Causes of Hearing Loss
- What is presbycusis?
Presbycusis is the loss of hearing that gradually occurs in most individuals as they grow
older. Hearing loss is a common disorder associated with aging. About 30-35 percent
of adults between the ages of 65 and 75 years have a hearing loss. It is estimated that
40-50 percent of people 75 and older have a hearing loss. The loss associated with
presbycusis is usually greater for high-pitched sounds. For example, it may be difficult
for someone to hear the nearby chirping of a bird or the ringing of a telephone. However,
the same person may be able to clearly hear the low-pitched sound of a truck rumbling
down the street.
There are many causes of presbycusis. Most commonly, it arises from changes in the
inner ear of a person as he or she ages, but presbycusis can also result from complex
changes along the nerve pathways leading to the brain. Presbycusis most often occurs
in both ears, affecting them equally. Because the process of loss is gradual, people who
have presbycusis may not realize that their hearing is diminishing.
- What are the symptoms of presbycusis?
With presbycusis, sounds often seem less clear and lower in volume. This contributes to difficulty hearing and understanding speech. Individuals with presbycusis may experience several of the following:
- The speech of others seems mumbled or slurred.
- High-pitched sounds such as “s” and “th” are difficult to hear and tell apart.
- Conversations are difficult to understand, especially when there is background noise.
- A man’s voice is easier to hear than the higher pitches of a woman’s voice.
- Certain sounds seem annoying or overly loud.
- Tinnitus (a ringing, roaring, or hissing sound in one or both ears) may also occur.
- What are the causes of presbycusis?
Sensorineural hearing loss is caused by disorders of the inner ear or auditory nerve. Presbycusis is usually a sensorineural hearing disorder. It is most commonly caused by gradual changes in the inner ear. The cumulative effects of repeated exposure to daily traffic sounds or construction work, noisy offices, equipment that produces noise, and loud music can cause sensorineural hearing loss. Sensorineural hearing loss is most often due to a loss of hair cells (nerve endings in the inner ear). This can occur as a result of hereditary factors as well as aging, various health conditions, and side effects of some medicines (aspirin and certain antibiotics).
Presbycusis may be caused by changes in the blood supply to the ear because of heart disease, high blood pressure, vascular (pertaining to blood vessels) conditions caused by diabetes, or other circulatory problems. The loss may be mild, moderate, or severe.
- What can be done?
There are many strategies to help people with presbycusis. Hearing aids may be recommended for some individuals. Assistive listening devices can provide further improvement in hearing ability in certain situations. One example of such a device is the built-in telephone amplifier. Another example is FM systems that make sounds clearer, with or without a hearing aid, by delivering sound waves like a radio. Training in speechreading (using visual cues to determine what is being spoken) can help those with presbycusis to understand better what is being said in conversations or presentations.
- What is Auditory Neuropathy Spectrum Disorder?
Auditory neuropathy spectrum disorder (ANSD) is a hearing disorder in which sound enters the inner ear normally but the transmission of signals from the inner ear to the brain is impaired. It can affect people of all ages, from infancy through adulthood. The number of people affected by auditory neuropathy is not known, but the condition affects a relatively small percentage of people who have hearing loss.
People with ANSD may detect sound at normal levels, or have a hearing loss ranging from mild to severe. What makes this hearing disorder challenging is the individuals have trouble understanding speech clearly, despite having the ability to detect it. In other words, speech perception ability is worse than would be predicted by the degree of hearing loss. For example, a person with ANSD may be able to hear sounds, but would still have difficulty recognizing spoken words.
- What causes ANSD?
Although Auditory neuropathy spectrum disorder (ANSD) is not yet fully understood, scientists believe the condition probably has more than one cause. In some cases, it may involve damage to the inner hair cells—specialized sensory cells in the inner ear that transmit information about sounds through the nervous system to the brain. Other causes may include faulty connections between the inner hair cells and the nerve leading from the inner ear to the brain, or damage to the nerve itself. A combination of these problems may occur in some cases. Although outer hair cells—hair cells adjacent to and more numerous than the inner hair cells—are generally more prone to damage than inner hair cells, outer hair cells seem to function normally in people with ANSD.
- What are the roles of the outer and inner hair cells?
Outer hair cells help amplify sound vibrations entering the inner ear from the middle ear. When hearing is working normally, the inner hair cells convert these vibrations into electrical signals that travel as nerve impulses to the brain, where the impulses are interpreted as sound.
- Are there risk factors for ANSD?
Several factors have been linked to ANSD in children. However, a clear cause and effect relationship has not been proven. Some children who have been diagnosed with ANSD experienced certain health problems as newborns, or during or shortly before birth. These problems include jaundice, premature birth, low birth weight, and an inadequate supply of oxygen to the unborn baby. In addition, some drugs that have been used to treat medical complications in pregnant women or newborns may damage the inner hair cells in the baby’s ears, causing auditory neuropathy.
Some people with ANSD have neurological disorders that also cause problems outside of the hearing system. Examples of such disorders are Charcot-Marie-Tooth syndrome and Friedreich’s ataxia.
- How is ANSD diagnosed?
Health professionals, including otolaryngologists (ear, nose, and throat doctors), pediatricians, and audiologists, use a combination of methods to diagnose ANSD. These include tests of auditory brainstem response (ABR) and otoacoustic emissions (OAE). The hallmark of auditory neuropathy is a negligible or very abnormal ABR reading together with a normal hair cell function either through an OAE or cochlear microphonic measurement from the ABR.
