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DEAFNESS IN YOUR CHILD
Your son or daughter may be currently undergoing tests for
deafness or perhaps they may have had deafness confirmed. This can
be a very stressful time for you, your child and the whole family.
There are many people available who can help with information and
practical support to maximise your child's potential to develop
language, education potential and communication with friends and
family. It is important to remember that despite the diagnosis of
"severe or profound deafness," in most but not all instances there
is some residual hearing and it is possible to take advantage of
this to maximise the potential for normal development.
WHY IS MY CHILD DEAF?
Deafness is most commonly due to malformation of or damage to
the hearing organ of the inner ear and its tiny hair cells, which
detect sound waves. This may occur during development in the womb,
or at any stage in the first few years of life. Much less common
causes of deafness involve abnormalities of the ear canal, ear drum
or hearing bones.
Despite a thorough investigation, it may be difficult to be sure
of the exact cause of deafness in your child.
The most common known causes of deafness are:
GENETIC DEAFNESS
This is the responsible cause of approximately 60% or more of
all cases of severe to profound deafness. This is where the genetic
information (Code) is altered in some way to produce abnormal
structures or functions in the inner ear. The abnormal code may
come from one or both parents- but may also occur spontaneously in
children. The deafness may be stable, or in some children may
deteriorate with age.
RECESSIVE INHERITED DEAFNESS
The most common form of genetic deafness is called "autosomal
recessive". This accounts for approximately 80% of inherited
deafness. Parents may wonder how their child can have a genetic
form of inheritance if they can both hear. The reason is that each
parent has two genes for hearing. If both parents have a single
copy of a recessive gene for deafness, and one normal gene, they
will be carriers of deafness. If a child inherits one
deafness gene from each parent, i.e. a double dose, he or she will
be deaf. With recessive inheritance the chance of each subsequent
child being deaf is one in four.
Diagram 1: Recessive inherited deafness
DOMINANT INHERITED DEAFNESS
This accounts for 15-20% of genetic deafness. People with a
dominant form of genetic deafness usually have a deaf parent. The
chance that subsequent children will be deaf may be as high as 50%.
Some dominant genes are not as "strong" and may not necessarily
result in deafness or the deafness may skip a generation.
Diagram 2 - Dominantly inherited deafness
SEX LINKED INHERITED DEAFNESS
In this condition, there usually is a clear pattern of deafness
in males of the family, but minimal deafness or no deafness in the
females. The condition is transmitted by females to their male
children, but is not transmitted by males.
MITOCHONDRIAL INHERITED DEAFNESS
Deafness may rarely be transmitted by the mitochondria, which
are tiny "energy organs" inside cells. This is passed to children
from the mother and is thought to contribute only 1% or less to the
population of deaf children. Family members of children with this
type of deafness should never be given aminoglycoside antibiotics
(e.g. gentamicin, tobramycin) as this may provoke deafness.
SYNDROMIC DEAFNESS
Deafness may occur by itself or it may occur as part of a
syndrome in which the deafness is associated with distinctive
facial features, heart, eye, skin or other organ involvement or
other medical conditions. Syndromic deafness may be inherited from
the parents in a manner similar to recessive or dominant non-
syndromic deafness, or may occur spontaneously or secondary to
infection.
Some of the most common " syndromes" that are associated with
hearing loss are
- Hemi facial microsomia/Goldenhaar Syndrome
- Stickler's syndrome
- Congenital cytomegalo virus
- Usher's syndrome
- Pendred's syndrome
- CHARGE Association
- Neurofibromatosis type II
- Mitochondrial disorders
- Waardenburg's syndrome
OTHER CAUSES OF DEAFNESS
- Prematurity
- Difficult birth
- Very low birth weight
- Jaundice after birth.
- Infections -some of the most common occurring infections that
may spread to baby in the womb include toxoplasmosis, rubella,
cytomegalo virus (CMV), herpes type viruses and syphilis. CMV and
Meningitis are the most common infections to cause deafness in
early childhood. Both may also result in a progressive loss of
hearing over several or many years.
- Chemical damage: the most common form of deafness in this
situation is due to Gentamicin or other potent antibiotics used
usually in an intravenous form because of the infections during
pregnancy.
WHAT CAN BE DONE ABOUT MY CHILD'S
DEAFNESS?
CONFIRMATION OF THE SEVERITY OF THE
DEAFNESS
Deafness is confirmed using a variety of audiologic tests. Your
audiologist will also discuss these with you. If your child is new
born or in the first few months of life, testing is performed by
measuring the electrical impulses in the hearing nerves
(auditory brainstem response testing,
ABR.) Small earphones are placed in your child's ears
and clicks or short sounds are passed into the ears. Electrical
impulses are measured from small electrodes/gelpads placed on the
skin. This is done whilst your child is asleep and may need to be
performed under a general anaesthetic. Older children who are able
to turn their heads to sound or to reliably respond to sound can be
tested in a sound- proof booth using room speakers or
headphones.
Oto-acoustic emissions are tiny
sounds, which are actually produced by hair cells in the inner ear.
