Test For The "Normal' CFTR Gene?



For quite a while I had been wondering why genetic testing for CF did not involve looking for the known “normal” CFTR gene instead of looking for one of the many known mutations. This seems like it should be much simpler. It should also have the benefit of not missing a diagnosis because a patient’s mutation(s) had not been identified yet.

I was going to pose the question here, thinking someone like LittleLab4CF might have the answer. Instead I asked the Cystic Fibrosis Foundation and this was their reply:

Hi ---,

Thank you for your message and for including some information about yourself. We apologize for the delay in our response. We are happy to hear you’ve been properly diagnosed and subsequently receiving the appropriate care.

With regard to genetic testing for CF, even the “normal” CFTR gene is not one sequence. There are often multiple mutations within that gene that do not cause disruption in function of the CFTR protein. These mutations are sometimes referred to as polymorphisms. This is why we screen based on known mutations collected through the Mutation Analysis Program (MAP). As you reference, it is not perfect since it is only as good as the data provided by participating patients. That said, if a patient exhibits signs of CF but do not possess the more common mutations, there are subsequent tests that can be run where major deletions or insertions are checked, however such a comprehensive approach is not always (readily) covered by insurers.

We hope we’ve answered your question.

I realized there was a good reason for the current method of genetic testing, and the Cystic Fibrosis Foundation’s comments clarified it for me.


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Very interesting... and goes to show why so frequently a diet or lifestyle that works great for one person is often toxic for another... same as how kalydeco works on gating and some other mutations but hurts DeltaF508. There is huge genetic diversity in the human population, therefore it is important for everyone to experiment on themselves and figure out what works for them, especially regarding diet.