What is Pendred syndrome?
Pendred syndrome is a genetic disorder that causes early hearing loss
in children. It also can affect the thyroid gland and sometimes may affect a
person’s balance. The syndrome is named after Vaughan Pendred, the physician who
first described individuals with the disorder.
Children who are born with Pendred syndrome may begin to
lose their hearing at birth or by the time they are three years old. The hearing
loss is progressive, which means that a child will have less hearing over time. Some
individuals may become totally deaf.
The loss of hearing often happens suddenly and in
stages. Sometimes, after a sudden decrease in hearing, a person’s hearing will
nearly return to its previous level. Almost all people with Pendred syndrome
have bilateral hearing loss, or hearing loss in both ears. The hearing loss
often is greater in one ear
than in the other.
How does Pendred syndrome affect other parts of the body?
Pendred syndrome can affect the thyroid by causing it to
grow too large. An enlarged thyroid gland also is called a goiter. The thyroid is
a small, butterfly-shaped gland in the front of your neck, just above your collarbones. The thyroid plays a major
role in how your body uses energy from food. In children, the thyroid is
important for normal growth and development. Children with Pendred syndrome,
however, rarely have problems growing and developing properly even if their
thyroid is affected.
Roughly 60 percent of individuals with Pendred syndrome will develop a goiter
in their lifetime. Most people with Pendred syndrome are in their teens or
twenties before they develop a goiter. If a goiter becomes large, a person may
have problems breathing and swallowing. A health professional is needed to check
a person’s goiter over time and decide what treatment is necessary.
Pendred syndrome also may affect the vestibular system,
which controls balance. About 40 percent of individuals with Pendred syndrome
will show some vestibular weakness when their balance system is tested. However,
the brain is
very good at making up for a weak vestibular system, and most children and
adults with Pendred syndrome do not have a problem with their balance or have
difficulty doing routine tasks. Some babies with Pendred syndrome may start
walking later than other babies.
It is not known why some individuals with Pendred syndrome develop a goiter
or have balance problems and others do not.
What causes Pendred syndrome?
Pendred syndrome can be caused by changes, or
mutations, to a gene known as SLC26A4 (also referred to as the PDS gene) on
chromosome 7. Because it is a recessive trait, a child needs to inherit two
mutated SLC26A4 genes—one from each parent—to have Pendred syndrome. The child’s
parents do not need to have Pendred syndrome to be a carrier of a mutation in
the SLC26A4 gene.
Couples who are concerned that they might be able to pass Pendred syndrome on
to their children may seek genetic testing. A possible sign that a person may be
a carrier of a mutated SLC26A4 gene is a family history of early hearing loss.
Another sign is a family member who has both a goiter and hearing loss. A
mutation in the SLC26A4 gene can be determined by genetic testing that uses a
blood sample.
The decision to have a genetic test is complex. Most people receive
assistance from a genetic counselor trained to help them weigh the medical,
emotional, and ethical considerations. A genetic counselor is a health
professional who provides information and support to individuals and families
who have a genetic disease or who are at risk for such a disease.
How is Pendred syndrome diagnosed?
A physician called an otolaryngologist or a
clinical geneticist will consider a person’s hearing, inner ear structures, and
sometimes the thyroid in diagnosing Pendred syndrome. The specialist will
evaluate the timing, amount, and pattern of hearing loss. He or she will ask
questions such as:
- "When did the hearing loss start?,"
- “Has it worsened over
time?,” and - “Did it happen suddenly or in stages?.”
Early hearing loss is one of
the most common characteristics of Pendred syndrome; however, this symptom alone
does not mean a child has the condition.
The specialist uses inner ear imaging techniques known
as magnetic resonance imaging (MRI) or computed tomography (CT or CAT) to look for two key
characteristics of Pendred syndrome. One characteristic might be a cochlea with
too few turns. The cochlea is the spiral-shaped part of the inner ear that
converts sound into electrical signals that are sent to the brain. A healthy
cochlea has two-and-a-half turns, but the cochlea of a person with Pendred
syndrome may have only one-and-a-half turns.
A second characteristic of Pendred syndrome is enlarged
vestibular aqueducts (see figure). The vestibular aqueduct is a bony canal that
runs from the vestibule (a part of the inner ear between the cochlea and the
semicircular canals) to the inside of the skull. Inside the vestibular aqueduct
is a fluid-filled tube called the endolymphatic duct, which ends at a balloon-shaped
endolymphatic sac. When the vestibular aqueduct is enlarged, the endolymphatic
duct and sac grow large with excess fluid in comparison to their normal sizes.
