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Question on the genetic testing of the sibling/carrier yes or no?
- Question
- Hello,
we have a child with CF, as mutation deltaF508 homozygously has been detected.
A genetic testing of us parents revealed, that my husband, as well as me are carriers of the deltaF508.
Now a genetic testing of our second child had been initiated. CF had been excluded via sweat test.
The genetic testing stated that the familial mutation in the CFTR-gene has not been detected in this child. A broader investigation testing furhter mutations in the CFTR-gene could not be justified in case of the familial constellation.
Now my question: can we assume that our healthy child is either not a carrier of CF or would it be theoretically possible, that this child carries another mutation as a carrier for CF?
I am very glad about an answer and thank you already in advance. - Answer
- Hello,
Cystic Fibrosis (CF) is inherited in an autosomal-recessive order, i.e. in case two partners are heterozygous healthy carriers of a CF-mutation, children of this couple have a risk of 25% to suffer from CF, a risk of 50% to be healthy carriers of one of the both parental CF-mutations and 25% chance to have inherited the healthy CFTR-gene from both parents.
Your second child has obvisouly not inherited the F508del-mutation either from you nor from your husband (corresponding to the statement "the familial mutation has not been detected"), whereby it is in respect of this mutation homozygously healthy and does not have any risk to transmit this familial mutation to its offspring.
It is however indeed like this, that your child could theoretically carry any other mutation in one of its both CFTR-genes, that emerged newly in it (so-called new or spontaneous mutation). This means the child would be in this case a CF-carrier with a 50% risk, to transmit this newly emerged mutation to its offspring. Such events are however extremely seldom, so that you child is with the highest probability not a CF-carrier.
The fact that in any living creature not-predictable spontaneous mutations can occur has as a consequence that the statement "there is no risk" of being ill or being carrier can never be made, but the statement has to be: "there is no increased risk (in comparison to the general population)."
I hope to have answered your questions,
Yours sincerely,
Prof. Sabina Gallati - 15.07.2013