An ABR measures brain wave activity in response to sound using electrodes that are placed on the person’s head and ears. An OAE test uses a small, very sensitive microphone inserted into the ear canal to monitor the faint sounds produced by the outer hair cells in response to stimulation by a series of clicks. ABR and OAE testing are painless and can be used for newborn babies and infants as well as older children and adults. Other tests may also be used as part of a more comprehensive evaluation of an individual’s hearing and speech-perception abilities.
- What is auditory processing?
Auditory processing is a term used to describe what happens when your brain recognizes and interprets the sounds around you. Humans hear when energy that we recognize as sound travels through the ear and is changed into electrical information that can be interpreted by the brain. The “disorder” part of auditory processing disorder means that something is adversely affecting the processing or interpretation of the information.
Children with Auditory Processing Disorder (APD) often do not recognize subtle differences between sounds in words, even though the sounds themselves are loud and clear. For example, the request “Tell me how a chair and a couch are alike” may sound to a child with APD like “Tell me how a couch and a chair are alike.” It can even be understood by the child as “Tell me how a cow and a hair are alike.” These kinds of problems are more likely to occur when a person with APD is in a noisy environment or when he or she is listening to complex information.
APD goes by many other names. Sometimes it is referred to as central auditory processing disorder (CAPD). Other common names are auditory perception problem, auditory comprehension deﬁcit, central auditory dysfunction, central deafness, and
so-called “word deafness.”
- What causes auditory processing difficulty?
We are not sure. Human communication relies on taking in complicated perceptual information from the outside world through the senses, such as hearing, and interpreting that information in a meaningful way. Human communication also requires certain mental abilities, such as attention and memory. Scientists still do not understand exactly how all of these processes work and interact or how they malfunction in cases of communication disorders. Even though your child seems to “hear normally,” he or she may have difﬁculty using those sounds for speech and language comprehension.
The cause of APD is often unknown. In children, auditory processing difﬁculty may be associated with conditions such as dyslexia, attention deﬁcit disorder, autism, autism spectrum disorder, speciﬁc language impairment, pervasive developmental disorder, or developmental delay. Sometimes this term has been misapplied to children who have no hearing or language disorder but have challenges in learning.
- What are the symptoms of possible auditory processing difficulty?
Children with auditory processing difﬁculty typically have normal hearing and intelligence. However, they have also been observed to:
- Have trouble paying attention to and remembering information presented orally
- Have problems carrying out multistep directions
- Have poor listening skills
- Need more time to process information
- Have low academic performance
- Have behavior problems
- Have language difﬁculty (e.g., they confuse syllable sequences and have problems developing vocabulary and understanding language)
- Have difﬁculty with reading, comprehension, spelling, and vocabulary
- How is suspected auditory processing difficulty diagnosed in children?
You, a teacher, or a day care provider may be the ﬁrst person to notice symptoms of auditory processing difﬁculty in your child. So talking to your child’s teacher about school or preschool performance is a good idea. Many health professionals can also diagnose APD in your child. There may need to be ongoing observation with the professionals involved.
Much of what will be done by these professionals will be to rule out other problems. A pediatrician or a family doctor can help rule out possible diseases that can cause some of these same symptoms. He or she will also measure growth and development. If there is a disease or disorder related to hearing, you may be referred to an otolaryngologist—a physician who specializes in diseases and disorders of the head and neck.
To determine whether your child has a hearing function problem, an audiologic evaluation is necessary. An audiologist will give tests that can determine the softest sounds and words a person can hear and other tests to see how well people can recognize sounds in words and sentences. For example, for one task, the audiologist might have your child listen to different numbers or words in the right and the left ear at the same time. Another common audiologic task involves giving the child two sentences, one louder than the other, at the same time. The audiologist is trying to identify the processing problem.
A speech-language pathologist can ﬁ nd out how well a person understands and uses language. A mental health professional can give you information about cognitive and behavioral challenges that may contribute to problems in some cases, or he or she may have suggestions that will be helpful. Because the audiologist can help with the functional problems of hearing and processing, and the speech-language pathologist is focused on language, they may work as a team with your child. All of these professionals seek to provide the best outcome for each child.
- What current research is being conducted?
In recent years, scientists have developed new ways to study the human brain through imaging. Imaging is a powerful tool that allows the monitoring of brain activity without any surgery. Imaging studies are already giving scientists new insights into auditory processing. Some of these studies are directed at understanding auditory processing disorders. One of the values of imaging is that it provides an objective, measurable view of a process. Many of the symptoms described as related to APD are described differently by different people.
Imaging will help identify the source of these symptoms. Other scientists are studying the central auditory nervous system. Cognitive neuroscientists are helping to describe how the processes that mediate sound recognition and comprehension work in both normal and disordered systems.
Research into the rehabilitation of child language disorders continues. It is important to know that much research is still needed to understand auditory processing problems, related disorders, and the best interventions for each child or adult. All the strategies undertaken will need to be suited to the needs of the individual child, and their effectiveness will need to be continuously evaluated. The standard for determining if a treatment is effective is that a patient can reasonably expect to beneﬁt from it.
- What treatments are available for auditory processing difficulty?
Much research is still needed to understand APD problems, related disorders, and the best intervention for each child or adult. Several strategies are available to help children with auditory processing difﬁculties. Some of these are commercially available, but have not been fully studied. Any strategy selected should be used under the guidance of a team of professionals, and the effectiveness of the strategy needs to be evaluated. Researchers are currently studying a variety of approaches to treatment. Several strategies you may hear about include:
- Auditory trainers are electronic devices that allow a person to focus attention on a speaker and reduce the interference of background noise. They are often used in classrooms, where the teacher wears a microphone to transmit sound and the child wears a headset to receive the sound (such as an FM system). Children who wear hearing aids can use them in addition to the auditory trainer.
