Nearly 30 million Americans have impaired hearing. The most
common cause of hearing loss in children is otitis media. For
the elderly-the largest group affected-excessive noise, drugs,
toxins, and heredity are the most frequent contributing factors.
Hearing loss is a medical disorder. In a limited
number of patients, it can be surgically corrected; medical
devices and rehabilitation can substantially reduce hearing
loss in the vast majority of patients who cannot be helped by
surgery. The medical specialists who diagnose and treat hearing
disorders are called otolaryngologists-head
and neck surgeons, or more commonly, "ear, nose and
Does not startle, move, cry or react in any way to unexpected
Does not awaken
to loud noises,
Does not turn
his/her head in the direction of your voice, or
Does not freely
He or she may
have some degree of hearing loss.
More than three million American children have
a hearing loss. An estimated 1.3 million of these children are
under three years of age. Parents and grandparents are usually
the first to discover hearing loss in a baby, because they spend
the most time with them. If at any time you suspect your baby
has a hearing loss, discuss it with your doctor. He or she may
recommend evaluation by an otolaryngologist-head and neck surgeon
(ear, nose and throat specialist).
Hearing loss can be temporary, caused by earwax
or middle ear infections. Many children with temporary hearing
loss can have their hearing restored through medical treatment
or minor surgery.
However, some children have sensorineural hearing
loss (sometimes called nerve deafness), which is permanent.
Most of these children have some usable hearing, and children
as young as three months of age can be fitted with hearing aids.
Early diagnosis, early fitting of hearing or other prosthetic
aids, and an early start on special education programs can help
maximize a child's existing hearing. This means your child will
get a head start on speech and language development.
So Your Child has a Hearing Loss: Next Steps for Parents is
a booklet published by the Alexander Graham Bell Association
for the Deaf and Hard of Hearing (AGBell). The AAO-HNS is posting
this online version of the booklet as a service to our members'
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One in 10 Americans has a hearing loss that affects his or her
ability to understand normal speech.Excessive noise
exposure is the most common cause of hearing loss.
Can Noise Really Hurt My Ears?
Yes, noise can be dangerous. If it is loud enough and lasts
long enough, it can damage your hearing.
The damage caused by noise, called sensorineural
hearing loss or nerve deafness, can be caused by several factors
other than noise, but noise-induced hearing loss is different
in one important way--it can be reduced or prevented altogether.
Can I "Toughen Up" My Ears?
No. If you think you have grown used to a loud noise, it probably
has damaged your ears, and there is no treatment--no medicine,
no surgery, not even a hearing aid--that completely restores
your hearing once it is damaged by noise.
How Does the Ear Work?
The ear has three main parts: the outer, middle,
and inner ear. The outer ear (the part you can see) opens into
the ear canal. The eardrum separates the ear canal from the
middle ear. Small bones in the middle ear help transfer sound
to the inner ear. The inner ear contains the auditory (hearing)
nerve, which leads to the brain.
Any source of sound sends vibrations or sound
waves into the air. These funnel through the ear opening, down
the ear canal, and strike your eardrum, causing it to vibrate.
The vibrations are passed to the small bones of the middle ear,
which transmit them to the hearing nerve in the inner ear. Here,
the vibrations become nerve impulses and go directly to the
brain, which interprets the impulses as sound: music, a slamming
door, a voice, etc.
When noise is too loud, it begins to kill the
nerve endings in the inner ear. As the exposure time to loud
noise increases, more and more nerve endings are destroyed.
As the number of nerve endings decreases, so does your hearing.
There is no way to restore life
to dead nerve endings; the damage is permanent.
How Can I Tell If a Noise Is Dangerous?
People differ in their sensitivity to noise. As a general rule,
noise may damage your hearing if you have to shout over background
noise to make yourself heard, the noise hurts your ears, it
makes your ears ring, or you have difficulty hearing for several
hours after exposure to the noise.
Sound can be measured scientifically in two
ways. Intensity, or loudness of sound, is measured in decibels.
Pitch is measured in frequency of sound vibrations per second.
A low pitch, such as a deep voice or a tuba, makes fewer vibrations
per second than a high voice or violin.
What Does Frequency of Sound Vibration
Have to Do with Hearing Loss?
Frequency is measured in cycles per second, or Hertz (Hz). The
higher the pitch of the sound, the higher the frequency.
