Probability of outbreak

Question

Dear experts,
I got the information yesterday that in case of my dauhgter (7 months) 33 mutated genes of rh117 have been detected. Test (OLA POR).
She has been named as a healthy carrier of the gene defect. She is told to do a sweat test now. What does that mean?
Can this illness break out? Or only if both parents have inherited this defective gene? Or is only one parent necessary to evoke the illness to the child?
(I do not know at the moment, if we both parents are carrier or only one of us).
I only find information that both parents have to be carrier for the child is going to suffer from the illness and is not only a carrier.
In case the sweat test will be positive, does that mean that she is already suffering from CF or can she only be a healthy carrier in spite of this? How is it really?
I am very afraid and would welcome a quick answer.
Thank you.

Answer

Hello,
without detailed knowledge of the result this question can not be answered securely. In case I assume that the 7 month-old girl has been diagnosed to be heterozygous for the mutation R117H ("healthy carrier"), then up to this timepoint the illness Cystic Fibrosis has not been diagnosed by molecular-genetic methods. The questions is, of course, why a molecular-genetic investigation had been done at all. In case there are any clinical symptoms, a sweat test should be performed in any case in order to be able to exclude CF to the greatest possible extent (or confirm it, however).
People, who have inherited from one parent the genetic variant R117H and from the other parent a "healthy" CFTR-gene, are named as healthy carriers. These healthy carriers do not suffer from CF themselves. However, the test is covering 33 mutations and therefore it is not possible to exclude that a mutation in the CFTR-gene, which is not covered from the test, is inherited from the other parent, the performance of a sweat test had been recommended in this case for being on the safe side.
One should make a comment on the genetic variant R117H: this variant can exist on two genetic backgrounds, one so-called 7-T-allele or a 5-T-allele. The latter would be graded as a CF-mutation, the first only in rare exeptional cases.
I would recommend in any case, to get the result of the molecular-genetic investigation explained in a session of genetic consultation. Sites of genetic consultation are available at all university hospitals. In many places there are also ambulant specialists for human-genetics.
Yours sincerely,
Prof. Dr. M. Stuhrmann-Spangenberg

15.09.2008