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
- "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.
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
- 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
Daily Health News
Subscribe to MedicineNet's Children's Health & Parenting Newsletter
Top Pendred Syndrome Related Articles
Birth DefectsBirth defects have many causes and currently, are the leading cause of death for infants in the first year of life. Some of the causes of birth defects include genetic or chromosome problems. Exposure of the mother to rubella or German measles during pregnancy, or using drugs or alcohol during pregnancy. The treatment for birth defects depends upon the condition of the effected child.
DeafnessHearing loss (deafness) may be present at birth or it may manifest later in life. Deafness may be genetic or due to damage from noise. Treatment of deafness depends upon its cause. Sensorineural hearing loss can be caused by conditions affecting the:
- eighth cranial nerve,
- spinal cord, or
- Meniere's disease,
- noise-induced hearing loss
- hearing loss of aging (presbycusis),
- nerve injury from syphilis,
- hearing loss of unknown cause (idiopathic hearing loss),
- nerve tumors, and
- drug toxicity (such as aspirin and aminoglycosides).
The definition of a genetic disease is a disorder or condition caused by abnormalities in a person's genome. Some types of genetic inheritance include single inheritance, including cystic fibrosis, sickle cell anemia, Marfan syndrome, and hemochromatosis. Other types of genetic diseases include multifactorial inheritance. Still other types of genetic diseases include chromosome abnormalities (for example, Turner syndrome, and Klinefelter syndrome), and mitochondrial inheritance (for example, epilepsy and dementia).
Hypothyroidism is any state in which thyroid hormone production is below normal. Normally, the rate of thyroid hormone production is controlled by the brain by the pituitary gland. Hypothyroidism is a very common condition and the symptoms of hypothyroidism are often subtle, but may include, constipation, memory loss, hair loss, and depression. There are a variety of causes of hypothyroidism, and treatment depends on the cause.
levothyroxine sodiumLevothyroxine (Synthroid, Levoxyl, Levothroid, Unithroid, Tirosint, Levo-T) is a synthetic version of the principle thyroid hormone, thyroxine (T4), which is made and released by the thyroid gland. Thyroid hormone increases the metabolic rate of cells of all tissues in the body. It is prescribed to treat hypothyroidism and to suppress thyroid hormone release in the management of cancerous thyroid nodules and growth of goiters. It is important to be aware of drug interactions, as well as common side effects on the user.
MRI ScanMRI (or magnetic resonance imaging) scan is a radiology technique which uses magnetism, radio waves, and a computer to produce images of body structures. MRI scanning is painless and does not involve X-ray radiation. Patients with heart pacemakers, metal implants, or metal chips or clips in or around the eyes cannot be scanned with MRI because of the effect of the magnet.
Sign LanguageAmerican Sign Language (ASL) is a complete, complex language that employs signs made with the hands and other movements, including facial expressions and postures of the body. No one form of sign language is universal. For example, British Sign Language (BSL) differs notably from ASL. Different sign languages are used in different countries or regions.