Tuesday, April 11, 2017

When Answers Aren't Actually Answers

Last fall, before Spud was born, we met with a genetics counselor.  In Ontario, part of the standard testing for children with hearing loss is a genetic work-up.  It's optional, but we decided to pursue it, even though, at the end of the day, the answers wouldn't change a thing.  Depending on the results, the testing might have been able to tell us if Bean's loss was going to progressive, if there were other things that co-occurred with it such as vision loss, and the odds of future children having similar hearing loss.

Quick biology refresher:  Human beings are "programmed" by our genes.  Children get half their genes from their mom, half from their dad.  Boys are XY and girls are XX.   For a boy child (like Bean or Spud), David would have passed on his Y and I would have passed on an X (it's all I can do really).  Different genes are "expressed" in different ways.  Some genes are expressed through eye color, hair color, nose shape, etc.  Other genes are present, but aren't expressed (carrier genes).   We have learnt a lot about the human genome and know what some of the genes do.  There are way more that we don't even come close to understanding yet.

Our meeting last fall entailed talking with a genetics counselor at length, giving as detailed a genetic history as we possibly could, and Bean getting some blood drawn.  Between then and now, Bean's blood was sent off to some lab somewhere at which they tested it extensively looking for gene variations associated with hearing loss.  Today was results day.

We had been warned that genetic testing might not show anything, but in our case it did show something.  Bean has a variation in the GJB2 sequence.   I do not know what those letters stand for, just that they are important.  Variations in the GJB2 gene are linked to hearing loss.  So we have our answer, right?  WRONG!  Even though Bean has the GJB2 gene variation, the type of hearing loss it causes is not the type of hearing loss he has.  GJB2 linked hearing loss is usually high frequency and profound, neither of which fit Bean's loss.  However, the gene can also be expressed in other ways, such as patchy thickening of the skin, which Bean has (as do I).  

So, in short, he has a genetic variation that is linked to hearing loss, but it is not what is causing his hearing loss.  At this point the geneticist believes that Bean's hearing loss is hereditary (he got it from me) on a part of the genome that they have not yet identified.  The geneticist says that I am the prototype for Bean, so that's a interesting position to be in.  We were also told that there is probably a 50/50 chance of future children having the same type of loss and that we need to make sure future children are thoroughly tested for hearing loss as soon as reasonably possible after birth and followed.

Was the testing worth it?  It was interesting for certain. And I find it amusing that we've got ourselves a zebra, because really, what are the odds of having a genetic variation associated with hearing loss that isn't causing the genetic hearing loss?


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