- Environmental modiﬁcations such as classroom acoustics, placement, and seating may help. An audiologist may suggest ways to improve the listening environment, and he or she will be able to monitor any changes in hearing status.
- Exercises to improve language-building skills can increase the ability to learn new words and increase a child’s language base.
- Auditory memory enhancement, a procedure that reduces detailed information to a more basic representation, may help. Also, informal auditory training techniques can be used by teachers and therapists to address speciﬁc difﬁculties.
- Auditory integration training may be promoted by practitioners as a way to retrain the auditory system and decrease hearing distortion. However, current research has not proven the beneﬁts of this treatment.
- What is a vestibular schwannoma (acoustic neuroma)?
A vestibular schwannoma (also known as acoustic neuroma, acoustic neurinoma, or acoustic neurilemoma) is a benign, usually slow-growing tumor that develops from the balance and hearing nerves supplying the inner ear. The tumor comes from an overproduction of Schwann cells–the cells that normally wrap around nerve fibers like onion skin to help support and insulate nerves. As the vestibular schwannoma grows, it presses against the hearing and balance nerves, usually causing unilateral (one-sided) or asymmetric hearing loss, tinnitus (ringing in the ear), and dizziness/loss of balance. As the tumor grows, it can interfere with the face sensation nerve (the trigeminal nerve), causing facial numbness. Vestibular schwannomas can also press on the facial nerve (for the muscles of the face) causing facial weakness or paralysis on the side of the tumor. If the tumor becomes large, it will eventually press against nearby brain structures (such as the brainstem and the cerebellum), becoming life-threatening.
- How is a vestibular schwannoma diagnosed?
Unilateral/asymmetric hearing loss and/or tinnitus and loss of balance/dizziness are early signs of a vestibular schwannoma. Unfortunately, early detection of the tumor is sometimes difficult because the symptoms may be subtle and may not appear in the beginning stages of growth. Also, hearing loss, dizziness, and tinnitus are common symptoms of many middle and inner ear problems (the important point here is that unilateral or asymmetric symptoms are the worrisome ones). Once the symptoms appear, a thorough ear examination and hearing test (audiogram) are essential for proper diagnosis. Computerized tomography (CT) scans, enhanced with intravenous dye (contrast), and magnetic resonance imaging (MRI) are critical in the early detection of a vestibular schwannoma and are helpful in determining the location and size of a tumor and in planning its microsurgical removal.
- How is a vestibular schwannoma treated?
Early diagnosis of a vestibular schwannoma is key to preventing its serious consequences. There are three options for managing a vestibular schwannoma: (1) surgical removal; (2) radiation; and (3) monitoring. Typically, the tumor is surgically removed (excised). The exact type of operation done depends on the size of the tumor and the level of hearing in the affected ear. If the tumor is very small, hearing may be saved and accompanying symptoms may improve. As the tumor grows larger, surgical removal is more complicated because the tumor may have damaged the nerves that control facial movement, hearing, and balance and may also have affected other nerves and structures of the brain.
The removal of tumors affecting the hearing, balance, or facial nerves can make the patient’s symptoms worse because sections of these nerves may also need to be removed with the tumor.
As an alternative to conventional surgical techniques, radiosurgery (that is, radiation therapy—the “gamma knife” or LINAC) may be used to reduce the size or limit the growth of the tumor. Radiation therapy is sometimes the preferred option for elderly patients, patients in poor medical health, patients with bilateral vestibular schwannoma (tumor affecting both ears), or patients whose tumor is affecting their only hearing ear. In some cases, usually elderly or medically infirm patients, and small tumours it may be reasonable to “watch” the tumor for growth. Repeat MRI over time is used to carefully monitor the tumor for any growth.
- What is the difference between unilateral and bilateral vestibular schwannomas?
Unilateral vestibular schwannomas affect only one ear. They account for approximately 8 percent of all tumors inside the skull; one out of every 100,000 individuals per year develops a vestibular schwannoma. Symptoms may develop at any age but usually occur between the ages of 30 and 60 years. Unilateral vestibular schwannomas are not hereditary.
Bilateral vestibular schwannomas affect both hearing nerves and are usually associated with a genetic disorder called neurofibromatosis type 2 (NF 2). Half of affected individuals have inherited the disorder from an affected parent and half seem to have a mutation for the first time in their family. Each child of an affected parent has a 50 percent chance of inheriting the disorder. Unlike those with a unilateral vestibular schwannoma, individuals with NF2 usually develop symptoms in their teens or early adulthood. In addition, patients with NF2 usually develop multiple brain and spinal cord related tumors. They also can develop tumors of the nerves important for swallowing, speech, eye and facial movement, and facial sensation. Determining the best management of the vestibular schwannomas as well as the additional nerve, brain, and spinal cord tumors is more complicated than deciding how to treat a unilateral vestibular schwannoma. Further research is needed to determine the best treatment for individuals with NF2.
Scientists believe that both unilateral and bilateral vestibular schwannomas form following the loss of the function of a gene on chromosome 22. (A gene is a small section of DNA responsible for a particular characteristic like hair color or skin tone). Scientists believe that this particular gene on chromosome 22 produces a protein that controls the growth of Schwann cells. When this gene malfunctions, Schwann cell growth is uncontrolled, resulting in a tumor. Scientists also think that this gene may help control the growth of other types of tumors. In NF2 patients, the faulty gene on chromosome 22 is inherited. For individuals with unilateral vestibular schwannoma, however, some scientists hypothesize that this gene somehow loses its ability to function properly.
