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CF chance

Question
My wife is 22 weeks pregnant and she was checked for 90% of CF mutations and the results were that the polymorphism p.V470M (het) rs213950 was detected. What are the chances for the foetus inheriting CF or some other disease? I have not been tested for CF.
Answer
Dear friend,
Your wife is 22 weeks pregnant and was tested for 90% of CF mutations. No pathological mutations were detected, but only the polymorphism PV470M (polymorphs V470M and M470V are benign without any clinical relevance - Dequerker 2009, Castellani 2008).
With this way of testing for CF the chance of having a child with CF is reduced, if you are a carrier of a CF mutation as well, and this chance is further reduced if you are checked for more CF mutations.
Yours friendly,
Dr. Stavros Doudounakis
06.01.2015
6.1.15
To give some concrete numbers: if the mutation detection rate of the test is 90% and your wife has been tested to be negative for CF causing mutations, the chance that you as a couple will get a child with CF is 1/35.088 (0,0028%) when the other partner is untested. If the other partner is tested as well, and will come out to be a carrier, the risk of having a child with CF is 1/1164 (0,086%) but if the partner will come out to be also negative, the rest risk (as no test has 100% detection rate) is 1/357.143 (0.00028%) [according to Castellani et al. in the Journal of Cystic Fibrosis 2010, 9:165-178: “Benchmarks for Cystic Fibrosis carrier screening: A European consensus document.”] .
D. d'Alquen