Young children, who generally have the best
hearing, can often distinguish sounds from about 20 Hz, such
as the lowest note on a large pipe organ, to 20,000 Hz, such
as the high shrill of a dog whistle that many people are unable
Human speech, which ranges from 300 to 4,000
Hz, sounds louder to most people than noises at very high or
very low frequencies. When hearing impairment begins, the high
frequencies are usually lost first, which is why people with
hearing loss often have difficulty hearing the high pitched
voices of women and children. Loss of high frequency hearing
also can distort sound, so that speech is difficult to understand
even though it can be heard. People with hearing loss often
have difficulty detecting differences between certain words
that sound alike, especially words that contain S, F, SH, CH,
H, or soft C sounds, because the sound of these consonants is
in a much higher frequency range than vowels and other consonants.
What about Decibels?
Intensity of sound is measured in decibels (dB). The scale runs
from the faintest sound the human ear can detect, which is labeled
0 dB, to over 180 dB, the noise at a rocket pad during launch.
Decibels are measured logarithmically. This
means that as decibel intensity increases by units of 10, each
increase is 10 times the lower figure. Thus, 20 decibels is
10 times the intensity of 10 decibels, and 30 decibels is 100
times as intense as 10 decibels.
Faintest sound heard by human ear.
Whisper, quiet library.
Normal conversation, sewing machine, typewriter.
Lawnmower, shop tools, truck traffic; 8
hours per day is the maximum exposure to protect 90% of
Chainsaw, pneumatic drill, snowmobile;
2 hours per day is the maximum exposure without protection.
Sandblasting, loud rock concert, auto horn;
15 minutes per day is the maximum exposure without protection.
Gun muzzle blast, jet engine; noise causes
pain and even brief exposure injures unprotected ears. Maximum
allowed noise with hearing protectors.
How High Can the Decibels Go without
Affecting My Hearing?
Many experts agree that continual exposure to
more than 85 decibels is dangerous.
Does the Length of Time I Hear a Noise
Have Anything to Do with the Danger to My Hearing?
It certainly does. The longer you are exposed to a loud noise,
the more damaging it may be. Also, the closer you are to the
source of intense noise, the more damaging it is.
Every gunshot produces a noise that could damage
the ears of anyone in close hearing range. Large bore guns and
artillery is the worse because they are the loudest. But even
cap guns and firecrackers can damage your hearing if the explosion
is close to your ear. Anyone who uses firearms without some
form of ear protection risks hearing loss.
Recent studies show an alarming increase in
hearing loss in youngsters. Evidence suggests that loud rock
music along with increased use of portable radios with earphones
may be responsible for this phenomenon.
Can Noise Affect More Than My Hearing?
A ringing in the ears, called tinnitus,
commonly occurs after noise exposure, and it often becomes permanent.
Some people react to loud noise with anxiety and irritability,
an increase in pulse rate and blood pressure, or an increase
in stomach acid. Very loud noise can reduce efficiency in performing
difficult tasks by diverting attention from the job.
Who Should Wear Hearing Projectors?
If you must work in an excessively noisy environment, you should
wear protectors. You should also wear them when using power
tools, noisy yard equipment, or firearms, or riding a motorcycle
What Are the Laws for on-the-Job Exposure?
to noise above 85 dB will cause a gradual hearing loss in a
significant number of individuals, and louder noises will accelerate
ears, the allowed exposure time decreases by one-half for each
5 dB increase in the average noise level. For instance, exposure
is limited to 8 hours at 90 dB, 4 hours at 95 dB, and
2 hours at 100 dB.
permissible noise exposure for the unprotected ear is 115 dB
for 15 minutes/day. Any noise above 140 dB is not permitted.
The Occupational Safety and Health Administration, in its Hearing
Conservation Amendment of 1983, requires hearing conservation
programs in noisy work places. This includes a yearly hearing
test for the approximately five million workers exposed to an
average of 85 dB or more of noise during an 8-hour work day.
Ideally, noisy machinery and work places should
be engineered to be more quiet or the worker's time in the noise
should be reduced; however, the cost of these actions is often
prohibitive. As an alternative, individual hearing protectors
are required when noise averages more than 90 dB during an 8-hour
When noise measurements indicate that hearing
protectors are needed, the employer must offer at least one
type of earplug and one type of earmuff without cost to employees.
If the yearly hearing tests reveal hearing loss of 10 dB or
more in higher pitches in either ear, the worker must be informed
and must wear hearing protectors when noise averages more than
85 dB for an 8-hour day.