- What Research Is Being Done?
Scientists are working to better understand how the gene works so they can begin to develop gene therapy to control the overproduction of Schwann cells in individuals with vestibular schwannoma. Also, learning more about the way genes help control Schwann cell growth may help prevent other brain tumors.
- What is Ear Wax?
Ear wax can be a very exciting topic! Ear wax, also called cerumen, is a naturally occuring substance that is made up of secretions from special sweat glands called “ceruminous glands” and “sebaceous” or oil glands, as well as dead skin cells, and other debris. Contrary to popular belief, cerumen is actually quite functional; it serves as a lubricant, water repellent, an anti-bacterial/anti-fungal agent, and an entrapper of dust and even insects. Its function is similar to eyes producing tears. Imagine your eyes if you didn’t have tears.
Believe it or not – not all ear wax is created equal. Ear wax can be hard or soft; yellow or brown; flaky or runny. There are many types of ear wax and these are genetically conditioned. For example, people of Asian descent and Aboriginal peoples have a dry flaky wax that has been referred to as “oatbran” wax. A physician would find this type of wax relatively easy to remove. In contrast to the dry wax, Western Europeans and those of African descent generally have a softer, stickier type of wax.
- Why Do I Accumulate Wax?
Ear wax will naturally migrate outwards out of the ear canal. However, this skin migration does have some barriers, and will only work if the wax has not been pushed deeply in to the ear. The use of hearing aids can be one reason why wax is pushed deeply into the ear. Another is the use of earplugs – either for listening to music, or to prevent loud noise from factories. There are some people that have very narrow ear canals; with these people ear wax can become stuck in the ear and will block the ear. Of course, we cannot forget the use of Q-tips (which inevitably do more damage than good) that push the wax further down the ear canal!
- How Can I Keep My Ears Clean?
It is fine to remove any ear wax after a shower or bath from the outer part of the ear (the part that you see when you look at a person), but do NOT use Q-tips or any other object that probes the ear. Not only can you push the ear wax further in, but there is a risk of scratching the ear canal wall, or even damaging the eardrum.
Some people may be prone to building up ear wax, while others hardly get any at all. If you suspect an abnormal amount of wax, see your family doctor or ear doctor. They may recommend putting drops of olive oil or mineral oil in the ear canal a few days before it is removed. These types of oils will soften the wax, and make the removal process more enjoyable.
However, nothing should be put in the ear without a consultation with an appropriate health care individual. People with holes in their eardrums should be wary of putting any fl uids in their ears unless instructed to by a physician.
Itchiness in the ears can be a sign of either too much or too little wax. Generally physicians will only remove enough ear wax in order to get a good look at the eardrum. Most physicians will leave some wax in the ear in order to let it do its protective work.
- What is Ménière’s disease?
Ménière’s disease is a disorder of the inner ear that causes severe dizziness (vertigo), ringing in the ears (tinnitus), hearing loss, and a feeling of fullness or congestion in the ear. Ménière’s disease usually affects only one ear.
Attacks of dizziness may come on suddenly or after a short period of tinnitus or muffled hearing. Some people will have single attacks of dizziness separated by long periods of time. Others may experience many attacks closer together over a number of days. Some people with Ménière’s disease have vertigo so extreme that they lose their balance and fall. These episodes are called “drop attacks.” Ménière’s disease can develop at any age, but it is more likely to happen to adults between 40 and 60 years of age.
- What causes the symptoms of Ménière’s disease?
The symptoms of Ménière’s disease are caused by the buildup of fluid in the compartments of the inner ear, called the labyrinth. The labyrinth contains the organs of balance (the semicircular canals and otolithic organs) and of hearing (the cochlea). It has two sections: the bony labyrinth and the membranous labyrinth. The membranous labyrinth is filled with a fluid called endolymph that, in the balance organs, stimulates receptors as the body moves. The receptors then send signals to the brain about the body’s position and movement. In the cochlea, fluid is compressed in response to sound vibrations, which stimulates sensory cells that send signals to the brain.
In Ménière’s disease, the endolymph buildup in the labyrinth interferes with the normal balance and hearing signals between the inner ear and the brain. This abnormality causes vertigo and other symptoms of Ménière’s disease.
- Why do people get Ménière’s disease?
Many theories exist about what happens to cause Ménière’s disease, but no definite answers are available. Some researchers think that Ménière’s disease is the result of constrictions in blood vessels similar to those that cause migraine headaches. Others think Ménière’s disease could be a consequence of viral infections, allergies, or autoimmune reactions. Because Ménière’s disease appears to run in families, it could also be the result of genetic variations that cause abnormalities in the volume or regulation of endolymph fluid.
- How does a doctor diagnose Ménière’s disease?
Ménière’s disease is most often diagnosed and treated by an otolaryngologist (commonly called an ear, nose, and throat doctor, or ENT). However, there is no definitive test or single symptom that a doctor can use to make the diagnosis. Diagnosis is based upon your medical history and the presence of:
- Two or more episodes of vertigo lasting at least 20 minutes each
- Temporary hearing loss
- A feeling of fullness in the ear
Some doctors will perform a hearing test to establish the extent of hearing loss caused by Ménière’s disease. To rule out other diseases, a doctor also might request magnetic resonance imaging (MRI) or computed tomography (CT) scans of the brain.
