Tuesday, December 19

Connexin 26

I received a call today from Dr. Choo (see previous post) with the results of Drew's genetic testing. While the results are surprising, I now have an answer to the "Why did this happen?" question.

Drew's genetic test came back with abnormalities in his connexin 26 gene. This is the most common gene for hearing loss. This means that both his father and I carry the recesive gene, and when Drew was conceived, he received two connexin 26 genes with hearing loss, causing him to be deaf. We learned that because we both carry this gene, we have a 25% chance of having a baby with profound hearing loss.

As a result, we now know that this runs somewhere in each of our families. If you would like to know if you carry the gene, please contact your local physician or click here for information on a genetic test for hearing loss. Dr. Choo said that Cincinnati Children's would run the test for anyone in our families wishing to know. Additionally, Dr. Choo said that he will send me some paperwork with the specific test to be run, so if you would like that information, please email me. Please know that you will only have a 25% chance of passing hearing loss on to your child if both you and your partner carry this gene.

In addition, Drew's mitochondrial tested abnormal. Here is some information on mitochondrial hearing loss:
Mitochondrial: Mitochondria are small organelles in our cells that have their own DNA, known as mtDNA. The number of mtDNA base pairs is only about 16,000, but there are many copies of mtDNA in each cell. We inherit all of our mtDNA from our mothers, so if the hearing loss is caused by a mutation in mtDNA, all the children of affected mothers (but none of the children of affected fathers) would be expected to have hearing loss. An mtDNA mutation, in which a G instead of an A is found at position 1555 (called A1555G), causes severe to profound sensorineural hearing loss. However, in some individuals with the A1555G mutation, the hearing loss does not occur until after exposure to aminoglycoside antibiotics. Thus, knowing this mutation is in the family can help to prevent aminoglycoside-induced deafness.

This information has me very concerned because it would mean that his older sister has the mutation, and could become hearing impaired by the use of certain IV antibiotics. We will be having her screened for this in the near future. In addition, it means that my sister could also be a carrier and pass hearing loss on to her children. I am doing a lot of research to learn more about the genetic causes of hearing loss, and will pass information on as I learn it.

For more information on the research being done at Cincinnati Children's hospital on genetic causes of hearing loss, please click here.

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