Tag Archives: Connexin

The Genetic Tests Are In!

Close View of a DNA Strand

It’s hard to believe, but it’s been over 3 months since we first learned of Fiona’s deafness. We’ve come so far.

When this journey first began, we had 2 big fears: would Fiona be eligible for the Cochlear Implant and would this prevent us from having a second child?

A month later, our first fear was laid to rest: Fiona was pronounced eligible for the Cochlear Implant. I blogged about this on July 16th.

Yesterday we received the answer to our second fear: Fiona’s deafness does not appear to be genetic.

This is great news as it lays to rest our concerns about having a second child. It’s also good news for adult Fiona as she likely will not pass on hearing loss to her children (if she so chooses to have any).

We couldn’t be happier!



How Did They Test?

About two months ago, Fiona’s doctor drew blood to conduct the genetic testing. Apparently there are 3 known genetic mutations that are common to infant profound hearing loss.

Before I go further, i’ll put out the disclaimer that this information is very technical and difficult to understand. To make matters worse, the websites I found were very heavy in “Doctor-talk” so was hard for me to follow. I did my best to understand the high level concepts, but it’s very possible I missed some key details.

Connexin 26 and Connexin 30

Connexin 26 and 30 are 2 proteins used by the inner ear to communicate from cell to cell. A defect in the “GJB2” gene (good ‘ol GJB2!) can cause these 2 proteins to disrupt communication across the cells in the ear, leading to the inability of the ear system to function properly. Here is one of the better articles I found on the topic from the California Ear Institute.

For two hearing parents to have a deaf child with the Connexin mutation, both parents must have the Connexin mutation. This means the mutation is passed recessively to the child (since neither of the original parents were deaf). Fiona’s testing did not indicate this mutation, clearing her and her children of this possible cause.

Mitochondrial DNA Defect

Mitochondrial DNA defects are the other common genetic cause of hearing loss. Mitochondria are cellular structures that help “power” the activity of cells in your body. A specific genetic defect in the Mitochondria can lead to premature death of some of the cells specifically used for the process of hearing. For a medical layman this is somewhat hard to follow, but here’s a good article I found here: Yale Study.

And here’s a good but technical 4 minute video on the topic:

The mitochondrial DNA defect is only passed on maternally, meaning it can only come from the mother. Fiona did not have this defect either.

So What’s Next?

It should be stressed that medical research is still evolving quite a bit in this area, so its very possible there are other genetic factors at work here of which we’re simply not aware. We can’t know for sure, but as of today all known genetic factors appear to be clear.

At this point it’s unlikely we’ll ever know the root cause of her hearing loss, but we’ve been told that’s the case more then 50% of the cases. Perhaps medicine will shed some new light on this in the years to come, but at least for now we know the odds are low in a recurrence in future children.

Drinks all around!