Q: What are some medical conditions that are linked to the chance of hearing loss in infants and young children?
A: Approximately 3 in 1,000 babies are born with some degree of hearing loss. The cause of hearing loss can be broken down into the following categories:
- Genetic cause - 33% of children with hearing loss
- Non-genetic cause - 33% of children with hearing loss
- Unknown cause - 33% of children with hearing loss (probably half of these are genetic and half are non-genetic)
There is more than one way that genes can cause hearing loss. In fact, there may be as many as 400 different genetic causes of hearing loss.
Q: Can an infant have both syndromic and non-syndromic hearing loss?
A: No, infants with hearing loss have either a non-syndromic form or a syndromic form.
Genetic causes of hearing loss can be 'syndromic' or 'nonsyndromic'. Syndromic means that a person has other related symptoms besides hearing loss. For example, some people with hearing loss are also blind. Usher's Syndrome is one example. There are many different syndromes that have hearing loss as one of the symptoms. 'Nonsyndromic' means that the person does not have any other symptoms related to the hearing loss. Whatever caused the hearing loss does not cause any other symptoms. The more common type of genetic hearing loss is 'nonsyndromic' which includes 2/3 of all genetic hearing losses. A very common 'nonsyndromic' hearing loss is caused by one gene known as Connexin 26 (abbreviated CX26). CX26 alone is the cause in about 1/3 of all children with a non-syndromic genetic hearing loss.
Non-genetic hearing loss is most often caused by illness or trauma before birth or during the birth process. Older infants and young children can also develop non-genetic hearing loss due to illness or trauma.
Some viral infections are known to be associated with hearing loss. These infections carry a chance of causing infant hearing loss if the mother has the illness during pregnancy or passes the infection to her baby during the birth process. Cytomegalovirus (CMV) is the most common of these viral infections.
Low birth weight (less than 1500 grams or approximately 3.3 lbs) is also associated with hearing loss. Prolonged mechanical ventilation (breathing with the help of a machine and breathing tube for long periods of time) increases the chance of hearing loss in infants.
Jaundice at birth, severe enough to require a blood transfusion, is also associated with hearing loss. High levels of bilirubin can damage the nerves that control hearing. Severe distress at birth also increases the chance for hearing loss.
One illness that carries a high chance of causing hearing loss is meningitis. Because meningitis is an infection of the lining of the brain and spinal cord, the sense organs of hearing are especially sensitive to this infection and can be damaged. Also, medications that can be damaging to hearing are sometimes given to infants or children to treat very serious infections. These medications are usually not given for minor illnesses such as ear infections or even pneumonia.
Unknown causes may be genetic or non-genetic. Because of technology and medical breakthroughs, this category will probably get smaller and smaller as more causes of hearing loss are understood.
Q: What is the prevalence (commonness) of hearing loss in children?
A: Hearing loss occurs in approximately 12,000 children each year (3 of every 1,000). According to the National Institute on Deafness and Other Communication Disorders (NIDCD), about 28 million people in the U.S. have some degree of reduced hearing sensitivity.
Q: What is an Auditory Brain stem Response (ABR) test?
A: Auditory (hearing) Brain stem Response - is a test that checks the brain's response to sound and is measured by placing electrodes (non-invasive) on the head to record the brain?s response to sound. For more information, visit
Q: What is an Otoacoustic Emissions (OAE)?
A: Otoacoustic Emissions ? is a test that checks the inner ear response to sound and is measured by placing a very sensitive microphone in the ear canal to measure the ear's response to sound. For more information, visit: http://www.asha.org/public/hearing/testing.
Q: What is the difference between Auditory Brainstem Response testing and Behavioral Audiometry Evaluation?
A. To understand the difference between Auditory Brainstem Response (ABR) testing and Behavioral Audiometry Evaluation (see below for an explanation), it is important to understand how the ear works.
The ear has three main parts: the outer ear, the middle ear, and the inner ear.The outer ear includes the visible portion of the ear and the ear canal. Sound waves travel through these two areas of the outer ear. The middle ear includes the eardrum (the tympanic membrane) and three small bones (ossicles). The movement of the tympanic membrane makes the ossicles vibrate. The inner ear includes a snail-shaped fluid-filled cochlea, which contains thousands of sound receptors (hair cells). The inner ear is responsible for changing the sound vibrations into electrical signals. The electrical signals are picked up by the hearing (acoustic) nerve. The acoustic nerve sends the sound to the brain.
When an adult or child has a hearing loss, one or more of these parts are not working in the usual way. In order to fully test hearing, all parts of the ear, the acoustic nerve, and the brain pathways that are involved in hearing must be tested for proper functioning.
Auditory Brain stem Response (ABR) testing focuses only on the function of the inner ear, the acoustic nerve, and the brain pathways that are associated with hearing. This test is used for babies, children, and adults. For this test, electrodes are placed on the individual?s head (similar to electrodes placed around the heart when an electrocardiogram is done), and brain wave activity in response to sound is recorded. Because this test does not rely on behavior, the adult or child being tested can be sound asleep during the test.It is necessary for infants and young children to be asleep during this test because movement will cause artifact that will interfere with the results and make them unreliable.
Behavioral Audiometry Evaluation tests the function of all parts of the ear, including the acoustic nerve and the brain pathways involved in hearing. Infants and toddlers can participate in behavioral testing once they are old enough to be conditioned to respond to the test sounds in a reliable way,At about 6 months of age, infants can be trained to consistently turn to the source of a sound and are rewarded for the correct response by getting to watch an animated toy (this is called Visual Reinforcement Audiometry or VRA). Older children (2.5 or 3) are given a more play-like activity (this is called Conditioned Play Audiometry). The child being tested must be awake and cooperative during this test.