These can be measured. Absent emissions may indicate inner ear hair
cell damage. Otoacoustic emission testing is usually performed at
the same time as ABR or sound-proof booth testing.
Although hearing tests are very accurate in predicting the level
of hearing, it is possible that the ABR test could over- estimate
the severity of hearing loss. In very rare instances, possibly
because of prematurity of the auditory nerve, the absence of an ABR
response does not necessarily always imply total deafness. The
progress gained with a
hearingaid
trial is important confirmation of the severity of
deafness demonstrated by other audiologic tests. Generally speaking
a hearing aid trial duration is between 3 - 6 months.
A Comment on Auditory Neuropathy:
This is a group of conditions which results in poor
synchronisation of auditory nerve impulses. Oto-acoustic emissions
may still be present, but the ABR test is severely abnormal.
Deafness of varying severity results. Most often, the ability to
understand speech is worse than expected, given a certain degree of
deafness and the hearing may appear to fluctuate from day to day.
Speech development is significantly impaired.
OTHER INVESTIGATIONS MAY INCLUDE:
BLOOD TESTING This may be necessary to test
blood chemicals (e.g. Thyroid hormones) or to test for abnormal
genes. In New Zealand, all infants have a variety of blood tests
also performed at birth (the "Guthrie test")-this includes thyroid
function testing.
GENETIC TESTING There are more than 400 abnormalities of genes
described which may cause deafness. Only a handful are able to be
tested on a "routine" basis. Some are able to be tested in research
laboratories.
At this stage, we know the most common cause of non-syndromic
recessive inherited deafness is due to an abnormality in the
connexin 26 gene (about 20% of all children in New Zealand and
Australia with non- syndromic recessive deafness have an
abnormality in this gene.) This gene when functioning normally
produces a protein which enables inner ear cells to communicate
with each other.Testing for abnormalities of this gene are
available in New Zealand. in addition, we are able to test for
related abnormalities in several other genes as required.A
"positive" test result may be very helpful to clarify the cause of
deafness, but a negative result does not mean that the deafness is
not genetic-it may simply be that another abnormal gene may be
involved. Defining a genetic anomaly may not only give a person or
family "closure" but in some instances it may help identify those
in whom the hearing would be expected to remaind stable, and those
in whom the hearing may eventually deteriorate.
We anticipate many more tests will become available in the next
few years.
CT SCAN: This gives excellent
anatomic detail of the inner ear, and is particularly useful for
the evaluation of progressive deafness and for suitability for
cochlear implantation. In 80% of cases of congenital deafness, the
inner ear looks normal on CT scanning- as the inner ear hair cells
are too small to be seen by the scanner.
MRI SCAN: This gives useful
information about the anatomy of the inner ear, especially after
meningitis. Good views of the brain and auditory nerve can also be
obtained.
OPTHALMOLOGY DOCTOR (EYE SPECIALIST)
REFERRAL: This is advisable in all newly diagnosed hearing
impaired children to ensure there is no eye abnormality.
Up to 60% of all children with hearing impairment will have
visual difficulties or eye abnormalities.
ERG testing: (Electro
retinography) This is another electrical type test similar to the
ABR. A flash of light is made in front of your child's eyes, and
the brain waves which results from this are measured. This is
useful in particular to exclude Retinitis Pigmentosa which can
occur with Usher's Syndrome. This test is performed at the
recommendation of the eye specialist.
HEARING TESTING FOR OTHER FAMILY
MEMBERS: This may be very useful and important to develop a
better picture about the pattern of inheritance in the family- and
may clarify the likelihood of deafness in further children, and the
likelihood of deafness occurring later in your child's
children.
GENETIC EVALUATION AND COUNSELLING
Genetic counselling
An individual or family may wish to see a geneticist for a
variety of reasons. In the case of hearing loss, common questions
are how genetic factors could cause hearing loss, whether there are
any associated medical complications, whether the hearing loss
might progress, and what the chances are that another family member
might be born with or develop hearing loss.
EVALUATION
The genetic evaluation is usually done by a team made up of a
geneticist, (a physician specially trained to recognize signs of
genetic conditions) and a genetic counsellor. The medical history
(including records from the Audiologist and Otolaryngologist) and
family history are reviewed and a physical examination is
performed. The medical history may identify a medical cause of
hearing loss such as a serious illness, an injury, or an infection
the mother had in pregnancy, or it may point out an important
symptom of a genetic condition, such as kidney infections or
difficulty seeing in the dark. The physical examination may reveal
subtle characteristics that can be related to specific genetic
conditions. These characteristics by themselves may not be
abnormalities, and they may appear to be unrelated to hearing loss.
For example, small pits in front of the ears could indicate
branchio-oto-renal syndrome, which also involves the kidneys; a
white forelock could be part of Waardenburg's syndrome; night
blindness or tunnel vision could indicate Usher syndrome, or severe
near sightedness could be a sign of Stickler syndrome.
