Why Genetic Testing Can Be Wrong

I took my second child in for genetic testing a couple of days ago. My oldest child has cystic fibrosis, and although my two-month-old had a normal newborn screen and a normal sweat test, her doctors and I still felt we should do the genetic testing for CF for that final, more definitive answer. While I was speaking with the genetic counselor, I learned something that I hadn’t known before.

When it comes to genetic disease, at least with CF, there are numerous gene mutations that can cause the disease. In the case of CF, there are over 1600 possible mutations, with more that have yet to be named, but are discovered quite often. However, when a pregnant mother and her partner are tested during the pregnancy for CF carrier status, they are only tested for the top 90 mutations. So being told that they aren’t a carrier could be an outright lie. This I knew. I also knew that 1 in 25 Americans is a carrier for CF (the numbers change slightly based on race). What I didn’t know, was that once a person is tested for carrier status (of the top 90 mutations) and told that she or he is not a carrier, there is still a 1 in 2401 chance that she or he is actually a carrier of a more rare mutation. So couples who think they are in the clear for having a child with CF, have a baby that tests positive for the genetic disease through newborn screening.

If you have been tested for CF carrier status, make sure you ask which test you had, as there are three options available. The first is the 508 First test from Ambry Genetics, which only looks for one mutation, DeltaF508. This is the most common mutation. 90% of people with CF have at least one copy of DeltaF508, while half of people with CF have one copy. The second test checks for the more common mutations, while the CF Amplified checks for 99% of all mutations. That test is your best bet in learning carrier status, although not every mutation has been classified yet.

Being proactive will help you be better prepared for caring for a child with CF and will therefore help that child do better and stay healthier. And if you suspect your older child has CF, it is best to do genetic testing, even if other tests come back negative. Genetic testing will give you the clearest answer.

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About Nancy

I am a freelance writer focused on parenting children with special needs. My articles have been featured in numerous parenting publications and on www.parentingspecialneeds.org. I am the former editor and publisher of Vermont HomeStyle Magazine. I am a wife and mom to a two daughters, one with cystic fibrosis and one who is a carrier for cystic fibrosis.