Re: What causes deafness if parents aren't?

Dear Deyuanna, it was really nice to see such a stimulating question from the student of 7th grade. Before trying to explain you anything in detail I wanted to give you an overview of how we hear, and what can be various possible causes of hearing loss or deafness among individuals. I feel this introduction will help you to understand the concept of how our auditory system works.

Hearing occurs when sound waves reach the structures inside your ear, and your ear converts the sound wave vibrations into nerve signals that your brain recognizes as sound. Your ear consists of three major areas: outer ear, middle ear and inner ear. Sound waves pass through the outer ear and cause vibrations at the eardrum. The eardrum and three small bones of the middle ear — the hammer, the anvil and the stirrup — amplify the vibrations as they travel to the inner ear. There, the vibrations pass through fluid in the cochlea, a snail-shaped structure in the inner ear. Attached to nerve cells in the cochlea are thousands of tiny hairs that help translate sound vibrations into electrical signals that are transmitted to your brain. The vibrations of different sounds affect these tiny hairs in different ways, causing the nerve cells to send different signals to your brain. That's how you distinguish one sound from another.

Hearing loss or deafness can be defined as the total or partial inability to hear sound in one or both ears. Minor decreases in hearing are normal after age 20. Some deafness related to nerve damage affects 1 out of 5 people by age 55.

For some people, hearing loss may result from a gradual buildup of earwax, which blocks the ear canal and prevents conduction of sound waves. Earwax blockage is one of the more common causes of hearing loss among people of all ages.

Most hearing loss results from damage to the cochlea. Tiny hairs in the cochlea may break or become bent, and nerve cells may degenerate. When the nerve cells or the hairs are damaged or missing, electrical signals aren't transmitted as efficiently, and hearing loss occurs. Higher pitched tones may become muffled to you. It may become difficult for you to pick out words against background noise.

Ear infection and abnormal bone growths or tumors of the outer or middle ear can cause hearing loss. A ruptured eardrum also may result in loss of hearing.

Thus in a nutshell, deafness can be divided into 2 categories:

    * Conductive loss:  occurs because of some mechanical problem, such as fluid in the ear. The 
three tiny bones of the ear (ossicles) may fail to conduct sound to the cochlea or the eardrum 
may fail to vibrate in response to sound.
    * Nerve loss: occurs when the nerves involved with hearing are injured.

'Till here we can see that there is no correlation between parents or child being deaf simultaneously. So, if parents are deaf its not necessary that their child will be deaf or vice versa.

But the story doesn’t end here, its important to note the in children, hearing problems may cause speech to develop slowly. That’s the reason there is a saying ‘Deaf and Dumb'. This simple saying has important scientific message i.e. if a child cannot hear any sound from the time he is born then in most of the case it will be 'dumb' too. Here come an interesting question that how can a child be born deaf? Does it have to do with something from its deaf parents?

Apart form the above-mentioned causes there can be genetic reason involved in deafness. But they are more indirect reasons and come as a side effect of other severe genetic disorders. Just to give you some examples some of these disorders include

    * Osteogenesis imperfecta
    * Bjorn pili torti and deafness syndrome
    * Trisomy at chromosome13 S
    * Multiple lentigines syndrome 
    * Hereditary nephritis   

Some of these diseases can be inherited from one generation to the other. So, by now hopefully you can guess what I mean to say. If not then here is the explanation: assume mother of a child has ‘hereditary nephritis’ and she is deaf because of the damage in cochlear nerve. If she gives birth to a son then he is also likely to suffer from the same disease, which includes deafness as one of its side effect or symptoms. From here we can show that there is possibility that if parents are deaf then children can also be deaf but its not very common to see this. Most of these genetic disorders are not inherited so commonly from parents to children thus if parents are deaf its not at all necessary that their children will be deaf too.

From my previous explanation we can say that genetic factors are not most common cause for deafness. So, it’s not very likely to see deaf parents with deaf children or vice versa.

Deyauanna, I have tried to be as simple as possible but if you still have any confusion feel free to contact us back. We will be more than happy to help you out from you more mind boggling queries.

Below is the link of the tutorial, which can be more help full and informative for you to understand my answer.

http://www.nlm.nih.gov/medlineplus/tutorials/hearingloss/htm/index.htm

Cheers and have fun

Amit