchers have found that tiny
particles packed inside the cell membrane of the outer hair cell are
composed of prestin, a 'motor' protein known for causing a cell to
change shape in response to an electrical signal. The findings
indicate that the membrane particles play a direct role in the
expansion and contraction of outer hair cells in response to
electrical signals and, most likely, the strengthening of those
signals. Title: Evidence for Prestin in 10 nm Particles in the Lateral
Membrane Of Outer Hair Cells: an Atomic Force Microscopic Study
(podium session); Principal investigator: Kuni Iwasa, Ph.D., NIDCD.
Research conducted by NIDCD-funded
scientists include:
Are Two Cochlear Implants Better Than One?
More and more often, children with profound hearing loss are being
fitted with two cochlear implants - one for each ear - in hopes that
the child may better home in on a sound's source and gain a more
realistic listening experience. In this NIDCD-supported study,
researchers assess the sound-localization abilities of children (ages
5 to 14 years) wearing two cochlear implants in comparison to one. The
researchers found that most of the children in the study located the
source of a sound more accurately when they were wearing two implants
as opposed to one. In addition, the team found that improvement in
localization was seen only when the child used two implants, but not
when a single implant was used; also, the more experienced the child
was with two implants, the more adept he or she became at localizing
sound. Litovsky's research team is now investigating the effects of
bilateral implants on word learning and language acquisition in young-
implanted infants and toddlers. Title: Emergence of Localization
Abilities in Children with Sequential Bilateral Cochlear Implants
(podium session); Principal investigator: Ruth Litovsky, Ph.D.,
University of Wisconsin.
Inner Ear Stem Cells May Help Rewire Hearing
When hair cells are destroyed - by disease, injury, or aging - the
attached nerve cells, or neurons, that relay electrical signals to the
brain are often destroyed as well. In this NIDCD-funded study,
scientists demonstrate that stem cells from the inner ear of a mouse
can be grown into new neurons. Moreover, these neurons can form new
connections with hair cells and carry electrical signals. The findings
may one day be used in combination with other potential technologies
for the treatment of hearing loss, such as hair cell regeneration and
more advanced cochlear implants.Title: Neurons Derived from Inner Ear
Stem Cells Form Synapses with De-Afferented Hair Cells (poster);
Principal investigator: Albert Edge, Ph.D., Harvard Medical School.
Restoring the Sixth Sense
Scientists are currently working to develop an implant for some people
who lose their sense of balance. Just as the cochlear implant converts
sound to electrical signals that stimulate the auditory nerve, a
vestibular implant converts movements of the head into signals that
stimulate the vestibular nerve. Although this technology is still in
the early stages of development, two NIDCD-funded studies describe
recent progress. The first study describes a model that predicts
current flow for different electrode designs and a second study
describes adjustments that would reduce power consumption of an
implant in humans. Titles:1)An Anatomically Precise Finite Element
Model Predicts Current Flow in Labyrinths Implanted with a Multi-
Channel Vestibular Prosthesis (poster) and 2)Paired Linear
Accelerometers Emulate Gyros to Reduce Power Consumption and Size for
an Implantable Multi-Channel Vestibular Prosthesis (poster); Principal
investigator: Charles C. Della Santina, M.D., Ph.D., Johns Hopkins
School of Medicine.
New Tool Helps Scientists Tinker with the Ear's 'Motor'
NIDCD-supported researchers have developed a computer model to study
how outer hair cells, sensory structures in the inner ear, help us to
hear. Hair cells convert sound vibrations into electrical signals that
are relayed to the brain. The membrane of the outer hair cell can act
as a "motor" that amplifies inner ear vibrations and improves the
electrical signal by causing the cell to lengthen and contract. If
this membrane motor doesn't function, hearing loss results. The
computer model simulates the stretching of a cell membrane, a lab
technique researchers use to study a membrane's properties. By
observing the membrane in more vivid detail, scientists will better
understand the membrane-lodged motor that allows us to hear. Title:
Modeling Membrane-Cytoskeleton Interaction in the Cochlear Outer Hair
Cell Tether Pulling Experiment (poster); Principal investigator:
William Brownell, Ph.D., Baylor College of Medicine.
For more information about the Association for Research in
Otolaryngology, visit their Web site at www.aro.org. (http://
www.aro.org.)
***The National Institutes of Health (NIH)
- The Nation's Medical
Research Agency - includes 27 Institutes and Centers and is a
component of the U.S. Department of Health and Human Services. It is
the primary federal agency for conducting and supporting basic,
clinical and translational medical research, and it investigates the
causes, treatments, and cures for both common and rare diseases. For
more information about NIH and its programs, visit
www.nih.gov.
(http://www.nih.gov.)