- How is Ménière’s disease treated?
Ménière’s disease does not have a cure yet, but your doctor might recommend some of the treatments below to help you cope with the condition.
- Medications. The most disabling symptom of an attack of Ménière’s disease is dizziness. Prescription drugs such as meclizine, diazepam, glycopyrrolate, and lorazepam can help relieve dizziness and shorten the attack.
- Salt restriction and diuretics. Limiting dietary salt and taking diuretics (water pills) help some people control dizziness by reducing the amount of fluid the body retains, which may help lower fluid volume and pressure in the inner ear.
- Other dietary and behavioral changes. Some people claim that caffeine, chocolate, and alcohol make their symptoms worse and either avoid or limit them in their diet. Not smoking also may help lessen the symptoms.
- Cognitive therapy. Cognitive therapy is a type of talk therapy that helps people focus on how they interpret and react to life experiences. Some people find that cognitive therapy helps them cope better with the unexpected nature of attacks and reduces their anxiety about future attacks.
- Injections. Injecting the antibiotic gentamicin into the middle ear helps control vertigo but significantly raises the risk of hearing loss because gentamicin can damage the microscopic hair cells in the inner ear that help us hear. Some doctors inject a corticosteroid instead, which often helps reduce dizziness and has no risk of hearing loss.
- Pressure pulse treatment. The U.S. Food and Drug Administration (FDA) recently approved a device for Ménière’s disease that fits into the outer ear and delivers intermittent air pressure pulses to the middle ear. The air pressure pulses appear to act on endolymph fluid to prevent dizziness.
- Surgery. Surgery may be recommended when all other treatments have failed to relieve dizziness. Some surgical procedures are performed on the endolymphatic sac to decompress it. Another possible surgery is to cut the vestibular nerve, although this occurs less frequently.
- Alternative medicine. Although scientists have studied the use of some alternative medical therapies in Ménière’s disease treatment, there is still no evidence to show the effectiveness of such therapies as acupuncture or acupressure, tai chi, or herbal supplements such as gingko biloba, niacin, or ginger root. Be sure to tell your doctor if you are using alternative therapies, since they sometimes can impact the effectiveness or safety of conventional medicines.
- What is the outlook for someone with Ménière’s disease?
Scientists estimate that six out of 10 people either get better on their own or can control their vertigo with diet, drugs, or devices. However, a small group of people with Ménière’s disease will get relief only by undergoing surgery.
- What can be done?
Insights into the biological mechanisms in the inner ear that cause Ménière’s disease will guide scientists as they develop preventive strategies and more effective treatment. Research is currently being done on:
- Determining the most effective dose of gentamicin with the least amount of risk for hearing loss.
- Developing an in-ear device that uses a programmable microfluid pump (the size of a computer chip) to precisely deliver vertigo-relieving drugs to the inner ear.
- Studying the relationship between endolymph volume and inner ear function to determine how much endolymph is “too much.” Researchers are hoping to develop methods for manipulating inner ear fluids and treatments that could lower endolymph volume and reduce or eliminate dizziness.
- What is otosclerosis?
Otosclerosis is the abnormal growth of bone of the middle ear. This bone prevents structures within the ear from working properly and causes hearing loss. For some people with otosclerosis, the hearing loss may become severe.
- How does otosclerosis cause hearing impairment?
Otosclerosis can cause different types of hearing loss, depending on which structure within the ear is affected. Otosclerosis usually affects the last bone in the chain, the stapes, which rests in the entrance to the inner ear (the oval window). The abnormal bone fixates the stapes in the oval window and interferes with sound passing waves to the inner ear.
Otosclerosis usually causes a conductive hearing loss, a hearing loss caused by a problem in the outer or middle ear. Less frequently, otosclerosis may cause a sensorineural hearing loss (damaged sensory cells and/or nerve fibers of the inner ear), as well as a conductive hearing loss.
- What causes otosclerosis?
The cause of otosclerosis is not fully understood, although research has shown that otosclerosis tends to run in families and may be hereditary, or passed down from parent to child. People who have a family history of otosclerosis are more likely to develop the disorder. On average, a person who has one parent with otosclerosis has a 25 percent chance of developing the disorder. If both parents have otosclerosis, the risk goes up to 50 percent. Research shows that white, middle-aged women are most at risk. Some research suggests a relationship between otosclerosis and the hormonal changes associated with pregnancy. While the exact cause remains unknown, there is some evidence associating viral infections (such as measles) and otosclerosis.
- What are the symptoms of otosclerosis?
Hearing loss is the most frequent symptom of otosclerosis. The loss may appear very gradually. Many people with otosclerosis first notice that they cannot hear low-pitched sounds or that they can no longer hear a whisper.
In addition to hearing loss, some people with otosclerosis may experience dizziness, balance problems, or tinnitus. Tinnitus is a sensation of ringing, roaring, buzzing, or hissing in the ears or head that accompanies many forms of hearing loss.
- How is otosclerosis diagnosed?
An examination by an otolaryngologist (ear, nose, and throat physician) or otologist (ear physician) is needed to rule out other diseases or health problems that may cause these same symptoms. An audiologist is a hearing health care professional who is trained to identify, measure, and rehabilitate hearing impairment and related disorders. An audiologist uses a variety of tests and procedures to assess hearing and balance function. The audiologist may produce an audiogram (a graph that shows a person’s hearing sensitivity) and a tympanogram (a graph that shows how well the middle ear functions to conduct sound). Discuss these results with your audiologist/otologist.