Larger losses of hearing and/or the possibility
of ear disease should result in referral to an ear, nose and
throat physician (otolaryngologist).
What Are Hearing Protectors? How Effective
Hearing protection devices decrease the intensity of sound that
reaches the eardrum. They come in two forms: earplugs and earmuffs.
Earplugs are small inserts that fit into the
outer ear canal. They must be snugly sealed so the entire circumference
of the ear canal is blocked. An improperly fitted, dirty or
worn-out plug may not seal and can irritate the ear canal. They
are available in a variety of shapes and sizes to fit individual
ear canals and can be custom made. For people who have trouble
keeping them in their ears, they can be fitted to a headband.
Earmuffs fit over the entire outer ear to form
an air seal so the entire circumference of the ear canal is
blocked, and they are held in place by an adjustable band. Earmuffs
will not seal around eyeglasses or long hair, and the adjustable
headband tension must be sufficient to hold earmuffs firmly
around the ear.
Properly fitted earplugs or muffs reduce noise
15 to 30 dB. The better earplugs and muffs are approximately
equal in sound reductions, although earplugs are better for
low frequency noise and earmuffs for high frequency noise.
Simultaneous use of earplugs and muffs usually
adds 10 to 15dB more protection than either used alone. Combined
use should be considered when noise exceeds 105 dB.
Why Can't I just Stuff My Ears with
Ordinary cotton balls or tissue paper wads stuffed into the
ear canals are very poor protectors; they reduce noise only
by approximately 7 dB.
What Are the Common Problems of Hearing
Studies have shown that one-half of the workers wearing hearing
protectors receive one-half or less of the noise reduction potential
of their protectors because these devices are not worn
continuously while in noise or because they do not fit properly.
A hearing protector that gives an average of
30 dB of noise reduction if worn continuously during an 8-hour
work day becomes equivalent to only 9 dB of protection if taken
off for one hour in the noise. This is because decibels are
measured on a logarithmic scale, and there is a 10-fold increase
in noise energy for each 10 dB increase.
During the hour with unprotected ears, the worker
is exposed to 1,000 times more sound energy than if earplugs
or muffs had been worn.
In addition, noise exposure is cumulative. So
the noise at home or at play must be counted in the total exposure
during any one day. A maximum allowable while on-the-job followed
by exposure to a noisy lawnmower or loud music will definitely
exceed the safe daily limit.
Even if earplugs and/or muffs are worn continuously
while in noise, they do little good if there is an incomplete
air seal between the hearing protector and the skin.
When using hearing protectors, you will hear
your own voice as louder and deeper. This is a useful sign that
the hearing protectors are properly positioned.
Can I Hear Other People and Machine
Problems If I Wear Hearing Protectors?
Just as sunglasses help vision in very bright light, so do hearing
protectors enhance speech understanding in very noisy places.
Even in a quiet setting, a normal-hearing person wearing hearing
protectors should be able to understand a regular conversation.
Hearing protectors do slightly reduce the ability
of those with damaged hearing or poor comprehension of language
to understand normal conversation. However, it is essential
that persons with impaired hearing wear earplugs or muffs to
prevent further inner ear damage.
It has been argued that hearing protectors might
REDUCE a worker's ability to hear the noises that signify an
improperly functioning machine. However, most workers readily
adjust to the quieter sounds and can still detect such problems.
What If My Hearing Is Already Damaged?
How Can I Tell?
Hearing loss usually develops over a period of several years.
Since it is painless and gradual, you might not notice it. What
you might notice is a ringing or other sound in your ear (called
tinnitus), which could
be the result of long-term exposure to noise that has damaged
the hearing nerve. Or, you may have trouble understanding what
people say; they may seem to be mumbling, especially when you
are in a noisy place such as in a crowd or at a party. This
could be the beginning of high-frequency hearing loss; a hearing
test will detect it.
If you have any of these symptoms, you may have
nothing more serious than impacted wax or an ear infection,
which might be simply corrected. However, it might be hearing
loss from noise. In any case, take no chances with noise-the
hearing loss it causes is permanent. If you suspect
a hearing loss, call for an appointment today 972-492-6990.
I sometimes hear ringing in my ears.
Is this unusual?
Not at all. Tinnitus is the name for these head
noises, and they are very
common. Nearly 36 million Americans suffer from this discomfort.
