CONTACT: JENNIFER BROWN
Iowa City IA 52242
(319) 335-9917; fax(319) 384-4638
Release: Sept 30, 2002
Fast-paced gene discovery changes clinical practice for care of deaf patients
In 1997, researchers first identified a genetic cause of non-syndromic deafness
-- hearing loss that is the patient's only abnormality. Since then, the number
of genes known to cause non-syndromic deafness has risen to 29. The rapid
pace of discovery has generated great excitement among genetics researchers,
and has changed the way physicians diagnose hereditary deafness.
Genetic testing is now becoming a component of clinical care for deaf children
and their families. At University of Iowa Health Care, clinicians in the Division
of Pediatric Otolaryngology, in conjunction with the Molecular Otolaryngology
Research Laboratories, provide genetic testing for 800 families each year.
Results of genetic tests can provide helpful diagnostic and prognosis information
to these families.
Prior to 1997, in most instances, the only way to diagnose non-syndromic
genetic deafness was to exclude all other possible causes of deafness, said
Richard Smith, M.D., the Sterba Hearing Research Professor at UI Roy J. and
Lucille A. Carver College of Medicine, and director of the Molecular Otolaryngology
"Typically, a physician would order a large battery of tests to determine
if the mother had been exposed to an illness during pregnancy that caused
the baby's deafness," said Smith, who recently was part of a research
team that identified a new gene which when mutated can cause deafness. "Now,
we don't need to order numerous tests because we know that 50 percent of congenital
non-syndromic deafness is due to mutations in a single gene called GJB2. This
single finding has changed the practice of clinical medicine."
GJB2-related hearing loss is considered a recessive genetic disorder because
the mutations only cause deafness in individuals who inherit two copies of
the mutated gene, one from each parent. A person with one mutated copy and
one normal copy is a carrier but is not deaf.
In Iowa, 90 percent of newborns are tested for hearing. A probe placed in
the baby's ear canals generates sound, and electrodes placed on the baby's
head record brain responses to the sound. If this test indicates that a baby
is deaf or hearing impaired, the newly available genetic tests may be able
to pinpoint an exact genetic cause of the deafness. The Molecular Otolaryngology
Research Laboratories at the UI offers mutation screening of three genes known
to cause hearing loss, including GJB2.
Many deafness-causing mutations can occur in the GJB2 gene, but one particular
mutation is most prevalent in people of Northern European decent, a group
that includes most Iowans.
"This mutation arose as a result of a founder effect -- one person has
the mutation and passes it on to all of their progeny," Smith said. "This
particular founder effect occurred approximately 8,000 years ago, and one
in every 40 people in the Midwestern United States is related to that common
Just as genetic testing has become part of diagnosing causes of deafness,
so genetic counseling also has assumed an increasingly important role in the
treatment of deaf patients and their families.
Smith explained that many parents find genetic diagnosis and the accompanying
genetic counseling beneficial. They are reassured by the information and the
by the knowledge of a specific cause of their child's deafness.
Genetic tests and counseling also can give patients and parents information
about the likely progression of a child's hearing impairment
"We know that over the long term, deafness caused by mutations in GJB2
does not generally worsen. A child who has moderate-to-severe deafness caused
by GJB2 mutations will have the same level of deafness at ages 10 and 20,"
Smith said. "That means that if the child is doing well with traditional
amplification (hearing aid), they don't necessarily have to worry about further
deterioration of hearing."
Current genetic tests have helped improve patient care; however, they do
have limitations and subtleties that need to be recognized by health care
providers and patients alike. Whereas a positive result establishes with certainty
the cause of deafness and also can quantify the likelihood of deafness in
future offspring, a negative test does not definitively prove that the deafness
is not genetic.
Also, unlike many other medical tests, results of an individual's genetic
test have direct implications for other family members. If a child of hearing
parents has GJB2-related deafness, it means that both parent are carriers
and the child's hearing siblings have a two-thirds chance of being carriers.
Carrier-testing is not recommended for children because carrying one mutated
copy of the gene does not cause deafness and therefore has no effect on the
child's life. However, the ability to test for susceptibility genes raises
the larger question of whether relatives should be told the results of an
individual's genetic test or whether those results should remain private as
is usually the case with medical information.
Smith also notes that while hearing parents of a deaf child might seek treatment
such as hearing aids and cochlear implants, the situation may be different
for deaf parents of a deaf child. People who are born deaf and identify themselves
with the Deaf community consider deafness an integral part of their culture,
and their language (sign language) is simply another language like English
or French. The Deaf community does not believe that deafness is something
to be treated.
Therefore, it is important that genetic testing and genetic counseling be
provided in the context of each patient's wishes and needs, Smith said.
As genetic testing becomes a routine part of clinical practice, physicians
will be required to be more familiar with genetic testing and its limitations,
and also to understand which patients are good candidates for testing.
"These issues are bigger than hereditary deafness; they apply to physicians
irrespective of their specialty," Smith said. "The tremendous advances
we are making right now in the field of genetics in all realms of medicine
will be a driving force for clinicians to become geneticists, so that they
can provide their patients with better care."
University of Iowa Health Care describes the partnership between
the UI Roy J. and Lucille A. Carver College of Medicine and UI Hospitals and
Clinics and the patient care, medical education and research programs and
services they provide. Visit UI Health Care online at www.uihealthcare.com.