- What can be done?
In many cases surgery is an option for treatment of otosclerosis. In an operation called a stapedectomy, a surgeon (otolaryngologist or otologist) bypasses the diseased bone with a prosthetic device that allows sound waves to be passed to the inner ear. It is important to discuss the risks and possible complications of this procedure, as well as the benefits, with the surgeon. In rare cases, surgery can worsen the hearing loss.
If the hearing loss is mild, surgery may not be an option. Also, on occasion, some hearing loss persists after surgery. A properly fitted hearing aid may help some people with otosclerosis in situations that include persistent hearing loss. A hearing aid is designed to compensate for a hearing loss by amplifying sound. An audiologist can discuss the various types of hearing aids available and make a recommendation based on the specific needs of an individual.
- What research is being done on otosclerosis?
Scientists are conducting research to improve understanding of otosclerosis. Genetic studies continue in order to identify the gene or genes that may lead to this disorder. Other researchers are studying the effectiveness of lasers currently used in surgery, of amplification devices, and of various stapes prostheses. Improved diagnostic techniques are also being examined and developed.
- 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. 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.
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 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 when conventional hearing aids only provide little benefit.
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?
The National Institute on Deafness and Other Communication Disorders (NIDCD) in the United States 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.
- What Is Sudden Deafness?
Sudden Sensorineural Hearing Loss (SSHL), or sudden deafness, is a rapid loss of hearing. SSHL can happen to a person all at once or over a period of up to 3 days. It should be considered a medical emergency. A person who experiences SSHL should visit a doctor immediately.
A doctor can determine whether a person has experienced SSHL by conducting a normal hearing test. If a loss of at least 30 decibels in three connected frequencies is discovered, it is diagnosed as SSHL. A decibel is a measure of sound. A decibel level of 30 is half as loud as a normal conversation. A frequency is another way of measuring sound. Frequencies measure sound waves and help to determine what makes one sound different from another sound.
Hearing loss affects only one ear in 9 out of 10 people who experience SSHL. Many people notice it when they wake up in the morning. Others first notice it when they try to use the deafened ear, such as when they make a phone call. Still others notice a loud, alarming “pop” just before their hearing disappears. People with SSHL often experience dizziness or a ringing in their ears (tinnitus), or both.
Some patients recover completely without medical intervention, often within the first 3 days. This is called a spontaneous recovery. Others get better slowly over a 1 or 2 week period. Although a good to excellent recovery is likely, 15 percent of those with SSHL experience a hearing loss that gets worse over time.
- What Causes Sudden Deafness?
Though there are more than 100 possible causes of sudden deafness, it is rare for a specific cause to be precisely identified. Only 10 to 15 percent of patients with SSHL know what caused their loss. Normally, diagnosis is based on the patient’s medical history. Possible causes include the following:
- Infectious diseases.
- Trauma, such as a head injury.
- Abnormal tissue growth.
- Immunologic diseases such as Cogan’s syndrome.
- Toxic causes, such as snake bites.
- Circulatory problems.
- Ototoxic drugs (drugs that harm the ear).
- Neurologic causes such as multiple sclerosis.
- Relation to disorders such as Ménière’s disease.
- What Are the Treatments for Sudden Deafness?
People who experience SSHL should see a physician immediately. Doctors believe that finding medical help fast increases the chances for recovery. Several treatments are used for SSHL, but researchers are not yet certain which is the best for any one cause. If a specific cause is identified, a doctor may prescribe antibiotics for the patient. Or, a doctor may advise a patient to stop taking any medicine that can irritate or damage the ear.
The most common therapy for SSHL, especially in cases with an unknown cause, is treatment with steroids. Steroids are used to treat many different disorders and usually work to reduce inflammation, decrease swelling, and help the body fight illness. Steroid treatment helps some SSHL patients who also have conditions that affect the immune system, which is the body’s defense against disease.
Another common method that may help some patients is a diet low in salt. Researchers believe that this method aids people with SSHL who also have Ménière’s disease, a hearing and balance disorder.
- What is Usher syndrome?
Usher syndrome is the most common condition that affects both hearing and vision. A syndrome is a disease or disorder that has more than one feature or symptom. The major symptoms of Usher syndrome are hearing loss and an eye disorder called retinitis pigmentosa, or RP. RP causes night-blindness and a loss of peripheral vision (side vision) through the progressive degeneration of the retina. The retina is a light-sensitive tissue at the back of the eye and is crucial for vision. As RP progresses, the field of vision narrows—a condition known as “tunnel vision”—until only central vision (the ability to see straight ahead) remains. Many people with Usher syndrome also have severe balance problems. There are three clinical types of Usher syndrome: type 1, type 2, and type 3.
- What are the Chances of Inheriting a Recessive Disorder?
Genetic disorders can be caused by a change(s) in a gene. Every individual has two copies of the same gene. Genetic disorders are inherited in different ways. Usher syndrome is a recessive disorder.
- a person must inherit a change in the same gene from each parent ~ in order to have the disorder
- a person with one changed gene does not have the disorder, but can pass either the changed or the unchanged gene on to his or her child
An individual with Usher syndrome usually has inherited a change in the same gene from each parent
An individual who has one changed Usher syndrome gene is called a carrier. When two carriers of the same Usher syndrome gene have a child together, with each birth there is a:
- 1-in-4 chance of having a child with Usher syndrome
- 2-in-4 chance of having a child who is a carrier
- 1-in-4 chance of having a child who neither has Usher syndrome nor is a carrier
- Who is affected by Usher syndrome?