Tinnitus may come and go, or you may be aware of a continuous
sound. It can vary in pitch from a low roar to a high squeal
or whine, and you may hear it in one or both ears. When the
ringing is constant, it can be annoying and distracting. More
than seven million people are afflicted so severely that they
cannot lead normal lives.
Can other people hear the noise in my
Not usually, but sometimes they are able to
hear a certain type of tinnitus. This is called "objective
tinnitus," and it caused either by abnormalities in blood
vessels around the outside of the ear or by muscle spasms, which
may sound like clicks or crackling inside the middle ear.
What causes tinnitus?
Most tinnitus comes from damage to the microscopic
endings of the hearing nerve in the inner ear. The health of
these nerve endings is important for acute hearing, and injury
to them brings on hearing loss and often tinnitus. If you are
older, advancing age is generally accompanied by a certain amount
of hearing nerve impairment and tinnitus. If you are younger,
exposure to loud noise is probably the leading cause of tinnitus,
and often damages hearing as well.
There are many causes for "subjective tinnitus,"
the noise only you can hear. Some causes are not serious (a
small plug of wax in the ear canal might cause temporary tinnitus).
Tinnitus can also be a symptom of stiffening of the middle ear
Tinnitus may also be caused by allergy,
high or low blood pressure (blood circulation problems), a tumor,
diabetes, thyroid problems, injury to the head or neck, and
a variety of other causes including medications such as anti-inflammatories,
antibiotics, sedatives, antidepressants, and aspirin. If you
take aspirin and your ears ring, talk to your doctor about dosage
in relation to your size.
Treatment will be quite different in each case of tinnitus.
It is important to see an otolaryngologist to investigate the
cause of your tinnitus so that the best treatment can be determined.
What is the treatment?
In most cases, there is no specific treatment
for ear and head noise. If your otolaryngologist finds a specific
cause of your tinnitus, he or she may be able to eliminate the
noise. But, this determination may require extensive testing
including X-rays, balance tests, and laboratory work. However,
most causes cannot be identified. Occasionally, medicine may
help the noise. The medications used are varied, and several
may be tried to see if they help.
The following list of DOs and DON'Ts
can help lessen the severity of tinnitus:
Avoid exposure to loud sounds and noises.
Get your blood
pressure checked. If it is high, get your doctor's help to control
intake of salt. Salt impairs blood circulation.
such as coffee, tea, cola, and tobacco.
to improve your circulation.
rest and avoid fatigue.
about the noise. Recognize your head noise as an annoyance and
learn to ignore it as much as possible.
What can help me cope with tinnitus?
Concentration and relaxation exercises can help
to control muscle groups and circulation throughout the body.
The increased relaxation and circulation achieved by these exercises
can reduce the intensity of tinnitus in some patients.
Masking. Tinnitus is usually
more bothersome in quiet surroundings. A competing sound at
a constant low level, such as a ticking clock or radio static
(white noise), may mask the tinnitus and make it less noticeable.
Products that generate white noise are also available through
catalogs and specialty stores.
Hearing Aids. If you have a
hearing loss, a hearing aid(s) may reduce head noise while wearing
it and sometimes cause it to go away temporarily. It is important
not to set the hearing aid at excessively loud levels, as this
can worsen the tinnitus in some cases. However, a thorough trial
before purchase of a hearing aid is advisable if your primary
purpose is the relief of tinnitus.
Tinnitus maskers can be combined within
hearing aids. They emit a competitive but pleasant
sound that can distract you from head noise. Some people find
that a tinnitus masker may even suppress the head noise for
several hours after it is used, but this is not true for all
Prior to any treatment of tinnitus or head noise,
it is important that you have a thorough examination and evaluation
by your otolaryngologist. An essential part of your treatment
will be your understanding of tinnitus and its causes.
I don't hear well. What should I do?
What should I expect?
Because some hearing problems can be medically
corrected, first call our office and schedule and appointment
at 972-492-6990. You will have a hearing test performed in our
office. A screening test from a hearing aid dealer may not be
adequate. The results of these tests will show the degree of
hearing loss and whether it is conductive or sensorineural and
may give other medical information about your ears and your
Where do I go to get hearing aids?
