Friday, April 24, 2009

FYI #1 - How CF is Passed from Parent to Child

Another Cf girl who is going thru IUI and fertility treatments just like nick and I posted this and I thought it was great and so I wanted to pass it along to everyone - Thanks Kristin!!!!
At the suggestion of a few people who said they'd like to hear more about CF, I've decided to do a series of "FYI Posts.". I'm glad to have this opportunity to spread CF awareness! I will try not to get too technical with these posts, but, as I am an engineer, that might be a challenge ;)So, here is my first one.Cystic Fibrosis is a recessive, genetic disease. The key word here is "recessive." Recessive means that a child must inherit two copies of the CF gene in order to have CF. A child who carries only one copy of the CF gene will not have CF. And, because a child receives one gene from each parent, if one parent is not a carrier of the CF gene, it is impossible for the child to have CF. CF is just like just like blue eyes - remember that lesson in high school science? Well, if you don't, here's a recap: Every parent carries two copies of a gene for eye color. Blue is a recessive gene and brown is a dominant gene. If a child is born with one brown-eye gene and one blue-eye gene, the child will have brown eyes. A child must have two copies of a blue-eye gene in order to have blue eyes.As I mentioned before, a child gets one gene from each parent. For two parents who are carriers of the CF gene, (e.g. my parents), here are the possible outcomes for a child.So, as you can see, when two parents are carriers of the CF gene, there is a 1 in 4 (25%) chance their child will have CF.Now, let's look at the case in which one parent has CF and the other parent is not a carrier. This almost certain is the case for Greg and I. The reason I say "almost certain" is because genetic testing, (which Greg has undergone), does not account for all of the CF genes (I will explain this more in the next FYI). There is still a 0.4% chance that Greg is a carrier. However, for the moment, we will look at that 99.6% chance. Here is a chart for a CFer having a child with a non-carrier.As you can see, it is impossible for a CFer and a non-carrier to have a baby with CF.Now to look at the 0.4% chance that Greg is a carrier. If that were the case, our chart would look like this:If one parent has CF and the other is a carrier, they have a 50% chance of having a child with CF.What all this means is Greg and I have a 0.4% x 50% = 0.2% chance of having a child with CF. In comparison, the average Caucasian couple has a 0.04% chance of having a child with CF, (so I was wrong in my comment response the other day).So yes, Greg and I have a higher chance of having a child with CF compared to an average couple. However, 0.2% is a very small chance. To put it in even more perspective, 0.2% is the same chance a woman my age, (32.5), has of having a child with Downs Syndrome. It is a chance that we, and my doctors, feel very comfortable with. Align Center