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Cochlear Implant Program

If your child has not been tested

Background

Approximately 1/500 children are born with hearing loss, and half of these are due to genetic changes.  Genetic hearing loss can be non-syndromic (individuals only have hearing loss) or syndromic (individuals have hearing loss plus other affected parts of the body).  Up to 60% of non-syndromic hearing loss is due to changes in one gene, called Connexin, that we can test for using a small sample of blood.

What is Connexin 26?

Connexin 26 is normally found in the cochlea or inner ear and helps to remove potassium from the fluid inside the cochlea.  This fluid normally helps to regulate the environment in the cochlea so that the hair cells and nerves of hearing can send signals to the brain.  When someone inherits a genetic change in Connexin 26, potassium can not be removed from the fluid in the cochlea.  This buildup of potassium in the cochlear fluid prevents the hair cells from sending signals, resulting in hearing loss. 

How are these genes inherited?

Every child inherits half of their genes from their mother and half from their father.  For recessive disorders such as hearing loss due to a connexin 26 mutation, usually both parents have normal hearing but carry one gene with the connexin mutation.  Approximately 3% of the population are carriers of this genetic change.     

In the diagram below, the big “A” is the “normal” hearing gene and the little “a” is the hearing gene with the mutation in connexin.  For each child there are 4 possible combinations of genes that can be inherited.  These are as follows: 

 

MOTHER(Aa)

A

a

 Father

  (Aa)

A

AA

Aa

a

Aa

aa

AA = ¼ or 25% = child has normal hearing and can not pass down hearing loss genes to their children

Aa = 2/4 or 50% = child has normal hearing but carries the hearing loss gene, and can pass it to their children

aa = ¼ or 25% = child has hearing loss, and his/her children will either carry the gene or have hearing loss

*Every new brother and sister will have the same chances of inheriting these combinations of genes.

What is the reason for doing this testing?

1. To help explain why your child has hearing loss, since most parents do not have trouble hearing.

2. To determine whether or not other brothers and sisters carry the connexin change.  Knowing this will allow us to predict if their children could have hearing loss.  If we know they could be at risk, then they can have their hearing tested as early as possible.  If needed, they will then be able to receive a cochlear implant early on to obtain the best possible development of language and social skills.

3. We will also be looking at how well people do with their cochlear implants and try to relate this to the genetric changes they have.  In the future, we hope to be able to take a small sample of blood from a potential candidate and predict how well they will do with a cochlear implant to give parents realistic expectations about what to expect from the device.

4. Researchers are trying to reverse genetic hearing loss by injecting new genes into the middle ear.  Understanding the basic genetics of hearing loss is an important step in helping to modify this exciting new research.

Who should be tested?

Children with hearing loss, their siblings, and parents can all be tested.  We can also test any relatives of children with hearing loss.  Everyone must register with the hospital, which only takes a few minutes.  To register, call Patt Fuller in the Cochlear Implant Program and make a time to meet with her to fill out the forms.  This will only take a few minutes.  She will ask for your Date of Birth and Health Card.  You may also meet with Dr. Evan Propst who will be available to answer any questions that you may have regarding the process, and to sign a consent form with you. 

What does testing involve?

A small sample of blood is taken by trained blood technicians at The Hospital for Sick Children.  The room is located on the main floor, and is the first door to the right of SHOPPER’S DRUG MART (#8 on the map below).  The whole event will take only a few minutes, and is generally well tolerated. 

What if I don’t have my whole family with me today?...can we be tested another day?

The blood lab is open from Monday to Friday from 7:30am to 4:30pm.  If you do not have your entire family with you today, we recommend testing yourselves today, and returning for a quick visit with the rest of the family another time.  We can pre-stamp your paperwork at this visit to make the next one very fast!

How do I get the results?

The Cochlear Implant Program will either telephone you to discuss the results or will mail the results to you.  You may also meet with Dr. Evan Propst or Dr. Blake Papsin to discuss the results by making an appointment through Patt Fuller in the Cochlear Implant Program.  If you would like further information after this, you can also meet with a genetic counselor to discuss your results. 

Do you test for any other genes?

Yes.  If the test does not detect a mutation in the connexin gene, we will then test the same sample for several other less common genes.  Each time the blood sample is tested, the results will be mailed to you.  You will only have to give a sample of blood once at the beginning, and all testing can be done from that sample.  We will keep that sample in the genetics lab in case any other hearing loss genes are discovered in the future.  WE ONLY TEST FOR HEARING LOSS GENES.

If my child has a syndrome, can we still be tested?

Most syndromes are caused by genetic changes, and we are also able to test for most of these genes.  Therefore, you and your family are more than welcome to participate in this exciting new research!

My child lost his/her hearing after receiving antibiotics called aminoglycosides like Gentamycin OR from meningitis ... can we still have our blood tested?

Many people who lose their hearing due to these medications already inherited a genetic predisposition to becoming deaf from their mother’s side of the family.  We can test for this genetic change, and welcome you to participate in this study.  This also applies to children who lost their hearing due to meningitis, for they may have received these antibiotics as part of their treatment.

Thank you in advance for helping us advance our knowledge of the genetic causes of hearing loss!