Because federal regulation prohibits any hearing
aid sale unless the buyer has first received a medical evaluation
from a physician, you will need to see your physician before
you purchase a hearing aid(s). However, the regulation says
that if you are more than 18 years old and are aware of the
recommendation to receive a medical exam, you may sign a waiver
to forego the exam. An otolaryngologist, audiologist, or an
independent dispenser can dispense aids. Hearing aids should
be custom fitted to your ear and hearing needs. Hearing aids
purchased by mail-order typically cannot be custom fitted.
Conductive Hearing Loss
A hearing loss is conductive when there is a problem with the
ear canal, the eardrum and/or the three bones connected to the
eardrum. Common reasons for this type of hearing loss are a
plug of excess wax in the ear canal or fluid behind the eardrum.
Medical treatment or surgery may be available for these and
more complex forms of conductive hearing loss.
Sensorineural Hearing Loss
A hearing loss is sensorineural when it results from damage
to the inner ear (cochlea) or auditory nerve, often as a result
of the aging process and/or noise exposure. Sounds may be unclear
and/or too soft. Sensitivity to loud sounds may occur. Medical
or surgical intervention cannot correct most sensorineural hearing
losses. However, hearing aids may help you reclaim some sounds
that you are missing as a result of nerve deafness.
How expensive are hearing aids?
Hearing aids vary in price according to style,
electronic features, and local market conditions. Price can
range from many hundreds of dollars to more than $2,500 for
a programmable, digitalized hearing aid. Purchase price should
not be the only consideration in buying a hearing aid. Product
reliability can save repair costs and the frustration of a malfunctioning
What kinds of hearing aids are available?
There are several styles of hearing aids:
Behind-the-ear (BTE) hearing aids are placed over the ear and
connected with tubing to custom-fitted earpieces.
hearing aids fill the entire bowl of the ear and part of the
of ITEs are called half-shell and in-the-canal (ITC).
The least visible
aids are completely-in-the-canal (CIC).
Hearing aid options, which are appropriate for your particular
hearing loss and listening needs, the size, and shape of your
ear and ear canal, and the dexterity of your hands will all
be considered in deciding what type of hearing aid is the best
for you. Many hearing aids have special telecoil "T"
switches to aid in use of the telephone and certain public sound
systems. Discuss your need for a T-coil switch while you are
considering hearing aid options.
Will I need a hearing aid for each ear?
Usually, if you have hearing loss in both ears,
using two hearing aids is best. Listening in a noisy environment
is difficult with amplification in one ear only, and it is more
difficult to distinguish where sounds are coming from. If, however,
the quality of hearing in one ear is very different from the
other, one hearing aid may be better than two.
What other questions should I ask?
Ask about charges for the hearing evaluation, dispensing fee(s),
and future servicing and repair.
the trial period policy and what fees are refundable if you
return the hearing aid(s) during the trial period.
Ask about the
warranty coverage for your hearing aids and the consumers' protection
program for hearing aid purchasers in your state.
What will happen at my hearing aid fitting?
The hearing aids will be fitted for your ears.
wearing your hearing aids, you will be tested for word understanding
in quiet and in noise and for improvement in hearing tones.
Next, you will
receive instruction about the care of your hearing aids, the
batteries used to power them, a suggested wearing schedule,
general expectations, and helpful communication strategies.
You will also
practice properly inserting and removing the hearing aids and
How should I begin wearing the aids?
Start using your hearing aids in quiet surroundings, gradually
building up to noisier environments.
Note where and
when that you find the hearing aids beneficial.
Be patient and
allow yourself to get used to the aids and the "new"
sounds they allow you to hear.
Keep a diary
to help you remember your experiences.
Report any concerns
on a follow-up appointment.
The American Academy of Otolaryngology-Head and
Neck Surgery provides these links as a guide to other Internet
resources related to hearing health. The AAO-HNS is not responsible
for the content of other Web sites.
The term otosclerosis is derived from the Greek
words for "hard" (scler-o) and "ear" (oto).
It describes a condition of abnormal growth in the tiny bones
of the middle ear, which leads to a fixation of the stapes bone.
The stapes bone must move freely for the ear to work properly
and hear well.
Hearing is a complex process. In a normal ear,
sound vibrations are funneled by the outer ear into the ear
canal where they hit the ear drum. These vibrations cause movement
of the ear drum that transfers to the three small bones of the
middle ear, the malleus (hammer), incus (anvil), and stapes
(stirrup). When the stapes bone moves, it sets the inner ear
fluids in motion, which, in turn, start the process to stimulate
the auditory (hearing) nerve. The hearing nerve then carries
sound energy to the brain, resulting in hearing of sound. When
any part of this process is compromised, hearing is impaired.
