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ANN ARBOR,
MI - If hearing loss runs in your family and the doctor says
it's otosclerosis, it may be important to see a genetic counselor
as well as a surgeon, according to new research from the University
of Michigan Medical School.
Otosclerosis
is a form of progressive conductive hearing loss, which usually
begins in young adulthood. It occurs when a bone in the middle ear
called the stapes becomes immobilized or fixed, which prevents it
from transmitting sound vibrations from the outside world to the
inner ear and brain.
"About
1 percent of Americans have been diagnosed with otosclerosis, but
it may affect up to 10 percent of the total population," says
Marci Lesperance, M.D., an assistant professor of otolaryngology-head
and neck surgery in the U-M Medical School.
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| People
with the genetic mutation often have unusually broad thumbs
and great toes with webbing of tissue between toes as shown
in these photos. |
In recent research,
Lesperance and her colleagues discovered the gene underlying a rare
hearing loss syndrome, called autosomal dominant stapes ankylosis,
which is easily confused with otosclerosis. People with this condition
have the same fixed stapes bones as those with otosclerosis, but
their hearing loss is present at birth and doesn't get worse as
they grow up. People with the syndrome are often farsighted and
have unusually broad thumbs and great toes, as well as other skeletal
abnormalities.
Lesperance
says the syndrome is caused by a genetic mutation occurring early
in embryonic development. Since the mutated gene is dominant over
the normal version, a child has a 50:50 chance of being born with
the syndrome, if one parent carries the mutation.
Comparing DNA
from nine members of one family and three members of another family
with closely related symptoms, U-M researchers found similar mutations
in a gene called NOG. NOG holds genetic instructions
for the production of noggin - an essential protein for normal bone
and joint development in humans and all mammals. One family member
in the study who did not have the syndrome, spouses of family members,
and 100 DNA control samples all had the normal version of the noggin
gene.
"Seven
members of this family were diagnosed with garden-variety otosclerosis
by different physicians," Lesperance said. "The skeletal
anomalies associated with the syndrome can be subtle, and the typical
ENT physician doesn't ask patients to take off their socks, so she
can examine their toes."
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Marci
Lesperance, M.D.
|
David
J. Brown, M.D. |
A surgical
procedure called a stapedectomy is up to 90 to 95 percent successful
in curing otosclerosis, according to David J. Brown, M.D., a U-M
resident who worked closely with the family described in the study
and is first author of the paper. In this procedure, the fixed stapes
bone is removed and a prosthesis is inserted in its place to restore
normal vibration.
"But the
surgery is more difficult and seems to work only for a limited time
in people with the genetic syndrome," Brown says. "So
it's important for clinicians to look for skeletal abnormalities
and ask about a family history of hearing loss and farsightedness
before considering surgery. Hearing aids may be a better option
for people with this syndrome."
"The only
reason this family contacted us was that 8 of 9 family members were
affected," Lesperance says. "There are probably many more
families where only one or two have the syndrome. If two people
in the family have hearing loss and similar physical characteristics,
an evaluation by a geneticist would be appropriate."
Results from
the U-M study will appear in the September 2002 issue of the American
Journal of Human Genetics. The paper was selected for advanced
publication and published electronically on June 27, 2002 on the
American Society of Human Genetics web site at: www.ajhg.org/journal/rapid.html.
In addition
to Brown and Lesperance, collaborators on the study from the U-M
Medical School include: Elizabeth M. Petty, M.D., associate professor
of internal medicine and human genetics; Catherine A. Downs, M.S.,
genetic counselor; Peter J. Strouse, M.D., associate professor of
radiology; Sayoko E. Moroi, M.D., Ph.D., assistant professor of
ophthalmology and visual sciences; Donna M. Martin, Ph.D., research
investigator; Theresa B. Kim, research intern; and Jeff M. Milunsky,
M.D., from the Boston University School of Medicine.
The study was
funded by the Research Fund of the American Otological Society,
the National Institute on Deafness and Other Communication Disorders,
the Margaret G. Bertsch Endowment Fund and the U-M General Clinical
Research Center.
For more information
on inherited hearing loss, please see the following web sites:
www.med.umich.edu/childhearinginfo
http://otosclerosis.khri.med.umich.edu
www.khri.med.umich.edu/research/lesperance_lab/index.htm
Special notes
on this release
U-M scientists
are interested in locating people with a family history of otosclerosis
or other types of hearing loss. If you or a member of your family
has been diagnosed with otosclerosis and are interested in volunteering
for research on genes involved with hearing loss, please register
on this web site: http://otosclerosis.khri.med.umich.edu/
Media Contact:
Sally Pobojewski, pobo@umich.edu
(734) 615-6912 or (734) 764-2220
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