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Chance of Cystic Fibrosis
- Vraag
- Good evening and best wishes,
Three years ago, following a routine prenatal screening, we discovered that I am a carrier of the E822* (p.Glu822Ter) mutation and that my husband is a carrier of the N1303K mutation. I am currently 16 weeks pregnant, and after prenatal molecular testing of the trophoblast, we were informed that the fetus carries the father’s mutation in a heterozygous state and not mine.
However, a 6T/TG13 allele was identified in a heterozygous state, which, after repeat targeted testing, was found to be inherited from me. Therefore, I carry one pathogenic mutation and the polymorphism in trans. I do not have cystic fibrosis, nor do I have even mild symptoms suggestive of a mild form of the disease.
Given that this allele has been classified as of unknown clinical significance, could you please inform me about the probability that the fetus may develop typical cystic fibrosis?
Thank you very much. - Antwoord
- Dear questioner,
You and your partner are carriers of typical CFTR mutations. You carry the E822* (p.Glu822Ter) variant, and your partner carries the N1303K variant. If an offspring were to inherit both variants (with a 25% probability in each pregnancy), they would develop typical manifestations of cystic fibrosis.
The 6T/TG13 allele detected in both you and the fetus is a polymorphism that modifies the clinical phenotype with low penetrance (i.e., in a small proportion of carriers) and is mainly associated with atypical manifestations of the disease, such as congenital bilateral absence of the vas deferens (CBAVD) in male individuals or very mild/atypical CFTR-related disorders. It is not considered a mutation that causes typical cystic fibrosis on its own.
The fetus carries only one typical CFTR mutation (N1303K) and one polymorphism. This combination does not lead to the development of symptoms of typical cystic fibrosis. Based on the available data, the probability of developing typical cystic fibrosis for this fetus is practically negligible.
Best regards,
M. Poulou - 17.05.2026