Who gets otosclerosis and why?
It is estimated that ten percent of the adult
Caucasian population is affected by otosclerosis. The condition
is less common in people of Japanese and South American decent
and is rare in African Americans. Overall, Caucasian, middle-aged
women are most at risk.
The hallmark symptom of otosclerosis, slowly
progressing hearing loss, can begin anytime between the ages
of 15 and 45, but it usually starts in the early 20’s. The disease
can develop in both women and men, but is particularly troublesome
for pregnant women who, for unknown reasons, often experience
a rapid decrease in hearing ability.
Approximately 60 percent of otosclerosis cases
are genetic in origin. 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.
What are the symptoms?
Gradual hearing loss is the most frequent symptom
of otosclerosis. Often, individuals with otosclerosis will first
notice that they cannot hear low-pitched sounds or whispers.
Other symptoms of the disorder can include dizziness, balance
problems, or a sensation of ringing, roaring, buzzing, or hissing
in the ears or head known as tinnitus.
How is it diagnosed?
Because many of the symptoms typical of otosclerosis
can also be caused by other medical conditions, it is important
to be examined by an otolaryngologist (ear, nose and throat
doctor) to eliminate other possible causes of the symptoms.
After an ear exam, the otolaryngologist may order a hearing
test. Based on the results of this test and the exam findings,
the otolaryngologist will suggest treatment options.
How is it treated?
If the hearing loss is mild, the otolaryngologist
may suggest continued observation and a hearing aid to amplify
the sound reaching the ear drum. Sodium fluoride has been found
to slow the progression of the disease and may also be prescribed.
In most cases of otosclerosis, a surgical procedure called stapedectomy
is the most effective method of restoring or improving hearing.
What is a stapedectomy?
A stapedectomy is an outpatient surgical procedure
done under local or general anesthesia through the ear canal
with an operating microscope. (No outer incisions are made.)
It involves removing the immobilized stapes bone and replacing
it with a prosthetic device. The prosthetic device allows the
bones of the middle ear to resume movement, which stimulates
fluid in the inner ear and improves or restores hearing.
Modern-day stapedectomies have been performed
since 1956 with a success rate of 90 percent. In rare cases
(about one percent of surgeries), the procedure may worsen hearing.
Otosclerosis affects both ears in eight out
of ten patients. For these patients, ears are operated on one
at a time; the worst hearing ear first.
What should I expect after a stapedectomy?
Most patients return home the evening after
surgery and are told to lie quietly on the un-operated ear.
Oral antibiotics may be prescribed by the otolaryngologist.
Some patients experience dizziness the first few days after
surgery. Taste sensation may also be altered for several weeks
or months following surgery, but usually returns to normal.
Following surgery, patients may be asked to
refrain from nose blowing, swimming, or other activities that
may get water in the operated ear. Normal activities (including
air travel) are usually resumed two weeks after surgery.
Notify your otolaryngologist immediately
if any of the following occurs:
Sudden hearing loss
Any new symptom
related to the operated ear
Since packing is placed in the ear at the time of surgery, hearing
improvement will not be noticed until it is removed about a
week after surgery. The ear drum will heal quickly, generally
reaching the maximum level of improvement within two weeks.
One of the most common birth defects is hearing
loss or deafness (congenital), which can affect as many as three
of every 1,000 babies born. Inherited genetic defects play an
important role in congenital hearing loss, contributing to about
60 percent of deafness occurring in infants. Although exact
data is not available, it is likely that genetics plays an important
role in hearing loss in the elderly. Inherited genetic defects
are just one factor that can lead to hearing loss and deafness,
both of which may occur at any stage of a person’s lifespan.
Other factors may include: medical problems, environmental exposure,
trauma, and medications.
The most common and useful distinction in hearing
impairment is syndromic versus non-syndromic.
Non-syndromic hearing impairment accounts for the vast majority
of inherited hearing loss, approximately 70 percent. Autosomal-
recessive inheritance is responsible for about 80 percent of
cases of non-syndromic hearing impairment, while autosomal-dominant
genes cause 20 percent, less than two percent of cases are caused
by X-linked and mitochondrial genetic malfunctions.