Approximately 3 to 6 percent of all children who are deaf and another 3 to 6 percent of children who are hard-of-hearing have Usher syndrome. In developed countries such as Canada, about four babies in every 100,000 births have Usher syndrome.
- What causes Usher syndrome?
Usher syndrome is inherited, which means that it is passed from parents to their children through genes. Genes are located in almost every cell of the body. Genes contain instructions that tell cells what to do. Every person inherits two copies of each gene, one from each parent. Sometimes genes are altered, or mutated. Mutated genes may cause cells to act differently than expected.
Usher syndrome is inherited as an autosomal recessive trait. The term autosomal means that the mutated gene is not located on either of the chromosomes that determine a person’s sex; in other words, both males and females can have the disorder and can pass it along to a child. The word recessive means that, to have Usher syndrome, a person must receive a mutated form of the Usher syndrome gene from each parent. If a child has a mutation in one Usher syndrome gene but the other gene is normal, he or she is predicted to have normal vision and hearing. People with a mutation in a gene that can cause an autosomal recessive disorder are called carriers, because they “carry” the gene with a mutation, but show no symptoms of the disorder. If both parents are carriers of a mutated gene for Usher syndrome, they will have a one-in-four chance of having a child with Usher syndrome with each birth.
Usually, parents who have normal hearing and vision do not know if they are carriers of an Usher syndrome gene mutation. Currently, it is not possible to determine whether a person who does not have a family history of Usher syndrome is a carrier. Scientists at the National Institute on Deafness and Other Communication Disorders (NIDCD) in the United States are hoping to change this, however, as they learn more about the genes responsible for Usher syndrome.
- What are the characteristics of the three types of Usher syndrome?
Children with type 1 Usher syndrome are profoundly deaf at birth and have severe balance problems. Many of these children obtain little or no benefit from hearing aids. Parents should consult their doctor and other hearing health professionals as early as possible to determine the best communication method for their child. Intervention should be introduced early, during the first few years of life, so that the child can take advantage of the unique window of time during which the brain is most receptive to learning language, whether spoken or signed. If a child is diagnosed with type 1 Usher syndrome early on, before he or she loses the ability to see, that child is more likely to benefit from the full spectrum of intervention strategies that can help him or her participate more fully in life’s activities.
Because of the balance problems associated with type 1 Usher syndrome, children with this disorder are slow to sit without support and typically don’t walk independently before they are 18 months old. These children usually begin to develop vision problems in early childhood, almost always by the time they reach age 10. Vision problems most often begin with difficulty seeing at night, but tend to progress rapidly until the person is completely blind.
Children with type 2 Usher syndrome are born with moderate to severe hearing loss and normal balance. Although the severity of hearing loss varies, most of these children can benefit from hearing aids and can communicate orally. The vision problems in type 2 Usher syndrome tend to progress more slowly than those in type 1, with the onset of RP often not apparent until the teens.
Children with type 3 Usher syndrome have normal hearing at birth. Although most children with the disorder have normal to near-normal balance, some may develop balance problems later on. Hearing and sight worsen over time, but the rate at which they decline can vary from person to person, even within the same family. A person with type 3 Usher syndrome may develop hearing loss by the teens, and he or she will usually require hearing aids by mid- to late adulthood. Night blindness usually begins sometime during puberty. Blind spots appear by the late teens to early adulthood, and, by mid-adulthood, the person is usually legally blind.
- How is Usher syndrome diagnosed?
Because Usher syndrome affects hearing, balance, and vision, diagnosis of the disorder usually includes the evaluation of all three senses. Evaluation of the eyes may include a visual field test to measure a person’s peripheral vision, an electroretinogram (ERG) to measure the electrical response of the eye’s light-sensitive cells, and a retinal examination to observe the retina and other structures in the back of the eye. A hearing (audiologic) evaluation measures how loud sounds at a range of frequencies need to be before a person can hear them.
Vestibular function tests such as a videonystagmography (VNG) measures involuntary eye movements that help identify a balance problem.
Early diagnosis of Usher syndrome is very important. The earlier that parents know if their child has Usher syndrome, the sooner that child can begin special educational training programs to manage the loss of hearing and vision.
- Is genetic testing for Usher syndrome available?
So far, 11 genetic loci (a segment of chromosome on which a certain gene is located) have been found to cause Usher syndrome, and nine genes have been pinpointed that cause the disorder. They are:
- Type 1 Usher syndrome: MY07A, USH1C, CDH23, PCDH15, SANS
- Type 2 Usher syndrome: USH2A, VLGR1, WHRN
- Type 3 Usher syndrome: USH3A
With so many possible genes involved in Usher syndrome, genetic tests for the disorder are not conducted on a widespread basis. Diagnosis of Usher syndrome is usually performed through hearing, balance, and vision tests. Genetic testing for a few of the identified genes is clinically available. To learn about laboratories that conduct clinical testing, visit the Web site www.GeneTests.org and search the laboratory directory by typing in the term “Usher syndrome.” Genetic testing for additional Usher syndrome genes may be available through clinical research studies.
- How is Usher syndrome treated?
Currently, there is no cure for Usher syndrome. The best treatment involves early identification so that educational programs can begin as soon as possible. The exact nature of these programs will depend on the severity of the hearing and vision loss as well as the age and abilities of the person. Typically, treatment will include hearing aids, assistive listening devices, cochlear implants, or other communication methods such as American Sign Language; orientation and mobility training; and communication services and independent-living training that may include Braille instruction, low-vision services, or auditory training.