COUNSELLING
Even when the cause of the hearing loss remains unknown, the
family can be given estimates of the chance it will recur in
another relative. These estimated risks are based on studies of
many families with similar family histories. For example, if the
family is a hearing couple who has had one child who is profoundly
deaf, the chance that the next child would be deaf is about 10%,
but is variable and could be as high as 25% or extremely low. If
both parents are deaf, and the cause of their deafness is unknown,
the chance that their first child would be deaf would also be about
10%.
Particularly in the case of hearing loss, people may have quite
different attitudes about deafness in their family. For example,
some hearing parents might be concerned about having another child
who is deaf, while others may feel
that the hearing loss would not pose a problem, but would want
to know if any other medical problems might be involved. Similarly,
deaf parents may feel comfortable about their own abilities, but
would prefer not to have a deaf child, whereas other deaf parents
may be more concerned about the challenges of raising a hearing
child.
HEARING AIDS
Once deafness has been confirmed it is recommended that hearing
aids are fitted if the loss occurs in both ears. It can take a
considerable period of time to have the hearing aids adjusted
perfectly. Your child needs strong and persistent encouragement to
use the hearing aids as much as possible. Your child's ability to
benefit from the hearing aids will be monitored by your
audiologist.
COCHLEAR IMPLANTS
A cochlear implant is an electronic device that is used to
transmit sound directly into the inner ear and hearing nerves. It
has an internal part that is buried under the skin of the scalp and
is practically invisible. There is an outer portion rather like a
hearing aid which transmits sound through to the inner device. The
cochlear implant is of benefit for children with profound hearing
loss who do not respond well to the most powerful hearing aids and
is also potentially of great value to adults with profound hearing
loss. The best time to have an implant inserted is within the first
two years of life, or as soon as possible following loss of
hearing. For many profoundly deaf children, a cochlear implant will
enable them to participate in the hearing world, to learn to speak
and to attend their local school.
Cochlear implant assessment is performed by a multidisciplinary
team which includes surgeons, audiologists, habilitationists,
counsellors and speech-language therapists.
MAXIMISING YOUR CHILDS ABILITY TO HEAR--
SOME RESOURCES
Despite the diagnosis of deafness, most commonly there is some
residual hearing. It is often possible to use this hearing to help
with the development of speech and language. Much information
obtained from listening to speech is "excess" to requirements when
hearing is normal. Those with hearing loss can learn language
through more limited information, such as the rate and rhythm of
speech, tonal variations, the duration of words etc. Most often, a
specialised therapist is necessary to help maximise this
potential.
Alternatively, for those who chose sign communication for their
child, early intervention with a specialised therapist is
vital.
Advisers on Deaf Children: These are
wonderful resource people, funded through the Ministry of Education
to assist you with therapy and intervention options. In smaller
centres, they may be also able to help with hearing therapy.
Advisers on Deaf Children are available through Special Education
Service (In the phone book under Specialist Education
Services.)
Other important people intimately involved with the development
of speech and language are Speech-Language
Therapists, Teachers of the
Deaf and Auditory Verbal
Therapists.
Teachers of the Deaf generally are based at Kelston
Deaf Education Centre in Auckland and van
Asch Deaf Education Centre in Christchurch.
Speech-Language Therapists are based at most primary schools but
the availability of speech and language therapy for deaf children
is currently very limited in Auckland. There are some private
speech and language therapists available in the community.
Hearing House, 251 Campbell Road,
Auckland (ph:579-2333) is a free service set up by the New Zealand
Cochlear Implant Trust partly at the instigation of hearing parents
with deaf children. It provides oral habilitation and excellent
support for families and children with moderate to profound
deafness. Children are taught to maximise their residual hearing in
order to understand) language and to speak. A visit to Hearing
House is strongly recommended for all parents of children with
newly diagnosed deafness.
OTHER OPTIONS
New Zealand sign language is a rich and expressive language in
its own right. It is certainly an option to have your child learn
this so that they may communicate with other deaf children and deaf
adults. Choosing your options is a difficult task and is sometimes
best considered with your Adviser on Deaf Children and perhaps by a
visit to Kelston Deaf Education Centre or Van Asch Deaf Education
Centre. Exclusive use of sign language would preclude the option of
cochlear implantation in most cases.
FURTHER RESOURCES: SOME SUGGESTIONS
- http://www.deafnessatbirth.org.uk
An excellent reference site for many aspects of raising a child
with hearing loss
- John Tracy Clinic- this has correspondence courses for
pre-school hearing impaired children and their parents. I strongly
recommend this as a resource. The John Tracy Clinic has private
sponsorship and thus is free. Contact address is John Tracy Clinic
Director, Correspondence Education, 806 West Adams Boulevard, Los
Angeles, California 90007, USA, telephone
00-1-213-748-5481.Internet http://www.jtc.org
- Auditory Verbal International, Inc. (AVI) 2121 Eisenhower
Avenue, Suite 402 Alexandria, VA 22314 Phone 001 703 739 1049 Fax
001 703 739 0395 Internet http://www.auditory-verbal.org
Auditory Verbal International is a private non-profit
international membership organisation with the objective of
promoting listening and speaking as a way of life for deaf or hard
of hearing children.
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