The function of the vestibular aqueduct is not well understood.
Picture of the Inner Ear
When screening for Pendred syndrome, it is not recommended to test the blood
for thyroid hormone because the amount usually is the same whether someone has
Pendred syndrome or not. Some people may receive a “perchlorate washout test,” a
test that determines whether the thyroid is functioning properly. Although this
test is probably the best test for determining thyroid function in Pendred
syndrome, it is not used often and may be replaced by genetic testing.
Individuals who have a goiter may be referred to an endocrinologist, a doctor
who specializes in glandular disorders, to determine whether the goiter is due
to Pendred syndrome or to another cause. Goiter is a common feature of Pendred
syndrome, but many individuals who develop a goiter do not have Pendred
syndrome. Conversely, many people who have Pendred syndrome never develop a
goiter.
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How common is Pendred syndrome?
Scientists estimate that about two to three
children out of every 1,000 have early hearing loss, and about half of these
cases are inherited. The SLC26A4 gene, which causes Pendred syndrome, accounts
for about five to ten percent of hereditary hearing loss. As researchers gain
more insight about the syndrome and its features, they hope to improve doctors’
ability to detect and diagnose the disorder in people.
Can Pendred syndrome be treated?
Treatment options are available for individuals with
Pendred syndrome. Because the syndrome is inherited and can involve thyroid and
balance problems, many specialists may be involved in treatment. The treatment
team may include a primary care physician, an
audiologist, an endocrinologist, a clinical geneticist, a genetic counselor, an
otolaryngologist, and a speech-language pathologist.
To reduce the likelihood of progression of hearing loss,
individuals with Pendred syndrome should:
- avoid contact sports that might lead to
head injury; - wear head protection when engaged in activities that might lead to head injury
(such as bicycle riding or skiing); and - avoid situations that can lead to
barotrauma (extreme,
rapid changes in pressure), such as scuba diving or hyperbaric oxygen treatment.
Pendred syndrome cannot be cured. However, the medical team can help parents
and individuals make informed choices about treatment options. They also can
help them prepare for increased hearing loss and other possible long-term
consequences of the syndrome.
Children with Pendred syndrome should start early treatment to learn skills
that will help them communicate, such as learning sign language or cued speech
or how to use a hearing aid. Most
individuals with Pendred syndrome will have hearing loss significant enough to
be considered eligible for a cochlear implant. A cochlear implant is an
electronic device that is surgically inserted into the cochlea. A cochlear
implant does not restore or create normal hearing. Instead, a cochlear implant
helps a person develop a new way of understanding speech. Children over 12
months of age as well
as adults are eligible to receive an implant.
Individuals with Pendred syndrome who develop a goiter need to have it
checked regularly. The goiter in Pendred syndrome is unusual because the thyroid
is making the right amount of thyroid hormone but it is growing in size. Such a
goiter often is called a euthyroid
goiter.
What research is being conducted?
NIDCD has been working to understand
hearing loss caused by inherited syndromes such as Pendred syndrome as well as
from other causes. Researchers also are looking carefully at the characteristics
of the disorder and how the syndrome might cause problems in such different
parts of the body as the thyroid and inner ear.
Scientists continue to study the genetic basis of
Pendred syndrome. The protein that the SLC26A4 gene encodes, called pendrin, is found in the inner
ear, kidney, and thyroid gland. Researchers have identified more than 90
deafness-causing mutations or alterations of this gene.
Scientists have altered the gene in mice so that the
mice have an abnormal SLC26A4 gene. The study of these mice is providing
information on how the abnormal gene affects the form and function of different
parts of the body. For example, by studying the inner ears of mice with SLC26A4
mutations, scientists now realize that the enlarged vestibular aqueduct
associated with Pendred syndrome is not caused by a sudden stop in the normal
development of the ear. Studies such as this are important because they help
scientists rule out some
causes of a disorder while helping to identify areas needing more research.
Eventually, researchers are hopeful that these studies will lead to therapies
that can target the basic causes of the condition.
SOURCE: National Institute on Deafness and
Other Communication Disorders, National Institutes of Health