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 ("the Organ of Corti") 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 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:
This is the responsible cause of approximately 70% or more of all cases of severe to profound deafness. This is where the genetic information (Code) in the DNA 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.
Up to several percent of the normally hearing adult population may be carriers of a recessive gene for deafness.
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.
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
- > Waardenburg's syndome
- > Congenital cytomegalo virus
- > Usher's syndrome
- > Pendred's syndrome
- > CHARGE Association
- > Neurofibromatosis type II
- > Mitochondrial disorders
- > Stickler'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 cytomegalovirus (CMV), rubella, toxoplasmosis, 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. In New Zealand, so far I have yet to see a case of toxoplasmosis or syphilis related deafness ( although currently syphilis is increasing in the general community)
- > 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, or very early life. This also includes some chemotherapy agents ( such as Cisplatin) used to treat childhood ( and adult) tumours.
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 or on 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 sometimes 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 hearing aid trial is important confirmation of the severity of deafness demonstrated by other audiologic tests.
Auditory Neuropathy (Auditory Dys synchrony Spectrum Disorder or ANSD or auditory synaptopathy):
This is a group of conditions which results in poor synchronisation or transmission of auditory nerve impulses from the inner ear along the audtiory nerve. Oto-acoustic emissions may still be present, but the ABR test is severely abnormal or unreadable. An MRI scan is always necessary to asssess auditory dys synchrony spectrum disorder, because sometimes the auditory nerves may not be present, or may be extremely small.
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. Sometimes hearing aids may not be as effective as expected when used to help treat this condition, but most often cochlear implants can help restore clarity to speech.
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 performed at birth (the "Guthrie test")-this includes thyroid function testing.The Guthrie Card test is used mainly to detect inborn errors of metabolism, which are very rare. It can also be used retrospectively to look for CMV ( Cytomegalovirus).
Firstly, this is not always an essential test. It can however be useful to provide an explantation to the parents ( and some degree of "closure") as to why deafness has occcurred. It can be useful to help predict the likely progression of a hearing loss, and into the near future, it may help indicate which children might be suitable for gene transfer treatment.
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) produces a protein which enables inner ear cells to communicate with each other.Testing for abnormalities of this gene are available in New Zealand and in many other countries. The most frequent abnormalities which occur in this gene vary, country by country and sometimes region by region.
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 remain stable, and those in whom the hearing may eventually deteriorate.
We anticipate many more tests will become available in the next few years. To have the genetic test done, a blood test is performed on your child. The DNA may also be stored and re assessed in the future, without the need for another blood test. My current practice is to offer an approximately 240 gene test at Invitae Laboratory in San Francisco, and sometimes an "Otoscope" panel at University of Iowa. These usually take 4-12 weeks to come back with a result- however very often, these results are inconclusive!
MRI Scan: This gives useful information about the anatomy of the inner ear, the brain and auditory nerves. It can be done without a general anaesthetic if your child is under 3 1/2 months of age (which is called a 'feed N wrap' technique) but if your child is older, until the age of 7 or so, they will require a general anaesthetic for the scan-- simply to keep them still enough for the 40 minutes required to do the scan. No x rays are involved with this type of scan.
CT Scan:Generally I dont recommend a CT scan unless the hearing loss is a mechanical " conductive" loss. An MRI is preferred.
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
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.
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.
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.
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.
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
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.
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.
Hearing House , Auckland www.hearinghouse.co.nz
Northern Cochlear Implant Programme www.NCIP.co.nz
Auditory Verbal UK www.avuk.org
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.www.jtc.org
We Hear You Foundation http://www.wehearyoufoundation.org/apps/links/
National Deaf Children's Society (UK) http://www.ndcs.org.uk
The deaf blindness web resource: www.deafblind.com/deafblind.html