Some ophthalmologists believe that a high dose of vitamin A palmitate may slow, but not halt, the progression of retinitis pigmentosa. This belief stems from the results of a long-term clinical trial supported by the National Eye Institute and the Foundation for Fighting Blindness. Based on these findings, the researchers recommend that most adult patients with the common forms of RP take a daily supplement of 15,000 IU (international units) of vitamin A in the palmitate form under the supervision of their eye care professional. (Because people with type 1 Usher syndrome did not take part in the study, high-dose vitamin A is not recommended for these patients.) People who are considering taking vitamin A should discuss this treatment option with their health care provider before proceeding. Other guidelines regarding this treatment option include:
- Do not substitute vitamin A palmitate with a beta-carotene supplement.
- Do not take vitamin A supplements greater than the recommended dose of 15,000 IU or modify your diet to select foods with high levels of vitamin A.
- Women who are considering pregnancy should stop taking the high-dose supplement of vitamin A three months before trying to conceive due to the increased risk of birth defects.
- Women who are pregnant should stop taking the high-dose supplement of vitamin A due to the increased risk of birth defects.
In addition, according to the same study, people with RP should avoid using supplements of more than 400 IU of vitamin E per day.
- What research is being conducted on Usher syndrome?
Researchers are currently trying to identify all of the genes that cause Usher syndrome and determine the function of those genes. This research will lead to improved genetic counseling and early diagnosis, and may eventually expand treatment options. Scientists also are developing mouse models that have the same characteristics as the human types of Usher syndrome. Mouse models will make it easier to determine the function of the genes involved in Usher syndrome. Other areas of study include the early identification of children with Usher syndrome, treatment strategies such as the use of cochlear implants for hearing loss, and intervention strategies to help slow or stop the progression of RP.
- What are some of the latest research findings?
NIDCD researchers, along with collaborators from universities in New York and Israel, pinpointed a mutation, named R245X, of the PCDH15 gene that accounts for a large percentage of type 1 Usher syndrome in today’s Ashkenazi Jewish population. (The term “Ashkenazi” describes Jewish people who originate from Eastern Europe.) Based on this finding, the researchers conclude that Ashkenazi Jewish infants with bilateral, profound hearing loss who lack another known mutation that causes hearing loss should be screened for the R245X mutation.
- What is Waardenburg syndrome?
Waardenburg syndrome (WS) is an inherited disorder often characterized by varying degrees of hearing loss and changes in skin and hair pigmentation. The syndrome got its name from a Dutch eye doctor named Petrus Johannes Waardenburg who first noticed that people with differently colored eyes often had a hearing impairment. He went on to study over a thousand individuals in deaf families and found that some of them had certain physical characteristics in common.
One commonly observed characteristic of Waardenburg syndrome is two differently colored eyes. One eye is usually brown and the other blue. Sometimes, one eye has two different colors. Other individuals with Waardenburg syndrome may have unusually brilliant blue eyes.
People with WS may also have distinctive hair coloring, such as a patch of white hair or premature gray hair as early as age 12. Other possible physical features include a wide space between the inner corners of eyes called a broad nasal root. In addition persons with WS may have low frontal hairline and their eyebrows may connect. The levels of hearing loss associated with the syndrome can vary from moderate to profound.
Individuals with Waardenburg syndrome may have some or all of the traits of the syndrome. For example, a person with WS may have a white forelock, a patch of white hair near the forehead, and no hearing impairment. Others may have white patches of skin and severe hearing impairment. The severity of the hearing impairment varies among individuals with WS as do changes in the skin and hair, Some patients also have dizziness.
On rare occasions, WS has been associated with other conditions that are present at birth, such as intestinal disorders, elevation of the shoulder blade, and disorders of the spine. A facial abnormality, known as cleft lip and/or palate, also has been associated with WS.
- What are the types of Waardenburg syndrome?
There are at least four types of Waardenburg syndrome. The most common types of WS identified by scientists are Type 1 and Type 2. The different types of physical characteristics a person has determines the type of WS. Persons who have an unusually wide space between the inner corners of their eyes have WS Type 1. Hearing impairments occur in about 20 percent of individuals with this type of Waardenburg syndrome. Persons who do not have a wide space between the inner corners of their eyes, but who have many other WS characteristics are described as having WS Type 2. About 50 percent of persons with WS Type 2 have a hearing impairment or are Deaf or Hard of Hearing.
- What causes Waardenburg syndrome?
As a genetic disorder, Waardenburg syndrome is passed down from parent to child much like hair color, blood type, or other physical traits. A child receives genetic material from each parent. Because Waardenburg syndrome is a dominant condition, a child usually inherits the syndrome from just one parent who has the malfunctioning WS gene. Actually, there is a 50/50 chance that a child of an individual with WS will also have the syndrome.
- What research is being done?
Scientists have identified and located four different genes for Waardenburg syndrome: PAX3, MITF, EDNRB, and EDN3. WS type 1 and 3 have been associated with mutations in the PAX3 gene; WS type 2 with the MITF gene; and WS type 4 with the EDNRB and EDN3 genes. While scientists are studying all of these genes, currently, the most information is available on the PAX3 and MITF genes and their role in Waardenburg syndrome.
The PAX3 gene is located on chromosome 2 and controls some aspects of the development of the face and inner ear. The MITF gene is found on chromosome 3. It also controls the development of the ear and hearing. Scientists are now studying these genes to better understand how they operate in controlling the normal growth of the ear and the development of hearing. This information will help scientists understand why persons with WS sometimes develop hearing problems.