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Thread: Second DNA test to rule out CF

  1. #1
    Junior Member
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    Feb 2018
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    Second DNA test to rule out CF

    Hello,

    My name is Laura, I am from the Netherlands. Since we don't have a active CF forum I was hoping to get some answers here.

    My daughter (12 years old) was recently diagnosed with severe nasal polyps. There is no known CF in our family. My oldest daughter has had some chestinfections when she was young, and mij youngest daughter (2 years old) has had 2 pneumonia's in 4 months time.
    CF had to be ruled oud, so they did DNA testing. Yesterday we got the results back, but it didn't make any sense to us.
    They said that there were no signs of CF in her DNA, but they had to do the test again to be 100% sure? Also, our ENT couldn't see the test results due to bad scanning in the computer system, she could only see the message that was sent with the test, and that we had to do the test again.

    I've been researching a lot, but I have never seen anything about doing the test again to rule out for the second time. I asked the ENT why the test needed to be done again, but she didn't know and thought it was strange. She adviced us to wait for the test results, but that's going to take another 3 to 5 weeks.

    Is it normal to do the test again if the first one was negative?

  2. #2
    Senior Member
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    Sep 2016
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    Yes, sometimes the results can show up as negative, but could be a boarder line number so they want to double check. There are some patients who also don't have the typical CF mutations in their DNA, but are treated as such. The second test usually looks at a larger range of DNA besides the typical CF mutations.

  3. #3
    Super Moderator
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    20,879
    When DS was an infant, he had an inconclusive genetic blood test due to an incomplete blood sample. Fortunately, the local hospital had also drawn blood for the test prior to transferring him to a children's hospital, so they had results from that and didn't have to retest.

    It's my understanding in the states there is newborn screening in most areas, which tests for certain genetic markers. If positive, they will conduct a sweat test, if that's high they'll go on to genetic test, which a lot of times only tests for the most common CF mutations. There are over 1500 CF mutations, I believe my child was tested for 100.
    Some states also have genetic testing of the mother during pregnancy, but don't test for ever single mutation, just the most common.

    Meanwhile... Do your children taste really salty when you kiss their foreheads, how is their digestion/weight -- are they underweight, do they have frequent stomach/bowel upsets--- when they've gotten infections have they ever run cultures to see what type of bugs they are growing and what antibiotics is the infection sensitive to.... Common CF bugs are pseudomonas, MRSA, Steno. Maltophilia.

    In my opinion, it's good that they are retesting to find answers to what ever is wrong with your daughter.
    Parent to a child wcf double delta f508.

    Started Orkambi July 2015
    Began Symdeko August 2018

  4. #4
    Junior Member
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    Feb 2018
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    Thank you both for the answers.

    They didn't mention a wider range of testing, just a repeat of the previous DNA test.
    Since 2011 newborns are tested for CF, but my daughter is from 2005, so not tested untill now.

    She did have a lot of stomach issues, but it's been a lot better the last years since we changed her diet.

    Again, thank you. We are just hoping for the best.

  5. #5
    Junior Member
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    Oct 2016
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    Quote Originally Posted by LauraV View Post
    They didn't mention a wider range of testing, just a repeat of the previous DNA test.
    Very odd, I agree. One possibility: for efficiency's sake, sometimes DNA testing is done in two or more phases - for example, the cheaper test to look for the 25 most common mutations, followed by full genetic sequencing (which is more expensive, takes longer, and requires a specialty lab) if you don't find the answer in the first test. Perhaps they mean they need to do a follow-on genetic test rather than just repeating the first test?

    Or maybe they just messed it up the first time. So frustrating when things are unclear!

    Best wishes to you both.

  6. #6
    Super Moderator
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    Dec 2011
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    For what it's worth, my first genetic testing came back inconclusive. Being a geneticist, I found the answer suspicious so I called the facility and talked with the Senior Scientist in charge of all the testing. Sometimes knowing what can happen in a laboratory makes what might sound incompetent, just part of the job. A piece of equipment had been installed that amplifies the DNA in a sample called thermocycling, had gone too high and cooked a number of samples. The Scientist in charge didn't determine what was sent to the patients.

    This isn't the kind of problem you have with genetic testing. The technology for genetic testing is forever changing and improving. It's not impossible to be getting a less reliable test. Repeating the test would eliminate inconclusive test results ideally. A flat repeat of the test is suspicious but I would go along with it as long as you aren't unduly charged for the test and co-pay. It would be great if the test repeat would allow you to ask why you are having a test, done correctly, would never change. The only real difference would be in the details, unless they botched the test. Be mad, be forgiving but find out why. More details is a legitimate reason for repeating a test. In my experience this doesn't happen often and it's likely that you will find the test didn't go as planned.

    They aren't trying to take advantage, usually you get honest people who are happy to answer any questions,

    LL
    67yr. old man, DX CF 2002 by sweat test. Heterozygous S1235R revealed by genetic testing in 2003 & 2012 accepted secondary mutation. 7T, 7T polymorphism established to be virulent. Classification review in 2017 remains CF diagnosis.

    Complete pancreatic atrophy, Bronchiectasis, MRSA, osteoporosis, small duct disease, charming personality.

  7. #7
    Junior Member
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    Feb 2018
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    Thank you for the answers.
    We have an appointment on march 26th, hope to get more answers by then.
    Thanks to all!

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