Syndromic(sin-DRO-mik) means that the hearing impairment is
associated with other clinical abnormalities. Among hereditary
hearing impairments, 15 to 30 percent are syndromic. Over 400
syndromes are known to include hearing impairment and can be
classified as: syndromes due to cyotgenetic or chromosomal anomalies,
syndromes transmitted in classical monogenic or Mendelian inheritance,
or syndromes due to multi-factorial influences, and finally,
syndromes due to a combination of genetic and environmental
Variable expression of different aspects of syndromes is common.
Some aspects may be expressed in a range from mild to severe
or different combinations of associated symptoms may be expressed
in different individuals carrying the same mutation within a
single pedigree. An example of variable expressivity is seen
in families transmitting autosomal dominant Waardenburg syndrome.
Within the same family, some affected members may have dystopia
canthorum (an unusually wide nasal bridge due to sideways displacement
of the inner angles of the eyes), white forelock, heterochromia
irides (two different-colored irises or two colors in the same
iris), and hearing loss, while others with the same mutation
may only have dystopia canthorum.
How do genes work?
Genes are a road map for the synthesis of proteins,
which are the building blocks for everything in the body: hair,
eyes, ears, heart, lung, etc. Every child inherits half of its
genes from one parent and half from the other parent. If the
inherited genes are defective, a health disorder such as hearing
loss or deafness can result. Hearing disorders are inherited
in one of four ways:
Autosomal Dominant Inheritance: For autosomal dominant disorders,
the transmission of a rare allele of a gene by a single heterozygous
parent is sufficient to generate an affected child. A heterozygous
parent has two types of the same gene (in this case, one mutated
and the other normal) and can produce two types of gametes (reproductive
cells). One gamete will carry the mutant form of the gene of
interest, and the other the normal form. Each of these gametes
then has an equal chance of being used to form the offspring.
Thus the chance that the offspring of a parent with an autosomal
dominant gene will develop the disorder is 50 percent. Autosomal
dominant traits usually affect males and females equally.
Inheritance: An autosomal recessive trait is characterized by
having parents who are heterozygous carriers for mutant forms
of the gene in question but are not affected by the disorder.
The problem gene that would cause the disorder is suppressed
by the normal gene. These heterozygous parents (A/a) can each
generate two types of gametes, one carrying the mutant copy
of the gene (a) and the other having a normal copy of the gene
(A). There are four possible combinations from each of the parents,
A/a, A/A, a/A, and a/a. Only the offspring that inherits both
mutant copies (a/a) will exhibit the trait. Overall, offspring
of these two parents will face a 25 percent chance of inheriting
X-linked Inheritance: A male offspring has an X chromosome and
a Y chromosome, while a female has two copies of the X chromosome
only. Each female inherits an X chromosome from her mother and
her father. On the other hand, each male inherits an X chromosome
from his mother and a Y chromosome from his father. In general,
only one of the two X chromosomes carried by a female is active
in any one cell while the other is rendered inactive. This is
why when a female inherits a defective gene on one X chromosome,
the normal gene on the other X chromosome can usually compensate.
As males only have one copy of the X chromosome, any defective
gene is more likely to manifest into a disorder.
Mitochondrial Inheritance: Mitochondrias, small powerhouses
within each cell, also contain their own DNA. Interestingly,
the sperm does not have any mitochondria, and consequently,
only the mitochondria in the egg from the mother can be passed
from one generation to the next. This leads to an interesting
inheritance pattern where only affected mothers (and not affected
fathers as their sperms do not have mitochondria) can pass on
a disease from one generation to the next. Sensitivity to aminoglycoside
antibiotics can be inherited through a defect in mitochondrial
DNA and is the most common cause of deafness in China!
In the last decade, advances in molecular biology and genetics
have contributed substantially to the understanding of development,
function, and pathology of the inner ear. Researchers have identified
several of the various genes responsible for hereditary deafness
or hearing loss, most notably the GJB2 gene mutation. As one
of the most common genetic causes of hearing loss, 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. Screening tests for the GJB2 gene are available for
at risk individuals to help them determine their risk of having
a child with hearing problems.
Air Quality Index Ozone is a
gas that is formed in the atmosphere when three atoms
of oxygen combine. Naturally occurring ozone is found
high in the stratosphere surrounding the earth and
in ground-level ambient air. read
Daily Pollen Count Here you will
find the daily pollen count and other helpful allergy
information for the Dallas Fort Worth Texas metroplex